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WBBSE Solutions For Class 9 English Functional Grammar Chapter 2 Pronouns

January 17, 2025July 20, 2023 by vasantha

Chapter 2 Pronouns

You know that a Pronoun is a word used for a noun or a clause.

Ram is not here; he is ill.
He failed, which broke his heart.

Read And Learn More WBBSE Class 9 English Functional Grammar

Pronouns may be divided into the following eight classes:

Personal (including Possessive) – – I, thou, ye, you, he, she, it, my, your, yours, hers, ours, etc.
Demonstrative – This, that, such, so, etc.
Relative Who, which, that, what, as, whoever, whatever, whichever, etc.
Interrogative- Who, which, what, etc.
Distributive Each, either, neither, etc.
Reflexive and Emphatic – Myself, thyself, himself, etc.
Indefinite -One, any, some, they, etc.
Reciprocal-Each other, one another.

WBBSE Solutions For Class 9 English Functional Grammar Chapter 2 Pronouns

Chapter 2 Pronouns Personal Pronouns

Personal Pronouns are so called because they stand for persons, viz.
The First Person denotes the person or persons speaking: as, I, my, me, we, our, etc.
The Second Person denotes the person or persons spoken to as, you, thou, your, etc.
The Third Person denotes the person or persons spoken of: as, he, she, it, they, their, etc.

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The form of Personal Pronouns varies according to their use in the sentence as subjects and objects. To indicate ownership or some other relationship, they take possessive forms.

WBBSE Solutions For Class 9 English Functional Grammar Chapter 2 Pronouns personal pronouns

Personal Pronouns I, we, she, and he, are all used as subjects in the Nominative:

He knows – I know the boy.
We shall go- They were present there.

The objective forms me, us, her, him, they are used as direct and indirect objects of verbs or after prepositions

I saw her- I gave him a book.
He talked with me- Ram spoke to her.
We tried for him- Between him and me.

In formal English, when the pronoun comes after the verb to be, the nominative form of the pronoun is the grammatically correct usage

Who’s there? -It is I.
Was it they?- It was they.

In formal conversation, however, the objective form is often used after the verb to be: It’s me.

Who’s there? – It’s me
Was it them?
That’s her.
I wouldn’t have done this if I were him.
Do you think he did it?
I am not sure.
It might have been him.
(In formal English “It might have been he” is preferred).

But the nominative form must be used when the pronoun acts as the subject of a verb and is followed by a clause

It was he (not him) who helped me.
It was I (not me) who arranged the meeting.

When a pronoun is put with some other word in the objective case, the pronoun must also be in the objective case

The boy is known to him and me (not I).
I brought this for you and him (not him).
The book may be given to Ram or me (not I).
You abused both him and me (not I).

The case of the pronoun following than and as has to be determined by mentally supplying the verb.

He is more intelligent than I (am).
He is taller than I (am).
He knows you more than (he knows) me.
He is not so strong as you (are).
He loves you as much as (he loves) me.
I don’t have more money than he (has).

In colloquial style, however, the objective form is often used in place of nominative after the verb to be followed by an adjective:

He is more intelligent than me (= than I am).
He is taller than me (= than I am).
You are cleverer than him (= than he is).
He is richer than us (= than we are).
He is several years older than me (= than I am).

With transitive verbs, the choice of the subject and object forms depends upon the sense of the complete sentence case

I know you better than he (does) (= he knows you).
I know you better than him (= I know him).
You like her as much as I (= as I like her).
You like her as much as me (= as you like me).
He helped you as well as I (= as well as I helped you).
He helped you as well as me (= as well as he helped me).

‘Between’ is a preposition and any pronoun that follows it must be in the objective

Between you and me
Between her and she
Between him and me
Between Ajoy and me
Between you and him

‘But’ when used as a preposition is followed by a pronoun in the objective case:

Nobody was present there but me (not I).
None but him (not, he) passed the test.

‘Let’ is followed by a pronoun in the objective case:

Let us go.
Let him and me do the job.

It will be seen that the Possessive Case of most Personal Pronouns has two forms. Of these:

My, they, her, its, our, your, and there are called Possessive Adjectives, because like adjectives, they are used before nouns: my book, your name, it’s color.

Mine, yours, hers, ours, theirs are called Possessive Pronouns, because they are now used without the noun and instead of the noun to which they refer:

Whose coat is this? It is mine (= my coat).
His is used both independently and before a noun:
This book is his. Or, This is his book.
Mine, thine, hers, ours, yours, theirs are used

When the noun is understood:

“Whose book is this? It is mine”. “This is my pen; where is yours?”
When a verb comes between the noun and pronoun:
This book is mine. This house is theirs.
When the pronoun is preceded by of:
This book of mine is cheap.

Caution: The possessive forms hers, ours, yours, its, theirs, etc. should never be written with the apostrophe. Thus, it is wrong to write her’s, it’s, your’s or yours’, their’s or theirs’, etc.

It should not be confounded with it which means it is or it has.

( hers, ours, yours, its, theirs প্রভৃতি possessive pronoun লিখতে “s”-এর পূর্বে কোনোও apostrophe দেবে না। চিঠিতে কখনও your’s faithfully লিখবে না।)

The Gender and Number of Personal Pronouns:

The pronoun must be of the same gender and number as the noun for which it stands; but when the sex is uncertain, or not clearly stated, we commonly use the neuter pronoun it.

(Pronoun—এর Number ও Gender সেটা যে noun-এর পরিবর্তে বসেছে সেই অনুযায়ী হয়। Noun-টি স্ত্রী বা পুরুষ বোঝা না গেলে আমরা সাধারণতঃ তার পরিবর্তে it ব্যবহার করি। )

The boy (or boys) has (or have) done his (or their) work.
The girl (or girls) has (or have) done her (or their) work.
It is a healthy baby.

But when the neuter form is not allowable, we sometimes use two pronouns, one masculine and the other feminine.

Every member can express his or her views.
Every boy or girl may do as he or she likes.

Chapter 2 Pronouns Exercise

Question 1. Point out the Personal Pronouns and the person and number of each. One is done for you. He told me to follow him.
Answer: me – First person singular number, him – Third person singular number.

I have lost the book you gave me.
I have sent your brother to him.
They are angry with me.
It is a pleasure to talk with him.
We will follow you.
He told them that they should mind their business.
We should do what you tell us to do.
It was these books that I wanted.
This pen is his, where is mine?

Chapter 2 Pronouns Demonstrative Pronouns

The words this, that, these, those, such, so, and one when used alone are Demonstrative Pronouns; when used with nouns, they are Adjectives. So cannot be used as an adjective.

This (or that) is my house.
What I mean is this.
Such (what was suggested) was not my object.

These are called Demonstrative Pronouns as they point out some objects to which they refer.

This (these) refers to something that is near to the speaker in position, time, or thought; That (those) denotes something being more distant: This house is ours, not that.

The uses of this and that as Pronouns:-

When two nouns have been mentioned before, this refers to the latter, and that to the former (পরের জিনিষটি বোঝাতে this এবং আগের জিনিষটি বোঝাতে that ব্যবহৃত হয়।) :

Work and play are both necessary; this (= play) gives us rest, and that (= work) gives energy.

Dogs are more faithful than cats: these (= cats) attach themselves to places, and those (= dogs) to persons.

They are often used for preceding nouns or clauses:

His book is better than that (= book) of Jadu.
I have read Latin, and that (I have read Latin) at Oxford.
He went there, and this (= the fact that he went there) proves his courage.

Chapter 2 Pronouns Reflexive And Emphatic Pronouns

Reflexive and Emphatic Pronouns are formed by adding –self to my, your, him, her, it, and -selves to our, you’re, and them:

Myself -Ourselves
Yourself -Yourselves
Himself -Themselves
Herself
Itself.

Though the same in form they are different in use:

They are Reflexive when the doer is both the subject and the object of the action expressed by the verb ( subject এবং object একইজনকে বোঝায় )

I hurt myself – He looked at himself in the mirror.
He lost himself – Can you see yourselves in the mirror?
They cursed themselves.

(myself, himself, themselves, yourselves object 4 subject object একই লোককে বোঝাচ্ছে। )

They are Emphatic when used with nouns or pronouns for the sake of emphasis (জোর দিবার জন্য ব্যবহৃত হয়)

I myself did the work.
I saw the man himself.
You yourself can do the job.
They themselves confessed their guilt.
The town itself is very large.

(এখানে myself, himself, yourself, themselves, itself ইত্যাদি word গুলি জোর দেবার জন্য ব্যবহৃত হয়েছে।)

“I myself saw the man” and “I saw the man himself” are more emphatic than “I saw the man”.

Emphatic Pronouns can never stand alone as subjects. (Emphatic Pronouns subject রূপে একা বসতে পারে না । )

Hence it is incorrect to write: “His brother and myself were present”. “I will do it”. But we can write,

His brother and I myself went there.
I myself will do it.

An Emphatic Pronoun may refer to a person who is not the doer of the action e.g., I saw the minister himself, whereas a Reflexive Pronoun invariably denotes a person who is the doer as well as the person affected by the action, e.g.,

The boy hid himself inside the bush (object of a verb).
Sumona looked at herself in the mirror (object of a preposition).
He thinks little of himself (object of a preposition).

Chapter 2 Pronouns Distributive Pronouns

Each, either, and neither are called Distributive Pronouns because they separate one person or thing from a group.

(Each, either 3 neither লোক বা বস্তু থেকে পৃথকভাবে বোঝায় বলে তাদেরকে Distributive Pronoun বলে।)

I gave a book to each of the boys.
Either of them may go.
Neither of them was present.

Either and neither are always used by two persons or things.

Either means one or the other of the two.
Neither means ‘none of the two’.
Each is used of any number, say two or fifty: Each of the two or ten boys was fined.
Distributive Pronouns take singular pronouns and verbs:
- Neither of them is ill.
- Each of the girls has done her work.

Chapter 2 Pronouns Reciprocal Pronouns

Each, other, and one another are called Reciprocal Pronouns (Reciprocal = পারস্পরিক).

Each other is generally used when two are referred to, one another when more than two are referred to. ( দুয়ের মধ্যে পরস্পরকে বোঝাতে each other. এবং দুয়ের বেশীর মধ্যে পরস্পরকে বোঝাতে one another ব্যবহৃত হয়।)

Dutta and Sharma struck each other.
The boys fought with one another.

আজকাল অবশ্য দুয়ের মধ্যেও পরস্পরকে বোঝাতে one another ব্যবহৃত হয়।

Relative Pronouns
Look at the following sentences:
He is a boy. He stood first in the examination.
This is a house. My father built it last year.

Now see how these sentences have been joined by using the words who and which:

He is the boy who stood first in the examination.
This is the house which was built by my father last year.

Who and which here refer to “boy” and “house” respectively and they are used to connect the sentences. Who and which here are Relative Pronouns.

(উপরের sentence গুলিতে who এবং which যথাক্রমে boy এবং house-এর পরিবর্তে বসে sentence গুলিকে যুক্ত করেছে। এইক্ষেত্রে who এবং which Relative Pronoun)

A Relative Pronoun is a word that not only refers to some Noun or pronoun mentioned before but also joins two sentences or parts thereof.

The principal Relative Pronouns are who, which, that, and what. As and but are also used as Relative Pronouns.

The word to which the Relative Pronoun refers is called the Antecedent. (Relative Pronoun যার পরিবর্তে বসে তাকে Antecedent বলে।)

The book which you gave me is lost.
I want the boy who came to see me.

In the first sentence, the book is the antecedent of which. In the second sentence, the boy is the antecedent of who.

Uses of Relative Pronouns:

Declension: Who and which are declined as follows: that is not declined.

Singular and Plural – Singular and Plural

Nom. – Who – Which
Poss – Whose – of which (also rarely, ‘whose’) Which
Obj – Whom – Which

The uses of who (subject) and whom (object) are very often confused.

Carefully note their usage:

The man who (not whom) came here was my uncle.
I know Mr. Sarkar who (not whom) is a big businessman.
He is a person whom (not who) you can trust.
He is a person who (not whom) is quite trustworthy.
Who (not whom) do you think has done it?
Please tell me whom (also, who) I should speak to.
These are the boys whom (not who) I saw there.
These are the boys who (not whom) were present there.

Uses of ‘who’ and ‘which’:

Restrictive- Who and which have a restrictive force when they limit or define the meaning of an antecedent?

This is the boy who did it.
This is the book which I bought.

Continuative, Co-ordinate, or Conjunctive – Who and which have sometimes a continuative force and are used only to make some additional statement about the antecedent.

They may then be replaced by a conjunction and a pronoun:

You must obey your parents, which (= and) will win you the love of others.
I saw your father, who (= and he) recognized me.

No ‘comma’ is generally placed before the Relative Pronoun when it is used in the restrictive sense; but when it is used in a continuative sense, it generally takes a comma before it.

That is always used in a restrictive sense. It is used instead of “who” and “which”: After adjectives in the superlative degree:

He is the best man that I ever saw.

After some, any, all, only, one, etc. that require a defining clause after them: Is this the same that (also, as) you showed me before?

All that I want is this.
He is the only boy that did it.
Answer any that you can.

After the Interrogatives who and what:

Who is the boy that did it?
What is it that you want?

After two antecedents, one requiring who and the other which:

Many are the men and countries that I saw.

As is a Relative Pronoun when it comes after the same, such, as much, as many, and is applied to both persons and things:

This is the same book as that. Only such boys as have passed need apply.
I gave him as much (or as many men) as he required.

The same is also followed by that:

This is the same book that I lost.

But is used as a Relative Pronoun when it means not (=). It has a negative sense and is used after a negative word.

There is no man but (who not) wishes to be happy.

Relative Pronouns agree in number, gender, and person with their antecedents:

I who am your master say so.
You are the person (or persons) who is (or are) guilty.
This is the lady who lost her ring.
It is useless to me who am ill.

Omission of a Relative Pronoun: The Relative Pronoun is often omitted when it is the object of a verb or of a preposition:

He is the man (whom) I saw.
The book (which or that) I bought is lost.
I can remember the day (on which) he came.

A noun or pronoun in the Possessive Case should not be used as the antecedent to a Relative Pronoun. (Possessive case- noun pronoun Relative Pronoun-4 antecedent ).

Thus, instead of writing, “I went to the man’s house who is my friend”, we should write, “I went to the house of the man who is my friend.”

Chapter 2 Pronouns Interrogative Pronouns

Interrogative Pronouns who, which, what, whose, and whom, ask questions:

Who are you?
Whom do you want?
What do you want?
Which is the house?
Whose book is this?

They are also used to ask indirect questions:

Tell me what you want.
I asked who he was.

The difference in use:

Who is applied to persons (f), and is indefinite: Who goes there (i.e., the person is not known)?
Which is applied to both persons and things (3), and refers to one out of a group : (একটি group-এর মধ্য হতে কোনো একটি বা কয়েকটি নির্দেশ করে।): Which of these do you want?
What is applied to things, and a person’s profession: What do you want? What is he ?-He is a doctor.

Note carefully the following distinctions:

Who is he? -enquires about the name or parentage of the person.

The answer should be of the form – He is Sri Ramesh Chandra Bose; or, He is Ramesh, my son; or, He is Ramesh, of whom I spoke to you.

What is he? – enquires about the profession or social status answer should be of the form – He is a merchant or a teacher.

Which is he?– The wants him to be pointed out from a definite group (সম্মুখে উপস্থিত দলের ?).

The answer should be of the form – He is the man on the extreme right, or with a red shirt on, etc.

The Interrogative is often used in exclamation in the sense of ‘how great’: What folly! What a clever boy are you!

Chapter 2 Pronouns Indefinite Pronouns

Indefinite Pronouns do not point out any particular person or thing like the Demonstrative but refer to persons in a general manner (কোনো ব্যক্তি বা বস্তুকে না বুঝাইয়া They are any, one, some, other, another, many, all, they, none, few.

Look at the following sentences:

One should take care of one’s health. Some of the boys were present there.
They say a war will break out.
None can do it.
I know a few of them.

Any, as a Pronoun, is used only in interrogative and negative sentences.

It may be both singular and plural and may refer to both persons and things.

Have you seen any man (or men), or dog (or dogs) there? No, I have not seen

I want a few chairs; can you give me any?

Some, as a Pronoun, is plural and may be used for both persons and things: Some say, he will come.

He has many books; some are new, some old.

One-As an Indefinite Personal Pronoun, one is always followed by one, one’s, and one (in the nominative, possessive, and objective), and not by he, his, and him.

Thus:

One must do one’s duty. One does not know when one will die.

When every or no stands before one, use he, his, or him after it. Everyone did his duty. No one knows when he will die.

WBBSE Solutions For Class 9 English Functional Grammar Chapter 1 Sentences Phrases And Clauses Parts Of Speech And Nouns

January 17, 2025July 20, 2023 by vasantha

Chapter 1 Sentences

A sentence is a word or a group of words giving a complete sense. (যে শব্দ বা শব্দসমষ্টি একটি পূর্ণ অর্থ প্রকাশ করে তাকে sentence বা বাক্য বলা হয়।)

In the following examples, the groups of words on the left are not, because they do not make complete sense; but those on the right do so, and hence, they are

Did it – I did it.
Can do – I can do it.
In the garden – he is walking in the garden.
A good boy – he is a good boy.

In writing, the beginning and end of a sentence are indicated respectively by a capital letter and by a full stop, or a note of exclamation or interrogation.

A sentence may consist of one or more words. The one-word is, as a rule, intelligible only in connection with a particular situation. As:

In exclamations-good! What!
In imperatives-wait. Stop.

Assertive: these make simple statements (কোনো কিছু সাধারণভাবে ব্যক্ত করা হয়). As :

I know him.
He reads in class vii.
The boys love to play.

Interrogative: these ask questions (প্রশ্ন জিজ্ঞাসা করাহয়). As :

Why is he here?
What are you doing?
Will he come?

Read And Learn More WBBSE Class 9 English Functional Grammar

Imperative: these express commands, requests, etc. (এইসব বাক্যে কোনো আদেশ, উপদেশ, অনুরোধ ইত্যাদি বোঝায়). As :

Go away from here.
Don’t do this.
Please tell me your name.

Optative: these express wishes, prayers, etc. (কোনো ইচ্ছা, প্রার্থনা, আশীর্বাদ প্রভৃতি প্রকাশ করে). As :

God bless you.
May he live long.
Heaven help us.

WBBSE Solutions For Class 9 Fundamentals Of History	WBBSE Class 9 English Functional Grammar
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Exclamatory: these express sudden feelings or emotions (এইসব বাক্য দুঃখ, আনন্দ বা মনের কোনো আকস্মিক আবেগ প্রকাশ করে). As :

How nice!
Alas! He is no more.
What a fool you are!

May be further subdivided into two- (1) affirmative (-) and (2) negative (-).

WBBSE Solutions For Class 9 English Functional Grammar Chapter 1 Sentences Phrases And Clauses Parts Of Speech And Nouns

Affirmative are those that affirm something:

I know him.
He reads in class vii.
Go away from here.
May he live long?
How nice!

Negative are those that negate or deny something:

I do not know him.
He does not read in class vii.
Do not go away from here.
May he not suffer.
Alas! He is no more.

Some make a different division. They classify Sentences as follows:

Statements which simply affirm or deny something (হ্যাঁ বা না-সূচক সাধারণ বক্তব্য বোঝায়):

I know him.
He has not come today.

Questions which ask questions:

Why is he here?
Why did you not come yesterday?

Desires which contain some desire, order, or request (, ), etc:

May he live long?
Do not go there.
Please come here.

Exclamations which express a sudden feeling or emotion (প্রকাশ করা হয়) :

How nice!
Alas! I am undone.
And language functions
Convey different messages depending on their functions.

Functions may be broadly listed as:

(বিভিন্ন sentence-এর মাধ্যমে বিভিন্ন প্রকারের বক্তব্য প্রকাশিত হয়। sentence-এর এই বক্তব্যের রূপনানা রকমের হয়। )

Reporting
Asking for
Ordering
Thanking
Confirming
Something
Expressing
Sorrow information
Making suggestion
Guessing
Giving warning
Comparing
Regretting
Making statement
Assuring
Narrating an event
Greeting
Enquiring
Denying something
Expressing surprise
Describing
Advising
Describing a process
Requesting
Threatening something
Expressing doubt
Offering information
Demanding an action
Defining
Illustration
Expressing a sudden feeling, etc.
Expressing joy

Look at the following and their functions:

WBBSE Solutions For Class 9 English Functional Grammar Chapter 1 Sentences Phrases And Clauses Parts Of Speech And Nouns Functions and sentences

Chapter 1 Sentences The Subject And The Predicate

Every sentence can be divided into two parts, the subject and the predicate:

WBBSE Solutions For Class 9 English Functional Grammar Chapter 1 Sentences Phrases And Clauses Parts Of Speech And Nouns the subject of peridicate

The subject must be a noun or noun-equivalent and is found as an answer to the question what? Or who? Asked before the main verb.

Look at the following:

Noun: ramen went there. (Who went there ?)
Pronoun: she is a good girl. (Who is a good girl?)
Gerund: walking is good exercise. (What is a good exercise ?)
Infinite to. Tell a lie is a sin. (What is a sin ?)
Noun clause: why he did this is a puzzle. (What is a puzzle ?)

The subject usually comes at the beginning, but it may come in the middle or at the end of a sentence. Note the following :

He reads in class 8.
Though poor, he is honest.
For a long time, they whispered.
The best boy amongst them was Sandip.
The subject is often understood in some, especially in imperative ones.
Thus, go there = go you there. Sit down = sit you down. In analyzing such, the subject has to be supplied.

Chapter 1 Phrases And Clauses Phrases

He came to see me.
This is a chain of gold.

In the above, the groups of words written in italics do not make complete sense.

They do not have any subject or predicate and do not contain any finite verb, expressed or understood, but are used as single parts of speech.

In the first sentence the words ” to see me” act as an adverb to “came”; in the second sentence the words, “of gold” qualify the noun “chain” and thus act as an adjective; in the third sentence the words “on the table” are adverb qualifying “put”.

These groups of words are called phrases.

A phrase is a group of words that does not make complete sense, and does not contain a finite verb, expressed or understood, but is used as a single part of speech.

(যে শব্দ সমষ্টির নিজের কোনো finite verb নেই, এবং যারা পূর্ণ অর্থ প্রকাশ করে না, শুধু একটি single part of speech-এর মতো ব্যবহৃত হয়, তাকে phrase বলে।) agle part.

Phrases are of six kinds:

Noun phrase: It does the work of a noun.

He likes to play.
Walking is a good exercise.

In the first sentence, the phrase “to play” is the object of the verb “likes”. In the second sentence, the phrase “to walk” is the subject of the verb “is”. The groups of words here thus do the work of a noun and hence they are noun phrases.

Adjective phrase: It does the work of an adjective.

Hiren is a man of wealth.
The boys in the class stood up.
The book on the table is mine.

The phrase “of wealth” tells us what sort of man ‘Hiren’ is. It qualifies the noun ‘man’ just as an adjective does. It, therefore, does the work of an adjective. Similarly, the phrases “in the class”, and “on the table” are adjectives of ‘boys’ and ‘book’ respectively.

Adverbial phrase: it does the work of an adverb.

He came to see me.
He worked with care.
He fell from the tree.

The italicized phrase “to see me” tells us why ‘he’ came. It, therefore, does the work of an adverb and is an-adverbial phrase. Similarly “with care” and “from the tree” are adverbs qualifying “worked” and “fell” respectively.

Prepositional phrase: it does the work of a preposition.

He stood in front of me.
He could not come on account of illness.
The italicized phrases are prepositions for the objective cases “me” and “illness”.

Conjunctional phrase: it does the work of conjunction.

Come as soon as you can.
We went there in order that we might see him.
The phrase “as soon as” joins the two clauses “come” and “you can”.

The phrases “in order that” joins the two clauses, “we went there” and “we might see him.” They are all conjunctional phrases. Interjectional phrase-does the work of an interjection: what a pity! By Jove! Good heavens!

Chapter 1 Phrases And Clauses Clauses

I know that he is ill.
The boy who did it is my brother.
I went after he had gone.

The groups of words in italics in the above contain subjects (he, who, he respectively) and predicates (is ill, did it, had gone respectively) of their own, but form parts of bigger ., Such groups of words are called clauses.

A clause is a group of words having a subject and a predicate of its own, but forming part of a bigger sentence. (যে শব্দ সমষ্টি এক একটি sentence গঠন করে কারণ এতে subject ও predicate আছে, কিন্তু সেটি বৃহত্তর একটি sentence-এর অংশ মাত্র। )

Chapter 1 Parts Of Speech

Words are generally divided into eight classes or parts of speech according to the work they do in a sentence:

A noun is a word that names any person or thing:

(কোনো ব্যক্তি বা বস্তু বা বিষয়ের নামকে noun বলে।) man, book, gold, india, country, sweetness, honesty, air.

An adjective is a word which adds something to the meaning of a noun: ( যে word দ্বারা noun-এর কোনো গুণ, দোষ, অবস্থা, সংখ্যা, পরিমাণ ইত্যাদি বোঝায় তাকে adjective বলে। )

He is a good boy.
This is a dark room.
Give me a little milk.
Many men were present.

A pronoun is a word used for a noun or a clause:

(Noun বা clause-এর পরিবর্তে যে word বসে তাকে pronoun বলে।)

Ram is not here; he is ill.
He failed, which broke his heart.

A verb is a word used to express action, a state of being, or having something. ( যে word কোনো ব্যক্তি বা বস্তুর কোনো কিছু করা, হওয়া কিংবা থাকা বোঝায় তাকে verb বলে।)

he walks.
I go.
The sun shines.
The rose smells sweet.
He is tall.
I have a car.

An adverb is a word that generally adds something to the meaning of a verb, an adjective, or another adverb:

( যে word কোনো verb, adjective বা অন্য কোনো adverb-এর সম্বন্ধে কিছু বলে কিংবা তাদের অর্থ সীমাবদ্ধ করে তাকে adverb বলে। )

He walks fast.
He is very clever.
He did it quite easily.

A preposition is a word placed before a noun or a pronoun to show its relation to ‘some other word in the sentence:

(যে word noun বা pronoun-এর পূর্বে বসে sentence-এর অন্য কোনো word-এর সাথে এই noun বা pronoun- এর সম্বন্ধ বুঝিয়ে দেয় তাকে preposition বলে।)

The book is on the table.
He came to me.
She is in the garden.

A conjunction is a word that joins words or phrases or clauses:

(যে word অন্য words বা phrases বা clauses কে যুক্ত করে তাকে conjunction বলে।) he said this to Ram and Shyam.

He sat behind you but in front of me.
As he was ill, he did not go to school.

An interjection is a word which expresses some sudden feeling or emotion: (যে word মনের আকস্মিক উচ্ছাস বা ভাব প্রকাশ করে তাকে interjection বলে।)

Alas! Hello! Bravo!

Chapter 1 Nouns Classification

Nouns are of five different kinds:

WBBSE Solutions For Class 9 English Functional Grammar Chapter 1 Sentences Phrases And Clauses Parts Of Speech And Nouns classification

A concrete noun is the name of an object of sense, that is, an object which can be seen, touched, heard, smelt or tasted. ( যা দেখা যায়, স্পর্শ করা যায়, শোনা যায়, খাওয়া যায় অর্থাৎ যা ইন্দ্রিয়গ্রাহ্য তাইই concrete noun.)

Boy, dog, song, flower, milk.

An abstract noun is the name of a quality, action, or state belonging to an object. (যে noun দ্বারা কোনো মানুষ বা জিনিষের গুণ, অবস্থা, প্রকৃতি প্রভৃতি বোঝায়—মানুষ বা জিনিষকে বোঝায় না, তাকে abstract noun বলে।)

Softness, smile, wealth, silence.

A proper noun is the name of one particular person, place, thing, or event (or group of persons or places) as distinct from every other.

(Proper noun দ্বারা একটি নির্দিষ্ট প্রাণী, জায়গা, বস্তু বা ঘটনার নিজস্ব নাম বোঝায়।

Ramesh -the ganga
Kolkata -the himalayas
The french revolution- the ramayana
the hindus

A common or class noun denotes no one person or thing in particular but is common to any and every person or thing of the same kind.

[Common noun দ্বারা এক জাতীয় প্রাণী বা বস্তুর কোনো নির্দিষ্ট একটিকে না বুঝিয়ে তাদের সকলকেই বোঝায় (common = সাধারণ)। ] Man (not any particular man, but any and every man).

Book (not any particular book like the bible, the Vedas, the koran, etc., But any and every book).

River (not any particular river like the Ganga, or the Jamuna, but any and every river). Country (not any particular country, but any and every country) are common nouns.

Difference between a proper noun and common noun (proper no uncommon noun-এর মধ্যে পার্থক্য)

City বলতে আমরা যে কোনো শহরকেই বোঝাই। কিন্তু kolkata বলতে আমরা কেবলমাত্র kolkata city-কেই বোঝাই। এই ক্ষেত্রে city—common noun; কিন্তু kolkata —

Proper noun : এইরূপ :—

Proper – Common

The ganga- river
The gita- book
India -country
Indian ocean-ocean
Monday -day
B.t. Road- road

There are a few nouns, generally classed as common, which are sometimes called singular nouns because there is only one of each of them known to us

Earth, sun, moon, etc.

When god and lord refer to the almighty, they are proper; but when they refer to the different gods of mythology and temporal lords, they are common.

A collective noun is the name of a group or collection of persons or things taken as a whole.

(যে word দ্বারা একই প্রকারের অনেকগুলি প্রাণী বা জিনিষের সমষ্টি বোঝায়, স্বতন্ত্রভাবে তাদেরকে বোঝায় না তাকে collective noun বলে।)

Thus, in “a flock of sheep” “sheep” is a common noun, because it stands for any and every sheep; but flock is a collective noun, because it stands for all the sheep referred to, taken together, and not any one sheep taken separately. Similarly, in “an army of soldiers”, and “a crowd of people”, army and crowd are collective nouns, as they stand respectively for all the soldiers and people referred to, taken together.

(“Flock of sheep” এই বাক্যাংশে “sheep” কথাটি common noun, কারণ সেটি ভেড়ার সাধারণ নাম ; কিন্তু flock কথাটি collective noun, কারণ তা কতকগুলি ভেড়ার সমষ্টিকে বোঝাচ্ছে। এইরূপ, “crowd of men”, “army of soldiers” crowd army collective nouns, men and soldiers-এর সমষ্টিকে বোঝাচ্ছে।)

A collective noun takes a singular verb when the things and persons are taken collectively, and a plural when they are taken separately.

(Verbটি singular হয়; সকলকে সমষ্টিভাবে না বুঝিয়ে স্বতন্ত্রভাবে বোঝালে verbটি plural হয়।)

The audience is requested to take their seats.
The class is large.

But we must be consistent. Thus, we must write :

The board has agreed to grant bonuses to its (not, their) employees.
The mob does (not, does) not know their mind.

Chapter 1 Nouns A list of collective words

An army or regiment of soldiers
A band of robbers, musicians
A bouquet of flowers
A bevy of beauties, women
A bundle of rags, sticks, and firewood, lies
A bunch of keys, grapes, flowers a brood of chickens
A board of directors
A chain of events, mountains
A class of students, persons
A clump of trees.
A cloud of locusts
A cluster of grapes, islands, stars
A consignment of goods
A course of lectures
A crew of sailors
A crowd of people
A curriculum of studies
A drove of cattle (cattle being driven), sight-seers
A fleet of ships
A flight of birds or steps
A flock of sheep (generally small animals), geese
A gang of thieves, robbers
A galaxy of stars
A group of islands
A grove of trees
A herd of cattle (generally big animals), deer, elephants
A hive of bees
A heap or mass of ruins
A horde or tribe of Arabs
A litter of pups, pigs
A pack of hounds, wolves, cards, thieves, liars, lies
A pair of shoes
A Parliament of Owls
A pile of books
A pride of Lions
A range of mountains
A series of events
A stack of hay, wood
A shoal of fish
A shower of rain, arrows
A swarm of bees or flies.
A suit of clothes

A material noun denotes the matter or substance of which things are made.

It is also called the mass noun. (যে material বা পদার্থ দ্বারা কোনো জিনিষ গঠিত হয় তাকে material noun বলে।)

Thus, the river is a common noun, but water, of which it is made, is a material noun; sheep is a common noun, but mutton, the flesh of a sheep, is a material noun.

Chapter 1 Nouns Countable And Uncountable Nouns

Nouns can also be classified generally as countable and uncountable: countable nouns stand for something that can be counted (যা এক, দুই করে গণনা করা boy, egg, school, man, tree, house, etc.

Only, countable nouns have plural forms and can be used with the indefinite article an) in the singular or many, few, a few, several, etc.

In the plural: (countable singular noun- এর পূর্বে a, an, এবং plural noun-এর পূর্বে many, few, a few, several ইত্যাদি বসে।) a school, a boy, an umbrella, many cows, a few books.

Uncountable nouns stand for something that cannot be counted though they can be measured (যা এক, দুই করে গণনা করা যায় না কিন্তু যা পরিমাপ করা যায়) :

Water, air, glass, wood, sand, etc.

Such nouns have no plural form and are not used with the indefinite article (a/an). (4 কোনো plural form নেই এবং এদের পূর্বে a বা an বসে না।). They are preceded by much, little, etc.

(এদের পূর্বে much, little ইত্যাদি ব্যবহৃত হয়) to denote amount or quantity: much money, little water.

Some of these can, however, be both countable and uncountable according to the context in which they are used, with a change in their meaning.

কোনো কোনো ক্ষেত্রে এরা countable এবং uncountable উভয়ভাবেই ব্যবহৃত হতে পারে। সেক্ষেত্রে তাদের অর্থ ভিন্ন প্রকারের হয়।)

Paper =the substance on which we write (uncountable)
A paper = a newspaper (countable)
Glass = the material (uncountable)
A glass = a tumbler (countable)
Wood = The table is made of wood. (Material, uncountable)-কাঠ
A wood forest the bungalow is in the middle of a wood. (Countable)
Copper = metal (uncountable)
A copper = coin (countable)

Notice how often we put a piece of, a great deal of, a bit of, etc. Before uncountable nouns when we want to “individualize” them. We also use some when we want to indicate an indefinite quantity.

Note the following examples:

A bit of string (এক টুকরো সুতো) -some string (কিছু সুতো )
A piece of (bar) soap- some soap
A piece of work (কাজের অংশ)-some work
A lump of sugar (সামান্য একটু চিনি)-some sugar
A piece of advice (সামান্য পরামর্শ)-some advice
A flash of lightning (বিদ্যুতের খানিক চমক- some lightning
An act of cruelty-some cruelty
A piece of news (সংবাদ টুকু)-some news
A piece of furniture-some furniture
A piece of luggage-some- luggage
A piece of music-some music

Chapter 1 Nouns Number

In English, there are two numbers: singular and plural. When one thing is spoken of, the noun is singular, such as a boy, a girl, or a cat. But when more than one thing is spoken of, the noun is plural, such as boys, girls, and cats.

Rules for forming the plural:

Most nouns form their plural by adding s to the singular:

(Singular noun-এর শেষে সাধারণত s যোগ করে plural হয়।)

Singular – plural
Girl- girls
Eye- eyes
House- houses
Book- books
Ant- ants
Table- tables
Car- cars
Chair- chairs
Cat- cats
Pen- pens
Cow- cows
King- kings
Dog- dogs
Tree- trees
Bird- birds
Pencil- pencils
Doll- dolls
Leg- legs
River- rivers
Room- rooms
Brother- brothers
Lion- lions
Sister- sisters

Nouns ending in s, ss, sh, ch (soft), x, and z take es in the plural: (যে সব singular noun-এর শেষে s, ss, sh, x, 2 ও soft ch অর্থাৎ যে ‘ch’ -এর উচ্চারণ ‘চ্’-এর মত থাকে তাদের শেষে es যোগ করে plural হয়।)

Singular – plural
Gas- gases
Box- boxes
Fox- foxes
Fish- fishes
Watch- watches
Monarch -monarchs
Branch – branches
Topaz- topazes

But when ch is pronounced as k, only s is added: ( যদি ch -এর উচ্চারণ ‘ক’-এর মত হয় তবে শুধু s যোগ করে plural হয়।)

Singular – plural
Monarch – monarchs
Stomach -stomachs

Nouns ending in y preceded by a consonant or qu change y into and add es in the plural: (যদি noun-এর শেষে y এবং তার পূর্বে consonant অথবা qu থাকে, তা হলে plural করবার সময় y কে I করে পরে es যোগ করতে হবে।)

Singular- plural
Lady-ladies
City-cities
Army-armies
Country-countries
Copy-copies
Body- bodies
Soliloquy (off) soliloquies
Sky- skies
Baby- babies
Fly- flies

But if y is preceded by a vowel, add only যদি y– এর পূর্বে vowel থাকে তবে শুধু s যোগ করে plural হয়।) but safe-safes; strife-strifes; thief- thieves.

Some take both forms: staff-staffs (), staves (sticks); wharf (g)—wharves, wharves; scarf (a)- scarfs, scarves.

Nouns ending in ‘o’ preceded by a consonant generally take es in the plural: (যদি noun-এর শেষে ০ থাকে এবং তার পূর্বে consonant থাকে, তবে সাধারণত es যোগ করে plural হয়। )

Singular- plural
Hero -heroes
Mango -mangoes
Buffalo- buffaloes
Potato- Potatoes
Volcano- volcanoes
Mosquito- mosquitoes

Exceptions- canto-s, halo-s , piano-s, manifesto-s, photo-s, memento-s, dynamo-s, portico-s.

Nouns ending in ‘o’ preceded by a vowel generally take only s in the plural: (যদি noun-এর শেষে ০ থাকে এবং তার পূর্বে vowel থাকে, তবে সাধারণত s যোগ করে plural হয়।)

Singular – plural
Bamboo – bamboos
Radio -radios
Cuckoo- cuckoos
Folio- folios

Some nouns form their plural by change of vowels: (কতকগুলি noun-এর word-এর মধ্যেকার vowel-এর পরিবর্তন করে plural করতে হয়।)

Singular – plural
Man- men
Louse (উকুন)- lice
Woman- women
Mouse- mice
Foot- feet
Goose (রাজহাঁস)- geese
Tooth- teeth

Some nouns adden: (কতকগুলি noun-এর শেষে en যোগ করে plural করা হয়। )

Singular – plural
Ox – oxen
Child – children
Brother- brethren (also brothers)
Nouns that have no plural forms:
(এইসব noun-এর কোনো plural form: নাই, এরা সর্বদাই singular রূপে ব্যবহার হয়।)
Alphabet (বর্ণমালা)
Expenditure (ব্যয় )
Furniture (আসবাবপত্র)
Information (সংবাদ, খবর)
Luggage (মালপত্র)
Offspring (child or children)
Poetry
Scenery (দৃশ্য)

He has learned the alphabet. He has sold all his furniture or luggage. All his expenditure is shown here. These are my offspring. I got all the information I wanted.

These flowers by the riverside are beautiful scenery. He writes good poetry.

Nouns which have no singular forms: (এইসব noun-এর কোনো singular হয় না, সর্বদাই plural form-এ ব্যবহার হয়। )

Jeans (জিন কাপড়ের প্যান্টালুন)
Alms (ভিক্ষা)
Amends (ক্ষতিপূরণ
Annals (ইতিবৃত্ত)
Ashes (ছাই)
Assets (সম্পত্তি)
Auspices (প্রসাদ, আনুকূল্য
Bellows (হাপর )
Scissors (কাঁচি)
Shears (কাস্তে)
Shorts (খাটো প্যান্ট)
Spectacles (চশমা)
Thanks (ধন্যবাদ) )
Wages (বেতন)
Bowels (অন্ত্র)
Eaves (ঘরের ছাঁচ
Billiards (একরকম খেলা) proceeds (আয়)
Dregs (তলানি)
Entrails (নাড়িভুঁড়ি)
Fetters (শৃঙ্খল
Forceps (চিমটা)
Measles (হাম)
Mumps (গালফুলা রোগ) nuptials (বিবাহ)
Odds (ন্যূনাধিকভাবে তারতম্য) pyjamas (পাজামা)
Paints (রং)
Tidings (সংবাদ)
Tongs (চিম্‌টা)
Vitals (জীবনী শক্তি

Nouns which have the same form in both the numbers:

Apparatus, common, corps, deer, innings, means, picé, public, series, sheep, species, swine, and the nouns of number, weight or money such as dozen, score, yoke, stone (weight), hundred weight, when used after a numeral, especially if they join with that numeral to make a compound adjective (as in ‘two-ton lorry’).

The singular meaning is expressed by putting a singular adjective, such as a, an, one, this, that, etc. Before them.

A deer, one sheep, this piece; but, two deer, two-piece.

The words hundred, thousand, lakh (or, lac) million, dozen, score when preceded by a definite numeral (পূর্বে নির্দিষ্ট সংখ্যাবাচক শব্দ থাকলে) or by several or a few are never made plural:

I want three hundred (or, one hundred) rupees.
Five thousand (not, thousands) men assembled there.
He bought one (or two) dozen pencils.
Draw a cheque for rupees three lacks (or lac). (Not, lakhs or lacs).
A few hundred people collected there.
Give me five score eggs.
Several hundred (or dozen) eggs were damaged.
Three million (not, millions) tons of rice have been imported this year.

But when these words are not preceded by numerals and used ‘merely to convey the idea of a large number or are preceded by some, many (অনির্দিষ্ট সংখ্যাবাচক শব্দ পূর্বে থাকলে), they are made plural

Some dozens, many dozens, hundreds of people, thousands of ants, scores of animals, many thousands, millions of rupees, lacs, and lacs of rupees, etc.

The plural of compound nouns (except nouns ending in full and fall) is generally formed by adding s to the important word; as:

Governors-general (governors-general is also used); passers-by; brothers-in-law; on-lookers; but mouthfuls, handfuls, pitfalls (5), waterfalls (2).

In nouns ending in ‘man’, the plural is formed by changing man into man when a man is used in the sense of a human being; such as Englishmen, nobleman, or workman.

When, however, the final man does not mean a human being, but is a part of the word itself, the plural is formed by adding s only; as germans, Mussalmans, and Brahmans. “Mankind. The singular number, referred to by it and its, not they and their.”- Usage by f.t. Wood.

Plurals of letters of the alphabet and of numbers are formed by adding (s): b.a.’S d.d.’ S.
Cut your t’s and dot your I’s; 3’s, 5’s, etc.
Some add only s in the plural, leaving the apostrophe for the genitive.
He hit two 4’s (4s) and two 6’s (6s).
Three b.a.’S (b.a.s) and two m.a.’S (m.a..s) were selected.

Plurals of abbreviations:

Single letters are doubled:

Pp. For pages, ll. For lines, mss. For manuscripts.
Curt forms take s: secs. For sections, etc.

Miscellaneous:

Singular- plural
Mr- Messrs
Mrs madam- mesdames
Mrs brown – miss brown
The mrs browns – the miss browns the misses brown
Madam- ladies
Man-servant- master brown
The masters brown the master browns- mr brown
Messrs Browns- woman-servant lord-justice knight-templar
The Mr browns- men-servants
Women-servants- lords-justices
Knights templars

Foreign plurals:

Agendum (বিচাৰ্য- agenda
Singular crisis (সঙ্কটাপন্ন)
Crises বিষয়) অবস্থা )
Appendix – appendices
Analysis (বিশ্লেষণ)
Radius (ব্যাসার্ধ)
Radii- analyses
Erratum (শুদ্ধিপত্র)- errata
Axis (অক্ষ )- axes
Bandit (বোম্বেটে) – banditti (or bandits)
Focus (কেন্দ্র) – foci (or focuses)
Formula (সূত্র)- formulae
Basis (ভিত্তি)- bases
Medium (মাধ্যম)- media
Memorandum (স্মারকলিপি)- memoranda
Hypothesis seraph ( প্রথম শ্রেণির স্বৰ্গ-দূত) – hypotheses
Terminus (শেষপ্রান্ত ) – termini (or terminuses)
Phenomena- phenomenon
Seraphim (or seraphs)
Vertex (শীর্ষ) -vertices
Oases- oasis (মরুদ্যান)

The tendency of modern English is to reject all foreign forms.

The name of a country, or a thing, though plural in form, is treated as singular; as:

The united states of America is a rich country;
The folk tales of Bengal is a nice book.

WBBSE Solutions For Class 10 Physical Science And Environment Chapter 1 Concerns About Our Environment

January 17, 2025June 25, 2023 by vasantha

Chapter 1 Concerns About Our Environment Physical Science And Environment

Physical science explains the naturally occurring phenomena in our everyday life. With the advancement of industrialization, at present, the entire environment is under greater threat.

We are to know the reasons for the threats, as well as to be conscious of the remedial measures for sustaining life on the earth.

Wbbse Class 10 Physical Science Notes

Chapter 1 Concerns About Our Environment Structure Of The Atmosphere

The Earth is surrounded by a blanket of air called the atmosphere. It keeps the average temperature of the earth nearly constant.

The earth’s atmosphere extends up to a height of about 1600 kilometers from the surface of the earth.

WBBSE Notes For Class 10 Physical Science And Environment

The atmosphere is held near the surface of the earth by the force of gravity and it is made up of a mixture of gas molecules like N₂, O₂, CO₂, Ar, O₃, water vapors, and dust particles.

The density (mass per unit volume) and also temperature is not the same throughout the atmosphere at all heights.

Earth’s atmosphere can be divided into four major layers separated from one another due to changes in air temperature.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Physical Science And environment Sturcture of the Atmosphere

The layers are:

Troposphere,
Stratosphere,
Mesosphere and
Thermosphere.

Wbbse Class 10 Physical Science Notes

1. Troposphere: This is the layer where we all live in. It extends from the ground roughly 12 kilometers above the earth’s surface. About 80% of the total mass of the atmosphere is contained in this layer.

Almost all dust particles and water vapors are present in this layer, so all the weather phenomena like storms, clouds, rains, air currents, etc occur in this layer.

Components like O₂, CO₂, and N₂useful for sustaining life are available here.

WBBSE Notes For Class 10 Geography And Environment	WBBSE Notes For Class 10 History And Environment
WBBSE Solutions For Class 10 Life Science	WBBSE Class 10 Life Science Multiple Choice Questions
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WBBSE Notes For Class 10 Physical Science And Environment

The temperature in the troposphere is constantly changing and it falls with increasing altitude at an average rate of 6-5°C per kilometer of height above the earth’s surface.

The upper limit of the troposphere at which the temperature stops decreasing is called tropopause. The temperature at this level may be as low as – 56°C.

2. Stratosphere: It is the second layer of the atmosphere. Above the tropopause, it extends up to 45 km above the earth’s surface.

The tropopause separates the troposphere from the stratosphere.

There is very little air (N₂, O₂) but practically no moisture in this layer, so no cloud is formed here and disturbances like storms, and tornadoes do not take place here.

Due to this fact, the layer is calm and quiet. Jet planes fly through this layer as the stratosphere is free from all weather disturbances. Due to a lack of O₂, normal breathing is difficult in the upper levels of the stratosphere.

The farther side of the stratosphere is called the ozonosphere and this part contains most of the ozone (O₃) gas molecules of the atmosphere.

The O₃ molecules absorb most of the harmful UV rays of the sun and protect life on the earth. Thus, the ozonosphere acts as a filter.

The absorption of UV rays warms the stratosphere from – 56°C to 3°C. Here also temperature increases with the rise in altitude.

The end of the stratosphere where the temperature remains almost constant is called stratopause.

O₃molecules keep the upper layer of the stratosphere warm and it contains too little O₂. While in the lower part of the stratosphere, no UV light-all is absorbed by O₃molecules in the upper layer.

Wbbse Class 10 Physical Science Notes

WBBSE Solutions For Class 10 Physical Science And Environment Chapter 1 Concerns About Our Environment

3. Mesosphere: Above the stratosphere, the layer of atmosphere lying between 45-85 kilometers from the earth’s surface, is called the mesosphere.

In this layer, very little quantity of N₂, O₂, O₂, and NO₂ is present. In the mesosphere, the temperature drops again with altitude, reaching a minimum of 92°C.

It is the lowest temperature in the atmosphere. Thus, the mesosphere is the coldest layer. Because of the very low temperatures, ice crystals can be formed here.

It protects the earth from being struck by meteors. The upper end of the mesosphere where the temperature remains almost constant is called mesopause.

It acts as the boundary between the mesosphere and the thermosphere.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Physical Science And environment temperature vs height

4. Thermosphere: The layer of the atmosphere above the mesosphere extending about 85-500 kilometers above the earth’s surface is called the thermosphere.

It is the layer where the air is very very thin. There is nothing protecting this layer from the heat of the sun, that’s why its temperature increases with altitude up to about 1200°C.

Wbbse Class 10 Physical Science Notes

It has two different parts:

ionosphere
Exosphere.

1. ionosphere: The lower part of the thermosphere consists of ions of lighter atoms like NO+, O+, electrons, etc.

Because of the presence of ions, this particular zone becomes highly electrically conducting, making radio communications possible around the world. The northern lights or aurora borealis are seen here.

2. Exosphere: It is the upper portion of the thermosphere, extending somewhere about 500- 1000 kilometers above the earth, having traces of lighter gas molecules like H₂, He, etc.

The highest temperature of this layer is about 1200-1700°C. It is colder at night and much hotter during the day. Artificial satellites and space stations operate from this portion.

Beyond the exosphere, there is practically no air. It is almost a vacuum.

Variation of pressure with altitude: Normally, the pressure of the atmosphere is maximum at the lowest layer and it decreases as the height above the earth’s surface increases.

At the ground, the air pressure is about 1.013 atm (where 1 atm = 76 cm of Hg). The variation of pressure with altitude.

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Convection currents and storms: Consider the first 50 kilometers where 99% of the atmosphere exists. Sunlight passes through the atmosphere and warms the ground heating up the air adjacent to the earth’s surface.

It expands and becomes less dense. While the cold air from above sinks, it pushes up the warm air to take the vacant space.

This action sets up the flow of air which is called convection currents. Sea breeze, and land breeze flow due to the convection of air.

In liquids and gases, heat is transmitted by convection as their molecules are quite free to move about.

On the other hand, molecules in a solid, being closely packed, cannot move like molecules of liquids and gases. So, convection currents does not occur in solids.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Physical Science And environment Convention current.

All kinds of wind are caused due to uneven heating of the earth. When the air moves at a high speed over a surface, it results in decreasing pressure.

Thus, strong winds start blowing from the high-pressure area to the low-pressure area. This difference in air pressure results in the formation of a storm. Higher wind speed creates cyclones/tornados/typhoons/hurricanes.

Chapter 1 Concerns About Our Environment The Ozone Layer

Ozone (O₃) is an allotrope of oxygen. Its molecules are made up of 3 oxygen atoms bonded together. The ozone layer in the stratosphere absorbs most of the harmful UV rays coming from the sun and protects life on Earth.

Formation of the ozone layer: Ozone (O₃) is formed in the upper part of the stratosphere by a photochemical reaction of O₂.

UV-rays of small wavelength 240 nm on being absorbed by O₂ molecules in the stratosphere splits into 2 fast

Moving O-atoms. Each O-atom collides with air molecules (N₂, O₂) around them. This slows down the free O-atoms, and abling them to make bonds with O, molecules. In this way, O₃ molecules are formed.

Depletion of the ozone layer: O₃ molecules break down again by absorbing UV-radiation of high wavelength 300 nm and O₂ is back again.

The density of the ozone layer is measured by the Dobson unit (DU). 1 DU refers to the 0.01 mm thick ozone layer at STP.

In this way, O₃ is continuously formed and broken by UV light in the ozone-oxygen cycle. The thinning of the ozone layer in the upper atmosphere is called ozone layer depletion.

The main cause of it is the release of chlorofluorocarbons (CFCs mainly CF₂, CI₂, and CFCI₃) used in refrigeration, air conditioning, fire extinguishers, foam production, and aerosol sprays and also by nitric oxide (NO), nitrogen dioxide (NO₂).

The thickness of the ozone layer is thus reduced. The thinning looks like a hole, called the ozone hole. This was observed by scientists in the 1980s over Antarctica.

In the Montreal Protocol (an international treaty), on 1 January 1989, thirty nations worldwide agreed to reduce the usage of CFCs and encouraged other countries to do so.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment The ozone layer Ozone hole over antarctica.

Role Of Cfcs In The Destruction Of Ozone Layer:

CFCs are comparatively inactive in the lower atmosphere, but highly reactive in the stratosphere.

When CFCs are hit by photons, they break up into ‘free chlorine’ (CI) atoms which grab one of the atoms of the O₃ molecule.

As a result, O, molecules are broken down very rapidly (1 Cl-atom can break nearly 1000 no of O₃ molecules). This led to the depletion of the ozone layer.

Role Of No, No, In The Destruction Of Ozone Layer:

⇒ $\mathrm{NO}+\mathrm{O}_3 \rightarrow \mathrm{NO}_2+\mathrm{O}_2 ; \mathrm{O}_2 \stackrel{\text { UV-rays }}{\longrightarrow} \mathrm{O}+\mathrm{O}$

Sources of NO, NO₂ are supersonic jet planes, and nitrogenous fertilizers. Also, NO emitted from transportation oxidizes into NO₂. However, NO reacts with O₃ molecules in the stratosphere to form O₂and NO₂.

The O₂ molecules break down to atomic O by absorbing UV radiation. NO₂ reacts with atomic O and forms NO back.

So, the amount of NO remains the same. As a result, O molecules get decomposed. In this way, the concentration of ozone in the stratosphere is destroyed.

Effects of ozone depletion on living bodies: 4th Proof User 5 (ASHIS) For humans Direct exposure to UV radiation can lead to serious health problems like sunburn, skin cancer, skin aging, cataracts, weak immune system, etc.

For animals: Skin cancer, eye problems, etc.

For plants, UV rays can affect the photosynthesis process, growth rate, flowering, etc. As a whole, it can destroy the total life cycle.

For marine life: Zooplanktons and phytoplanktons (the base of the food web) are also affected by strong UV rays.

Chapter 1 Concerns About Our Environment Greenhouse Effect And Global Warming

The earth is getting an enormous amount of heat radiation from the sun in the form of UV, visible, and IR rays.

While passing through the earth’s atmosphere, the ozone layer blocks some parts of UV rays. The remaining rays reach the earth’s surface.

A part is absorbed by the earth and especially long wavelength IR-rays are reflected back. But some gases in the atmosphere, trap the heat radiation and obstruct to escape to space.

This leads to the warming up of the earth’s surface and also the atmosphere. This effect is known as the greenhouse effect.

The increase in the average temperature of the earth due to the greenhouse effect is known as global warming.

The gases involved in warming up the earth are known as greenhouse gases.

Question 1. Why it is called the greenhouse effect?
Answer:

Greenhouse effect

A greenhouse is a glass building in which plants that require protection from cold weather are kept. The glass cover traps all the heat radiation but cannot allow longwave IR rays.

So the inside environment keeps warm. For our planet Earth, the atmosphere acts as the glass cover and traps the heat.

Utility of greenhouse gases: If there were no greenhouse gases to trap the sun’s radiation, the temperature of the earth’s surface would have been -20°C~-30°C. It would have been impossible for the survival of living beings.

Greenhouse gases: The gas molecules of CO₂, H₂O vapor, CH₄, N₂O, CFCs, etc. absorb the sun’s IR radiation.

Among these, CO₂ is the main greenhouse gas. They trap too much heat and the earth becomes hotter and hotter.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Green house effect and global warming Causes of green house effect

Remember: N₂ and O₂ which form most of the atmosphere do not absorb IR radiation. So N₂ and O₂ are not greenhouse gases.

Causes of global warming: Both natural and human activities are responsible for the emission of greenhouse gases such as volcanic eruption, plants, forest fires, deforestation, smoke from vehicles & industries, etc.

Effects of global warming:

With the increase in the earth’s temperature, the glaciers melt faster than they accumulate new snow. As a result, the water level in oceans and seas rises up.

It causes flooding of lowlands, agricultural soil contamination with salt, soil erosion, etc.

From rising water levels more water vapors are evaporated-this leads to the formation of hurricanes/cyclones.

Because of global warming, birds, polar bears, and different insects migrate to move from one area to another.

Global warming helps mosquitoes to grow vigorously in tropical regions, and it causes the spread of diseases like dengue, chikungunya, malaria, etc.

How can we contribute to reducing global warming?:

Planting more and more trees, to decrease the emission of CO₂,
Using renewable energies like solar energy, wind energy, hydropower, etc.
Reducing the use of products that generate greenhouse gases.

Chapter 1 Concerns About Our Environment Calorific Value Of Fuels

Fuels are substances that can burn or which can undergo combustion in excess air (oxygen) such as coal, cow-dung cakes, matchstick, petrol, diesel, kerosene, alcohol, LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas), etc.

So, fuels can be solid, liquid, or gas. All the fuels produce heat on burning. But, different fuels produce different amounts of heat on burning.

Such a difference in producing heat energy i.e. fuel efficiency is expressed in terms of its calorific value. The quality of fuel depends on its calorific value.

The total amount of heat produced in kilojoule by complete burning or complete combustion of one kilogram (or one gram) of solid or liquid fuel in excess air (O₂) is called its calorific value.

It is expressed in the unit of ‘KJ per Kg’ or ‘KJ per g’. In the case of gaseous fuel, it is the total amount of heat produced by the complete combustion of 1 m3 of its volume at STP the calorific value of some common fuels.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Physical Science And environment fuels

7 Higher calorific value of fuel means that the more heat it produces on burning, the better fuel it is.

The necessity of conservation of fossil fuels: Most of our energy requirements are met by the burning of fossil fuels like coal, petroleum, and natural gas.

Today we use them carelessly, without thinking that fossil fuels are non-renewable sources of energy that do not develop in a day or two but rather will take millions of years to form.

If we continue to burn these fuels at this rate, it leads to an increase in CO₂ in the environment. This contributes to greenhouse gases and ultimately global warming.

So, the lesser would be the consumption, the lesser would be the pressure on the next generations.

Concept of sustainable development: Sustainable development refers to the development that will allow our future generations to lead a quality lifestyle same as what is being enjoyed by the current generation by utilizing all natural resources. We can use fossil fuels in fewer amounts only when required.

Harnessing alternate sources of energy for sustainable growth and development: Fossil fuels are non-renewable sources of energy. They are used in almost 90% of areas.

These, on combustion, produce harmful substances like C, CO, oxides of nitrogen (NO), oxides of sulfur (SO), soot, etc. which pollute the air around us.

Their stocks are also very limited. So, misuse of these fuels should be avoided.

Rather, we are looking for alternate or renewable or non-conventional sources of energy such as solar energy, wind energy, tidal energy, geothermal energy, biomass energy-biofuel, biogas, etc.

Solar energy: The Sun is the main source of all energy. The energy obtained from the sun is called solar energy.

WBBSE Solutions For Class 10 Chapter 1 Concerns About Our Environment Calorific value of fuels uses of solar panel.

Today scientists are able to make solar cookers, solar water heaters, and many other devices that work on solar energy.

A single solar cell can produce electricity on a very small scale. The solar cell is used in watches, transistors, calculators, and for domestic purposes in remote village areas. Solar batteries are used in space flight.

To obtain more electricity and more electric power, a large number of solar cells are joined together to form a solar panel.

These are used in artificial satellites, space stations, water pumps, street lighting, traffic signals, etc.

Wind energy: The energy obtained from very fast-moving wind is called wind energy. It is a natural, conventional, renewable source of energy.

It is available in high-wind regions without any cost. It also causes no pollution.

Nowadays high-speed wind energy is used in a wind turbine to generate electricity. The basic principle is here the same as any power plant. Here, the turbine is connected to the windmill.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Calorific value of fuels wind mill

As wind strikes the blades of the windmill, it starts rotating. Hence, the turbine and the generator start rotating and electricity is generated. Also, windmills are used to grind grains.

The working of a windmill depends on the speed of the wind.

Tidal energy: The energy obtained from rising tides in coastal areas is called tidal energy. It’s a renewable source of energy.

In general, it is not enough to generate electricity on a large scale with tidal energy.

But, it is harnessed for generating electricity by constructing a dam across a comparatively narrower opening to the sea.

Geothermal energy: It is the energy obtained from the heat of the core of the earth. In a few places, rocks under the earth’s surface remain very hot, and the heat turns underground water into steam which is compressed at higher pressure between the rocks.

Drilling holes through pipes into such places, steam is ejected through the pipes, which in turn, rotates the turbine to generate electricity.

In our country, Madhya Pradesh, there is one such power station.

Biomass energy: A mixture of waste materials like wood filings, crop residues, garbage, excreta of animals, sewage, dead parts of plants, trees, animals, etc is known as biomass.

It mainly contains carbon-rich compounds. The chemical energy stored in biomass is known as bioenergy or biomass energy. Biomass can be used as a source of energy.

For example-

Dry biomass, like cow dung cake, is burnt to produce heat energy, which is used for cooking purposes.

In biogas plants, cow dung and sewage are used to produce biogas. The residue is used as organic manure in the fields.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Calorific value of fuels Methanogenic bacteria

Biogas: It is prepared in biogas plants. When the slurry of cow dung and water (or a mixture of crop residue, sewage, or other waste materials) is allowed to make anaerobic fermentation in the absence of oxygen but in the presence of water,

They produce a mixture of methane, carbon dioxide, hydrogen, and traces of hydrogen sulfide. This mixture is called biogas.

The fermentation is carried out by anaerobic bacteria known as methanogenic bacteria which decompose the carbon compounds present in biomass (organic wastes) into methane gas and carbon dioxide.

Biogas is a renewable source of energy. It can never replace natural gas.

Uses: Biogas mainly contains methane (about 75%) which is an excellent fuel for cooking. It causes no environmental pollution. It can be used for street lighting and for running engines.

The waste products such as nitrogen and phosphorus left from biogas plants are used as fertilizers.

WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Calorific value of fuels A biogas plant

Advantages of using biogas as fuel:

On burning, biogas does not produce any smoke or ash, which can be used for domestic cooking. The calorific value of biogas is very high (about 35000-40000 KJ/Kg).

Electricity from waste:

Tons of organic waste, foods, and unsold vegetables in everyday market pollute our environment and are used to turn into electricity in biogas plants.

These wastes are converted into a slurry and put into a large container (pit).

Using an anaerobic digester, the waste is converted into biofuel and put into a biogas generator which converts it into electricity. This type of project can make life more sustainable.

Biofuel: It is a form of biomass energy produced from biomass. Its examples are bio-ethanol (liquid) and bio-diesel (gaseous like gobar gas).

Bio-Ethanol: It is an alternative to petrol in road vehicles. It is produced by the sugar fermentation process of sugarcane, corn, rice straws, wheat, etc.

Bioethanol is added to petrol to minimize environmental pollution. It is carbon neutral and produces fewer greenhouse gases.

Biodiesel: It is an alternative to diesel. It is manufactured by the transesterification process from vegetable oil, animal fats, or unused oils from households. Bio-diesel can be used as a blend with regular diesel.

Coal-bed methane or CBM: In coal mines, plenty of methane gas (>95%) remains adsorbed in hard layers of coal. It is called coal-bed methane (CBM).

It is formed during the process of coalification by the transformation of plants into coal.

The coal-bed methane is a form of natural gas extracted from the coal bed by drilling steel pipes 100 -1500 m deep below ground into the layers of coal.

It is now being considered an alternative source for meeting household energy requirements. WBBSESolutions For Class 10 Chapter 1 Concerns About Our Environment Calorific value of fuel fire ice

Methane hydrate: It is a solid compound of methane. It is mainly found in polar regions under the ice and also under the sea level.

In methane hydrate, the density of methane is very high (about 160 m3 of methane remains in a block of methane hydrate of volume 1 m3).

Methane hydrate can rapidly dissociate with an increase in temperature and a decrease in pressure.

Other names of methane hydrate are methane clathrate, hydro methane, fire ice, etc. The name is ‘fire-ice’ because methane in it starts burning in contact with fire It appears as if ice is catching fire.

Due to the abundance of methane, the compound methane hydrate can be considered a source of energy. Scientists predict, it to be one of the largest sources of energy in the future.

If by adopting effective technology we are able to extract methane hydrate that could change the future energy needs by the replacement of coal, oil, and natural gas.

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2

February 21, 2025June 3, 2023 by vasantha

Model Question Paper Life Science Set 2 Group A

Answer to all questions is compulsory

Write the answer in a complete sentence by choosing the correct answer for each question with the respective serial number.

Question 1. Select the correct pair-

Sclera—Absorbs excess light within the eyeball
Choroid—Provides definite shape of the eyeball
Lens-Causes refraction of light and accomplishes accommodation
Retina-Holds the lens with the help of the suspensory ligaments

Answer: 3. Lens-Causes refraction of light and accomplishes accommodation

Question 2. Identify which of the following statements is not true regarding Adrenaline-

Increases the rate of heartbeat
Helps in the production of spermatozoa during adolescence
Increases cardiac output
Increases systolic blood pressure

Answer: 2. Helps in the production of spermatozoa during adolescence

Question 3. Select which of the following is the feature of tropic movement-

Induced movement of curvature of particular parts of the plant controlled by the direction of the stimulus
It is one type of turgor movement
Induced movement of curvature of particular parts of plant controlled by the intensity of the stimulus
Does not occur under the influence of Auxin

Answer: 1. Induced movement of curvature of particular parts of the plant controlled by the direction of the stimulus

Question 4. Match the words of Column-A with that of Column-B and select which of the following options is correct—
Answer: table-

A-2,B-3,C-1
A-3,B-1,C-2
A-1,B-2,C-3
A-1,B-3,C-2

Answer: 2. A-1,B-3,C-2

WBBSE Class 10 Life Science Model Question Paper 2023

Question 5. Decide which of the following sequence is correct-

Receptor→Effector→Sensory Nerve→Motor Nerve→Nerve Centre
Receptor→Nerve Centre→Motor Nerve→Sensory Nerve→Effector
Receptor→Sensory Nerve→Nerve Centre→Motor Nerve→Effector
Receptor→Motor Nerve→Effector→Sensory Nerve→Nerve Centre

Answer: 3. Receptor→Sensory Nerve→Nerve Centre→Motor Nerve→Effector

Question 6. Select the correct pair-

Telophase- Movement of daughter chromosomes towards poles
Telophase- Disappearance of Nuclear Membrane and Nucleolus
Telophase- Formation of spindle fibre
Telophase- Reappearance of Nuclear Membrane and Nucleolus

Answer: 4. Telophase- Reappearance of Nuclear Membrane and Nucleolus

Question 7. The name of the terminal parts of the Chromosome is—

Centromere
Telomere
Nucleolar Organizer
Satellite

Answer: Telomere

Question 8. Identify which of the following statements is not true regarding cross-pollination-

Requires agent
Origin of new hereditary features
Maintains the purity of species
The rate of germination of seeds is higher

Answer: 3. Maintains the purity of species

Question 9. Consider the differences between asexual and sexual reproduction and select which of the options is/are correct-
Answer:

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2

Answer: Correct option is not provided

Question 10. Select the correct pair in the case of humans:

The normal pattern of the chromosome of ovum — 22A + XX
The normal pattern of the chromosome of the ovum — 22A + Y
The normal pattern of the chromosome of ovum — 22A + X
The normal pattern of the chromosome of ovum — 22A + XY

Answer: 3. Normal pattern of the chromosome of ovum — 22A + X

WBBSE Class 10 Life Science Model Question Paper 2023

Question 11. 1.11Determine which of the following genotypes is homozygous for both the loci

BbRr
BBRr
BbRR
bbrr

Answer: 4. bbrr

Question 12. Identify the genotype of guineapig having white coat colour and rough hair-

bbRR,brr
BBRR,brr
bb,bb
BbRr, BbRR

Answer: 3. bbRR, bbRr

Question 13. Decide which of the following two were selected by Mendel as dominant traits—

Length of stem — Long, Shape of seed — Round
Position of flower — Terminal, the colour of flower — White
Colour of the cotyledon — Green, and Shape of the seed – Wrinkled
Length of stem — Dwarf, Shape of seed – Wrinkled

Answer: 1. Length of stem — Long, Shape of seed — Round

Question 14. Determine the nature of the pea plant germinated from the seed produced as a result of pollination between a hybrid tall (Tt) and a pure dwarf (tt) pea plant—

100% Tall
50% Tall, 50% Dwarf
100% Dwarf
75% Tall, 25% Dwarf

Answer: 2. 50% Tall, 50% Dwarf

Question 15. Decide which of the following diseases can be prevented by taking suggestions from pre-marital genetic counselling-

Goitre
Malaria
Thalassaemia
Tuberculosis

Answer: 3. Thalassaemia

Model Question Paper Life Science Set 2 Group B

2. Answer 21 questions out of 26 questions given below as instructed. Fill in the blanks with proper words in the following sentences (any five):

Question 1. The hormone is found in very high amounts in the ripe seeds of plants.
Answer: Gibberellin

Question 2. Reflex action is fast, spontaneous and
Answer: Involuntary

Question 3. In cell division spindle fibres are not formed.
Answer: amitosis

Question 4. is an entomophilous flower.
Answer: Sunflower

WBBSE Class 10 Life Science Model Question Paper 2023

Question 5. The gene having the power of the rolling tongue is.
Answer: dominant

Question 6. As the gene responsible for hemophilia is recessive, the symptoms of this disease are only manifested in
condition.
Answer: X-linked inheritance

Decide whether the following statements are true or false (any five):

Question 7. The focal length of the lens increases in case of seeing distant objects.
Answer: True

Question 8. Each nucleoside contains a nitrogenous base and phosphoric acid.
Answer: False

Question 9. There is no role of females in determining the sex of humans.
Answer: True

Question 10. If any pea plant contains either TT or tt trait, then the pea plant becomes heterozygous with respect to such alleles.
Answer: False

Question 11. As the flowers of the pea plant are unisexual, so self-pollination and if needed, cross-pollination can be performed.
Answer: True

Question 12. The daughter cells are changed and modified in different ways during cell differentiation phase to form tissue, organ and system.
Answer: True

WBBSE Class 10 Life Science Model Question Paper 2023

Match the words in Column-A with those which are most appropriate in Column-8 and re-write the correct pair mentioning the serial no. of both columns (any five) :

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2 table
Answer: 2.13 – (2), 2.14- (3) 2.15- (4), 2.16- (5), 2.17- (6), 2.18- (1)

Answer in a single word or in a single sentence (any six):

Question 19. Choose the odd one and write it: Olfactory nerve, Vagus nerve, Optic nerve, Auditory nerve
Answer: Vagus nerve

Question 20. What is the fate of hormones in the animal body after its function is over ?
Answer: Hormones are destroyed and excreted immediately after their functions are over.

Question 21. A pair of related terms is given below. On the basis of the relationship in the first pair write the suitable word in the I gap of the second pair. Purine : Adenine :: Pyrimidine :
Answer: Cytosine

Question 22. What happens if the functions of checkpoints in the cell cycle get hampered?
Answer: Genomic instability and/or tumorigenesis

Question 23. What is hybridization?
Answer: Process of interbreeding individuals from genetically distinct populations to produce hybrids.

Question 24. What is a dominant trait?
Answer: A trait produced by a dominant allele in individuals who have one copy of the allele which can come from just one parent.

Class 10 Life Science Model Question Paper With Answers

Question 25. Among the following four terms, one includes the other three. Find it out and write it :
Increase in Basal Metabolic Rate, Thyroxine, Gradual maturation of Red Blood Corpuscle, Exophthalmic Goitre.
Answer: Exophthalmic Goitre

Question 26. In which phase of Interphase are the proteins essential for the formation of spindle fibres in synthesized?
Answer: G2 – phase.

Extensor muscle:

to increase the angle between two body parts.

Abductor’s muscle:

to move limbs away from the midline.

Rotator muscle:

To move limbs around their long axis.

Question 27. Prepare a list of functions controlled by Auxin related to the growth of plants.
Answer:

Major Plant Hormones Auxin

Auxins are a class of nitrogenous phytohormones & the most important growth regulators produced from the growing regions of plant tissue including roots, shoots, and leaves.

These promote cell division, stem and root growth. These can also drastically affect plant orientation by promoting cell division on one side of the plant in response to sunlight & gravity.

The term auxin was first used by Frits Went.

Chemical composition:

Auxins generally occur as complexes, usually found with an amino acid or sugar. These are composed of carbon, hydrogen, oxygen, and nitrogen.

The amino acid Tryptophan and many other Indole compounds serve as precursors of auxins.

Class 10 Life Science Model Question Paper With Answers

Chemical composition:

Auxins generally occur as complexes, usually found with an amino acid or sugar. These are composed of carbon, hydrogen, oxygen, and nitrogen.

The amino acid Tryptophan and many other Indole compounds serve as precursors of auxins.

Types: They are classified into two types as detailed below:

Natural Auxin:

They are Indole compounds like Indole 3-Acetic Acid (IAA) and Non-Indole compounds like Naphthalene Acetic Acid. Indole 3-Acetic Acid was the first plant hormone identified.

It is manufactured primarily in the shoot tips (in leaf primordia and young leaves), in embryos, and in parts of developing flowers and seeds.

Synthetic Auxin:

These are synthetic compounds similar to natural auxin and they include 2,4-D (2,4-Dichlorophenoxy Acetic Acid) or 2, 4, 5-T (2,4,5- Trichlorophenoxy Acetic Acid).

Translocation:

The transport of IAA from cell to cell through the parenchyma surrounding the vascular tissues requires the expenditure of ATP energy.

IAA moves in one direction only i.e., the movement is polar and in this case, downward.

Such downward movement in shoots is said to be basipetal (apex to base) and in roots it is acropetal (outwards towards the root apices from the base).

Synthetic auxins move in all directions inside plants.

Function:

Apical Growth:

Auxins bring about apical dominance and thereby induce apical growth of the shoot.

Tropic movements:

These are deposited unequally on the shoot or root surface and thus cause phototropic curvature and geotropism

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic B Response And Chemical Coordination In Plants Hormones Phototropic curvature and geotropism

Cell enlargement:

Auxin helps to increase the size and volume of the cells.

Cell enlargement is caused by the solubilization of carbohydrates, loosening of wall microfibrils, synthesis of more wall materials, increased membrane permeability, and respiration.

Metabolism:

Auxin stimulates respiration by increasing the availability of respiratory substrate. Thus it enhances metabolism by mobilizing plant resources.

Cambial activity:

The degree of cambial activity is directly proportional to auxin concentration. Auxin also controls xylem differentiation.

Cell division:

It initiates the cell division of the parenchymatous cells at the site of wounded tissue causing healing of wounds after mechanical injury in plants.

Class 10 Life Science Model Paper WBBSE 2023 Set 2

Root formation:

Auxin promotes root initiation at a concentration that is inhibitory for the growth of intact roots.

Parthenocarpic fruit Development:

Pollen contains a lot of auxin, it acts as a signal indicating the completion of pollination and transformation of the ovary to fruit.

Thus the application of synthetic auxin induces the development of fruit without the act of fertilization i.e. parthenocarpic fruit development.

Synthetic auxin (2,4-D) initiates rootings in stem cuttings.

(x)Synthetic auxin can act as a weedicide by killing dicotyledonous weeds preventing the division of cambial tissue.

As monocotyledonous plants are devoid of cambium, they are not destroyed by auxin compounds.

Anti-auxin:

Auxins have an inhibitory effect on the abscission of leaves and fruits, i.e., shedding of mature leaves and ripe fruits from the plant.

It has been found that the abscission zone does not form when the concentration of auxins is high in the leaves or fruits.

On the contrary, Abscisic acid (ABA) is a major hormone in plants that induces the formation of an abscission zone in the leaf stalk or petiole and brings about the shedding of leaves.

It acts as an antiauxin because it counteracts the auxin activity by initiating abscission.

In Plants Hormones Gibberellin

Gibberellins are one of the longest-known classes of non-nitrogenous phytohormones that regulate various developmental processes including stem elongation, germination, dormancy, flowering, and leaf and fruit senescence.

Gibberellic acid or gas can be of more than 100 types and the most common being 3- Gibberellic Acid (GA₃).

Gibberellin was discovered by Kurosawa (1926) from rice plants suffering from Bakanae (foolish seedling) disease caused by Gibberella.

Gibberellins are naturally synthesized in maturing seeds, germinating seedlings, growing tissues of expanding cotyledons, growing leaves, apical buds, root tips, etc.

Class 10 Life Science Model Paper WBBSE 2023 Set 2

Chemical composition:

Gibberellins are tetracyclic diterpene acids. These consist of carbon, hydrogen, and oxygen.
Acetate is the precursor for the synthesis of all kinds of gibberellins.

The gibberellins are named GAj through GAn in the order of discovery.

Translocation:

All known gibberellins are synthesized in plastids and then modified in endoplasmic reticulum and cytosol until they reach their biologically active form.

The transport of gibberellin is not polar. These are transported in all directions from the site of formation through the xylem, phloem, or by cell tq cell.

Functions:

Elongation of internode:

It brings about the growth of the internode and thereby brings about apical growth along with auxin.

Flowering:

It modifies the apical bud to the floral bud, by bringing about the development of floral tissue through modification of the apical meristem.

Breaks seed dormancy:

It breaks seed dormancy and induces germination of seed through denovo synthesis of a-amylase.

Leaf growth:

It helps in the development of young leaves through stimulation of the leaf meristem

It promotes fruit growth and development. It also influences parthenocarpy.

Question 28. Distinguish between the mitosis of plant cells with the mitosis of animal cells on the basis of the following features—

Formation of spindle fibers
Process of cytokinesis

Answer:

Basic Differences Between Mitosis Of Animal Cell And Plant Cell

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Animal cell and plant cell

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle diagrammatic representation of mitosis of a plant cell

Model Question Paper Life Science Set 2 Group C

3. Answer any 12 questions in 2-3 sentences out of 17 questions given below:

Question 1. Prepare a list of hormones that control the following functions—

Causes an increase in the length of bones through mineralization of the matrix of cartilage located at the terminal parts of long bones.

Answer: GH or STH

Transforms ruptured follicle into a temporary endocrine gland namely Corpus Luteum and provides necessary stimulation for the secretion of Progesterone hormone from that gland.

Answer: LH

Inhibits the production of glucose in the liver from protein and lipids.
Answer: Insulin

Causes contraction of uterine muscles during parturition
Answer: Relaxin

Class 10 Life Science Model Paper WBBSE 2023 Set 2

Question 2. Explain the causes of Myopia and Hyperopia
Answer:

Endocrine disorders or hormonal disorders are typically an endocrine disease that results when a gland produces too much (hyper-secretion) or too little (hypo-secretion) of an endocrine hormone, called a hormone imbalance.

Some important hormonal disorders of humans are—

Dwarfism:

Pituitary dwarfism is decreased bodily growth due to hormonal problems (hyposecretion of STH) in childhood.

Causes:

Pituitary dwarfism, or growth hormone deficiency, is a condition in which the pituitary gland does not make enough growth hormone (hypo-function of STH).

Pituitary gland dysfunction can be congenital, which means that the child is born with the abnormality, or can be acquired during or after birth. It tends to run in families.

Symptoms:

The main symptom of pituitary dwarfism is below-average growth, although body proportions will be normal. Other characteristics might include an immature appearance, a chubby body build, a prominent forehead, and an underdeveloped bridge of the nose.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones pituitary and dwarfism

Diabetes insipidus (Dl) is a condition in which the kidneys are unable to prevent the excretion of water due to the hyposecretion of ADH leading to the excretion of an abnormally large amount of urine from the body.

Causes:

During the day, our kidneys filter the blood many times. Normally, most of them are reabsorbed and only a small amount of concentrated urine is excreted.

Dl occurs when the kidneys cannot concentrate the urine normally due to a decrease in the reabsorption of water in the renal tubules and a large amount of dilute urine is excreted.

The amount of water excreted in the urine is controlled by antidiuretic hormone (ADH). Dl caused by a lack of ADH is called central diabetes insipidus.

Excessive thirst that may be intense or uncontrollable, usually with the need to drink large amounts of water.

Excessive urine volume,

Excessive urination, often needing to urinate every hour throughout the day and night.

Goitre:

Goitre is a swelling (hypertrophy) of the thyroid gland in the neck due to hypothyroidism.

Causes:

Iodine deficiency, leading to hypothyroidism, is the major cause of endemic goiter. The thyroid gland needs iodine in order to manufacture thyroid hormones, which regulate the body’s rate of metabolism.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones Diabetes insipidus

Hypothyroidism is the result of an underactive thyroid gland, and this causes goiter. Because the gland produces too little thyroid hormone, it is stimulated to produce more, leading to swelling.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones Hypothyrodism

Symptoms:

The main symptom of goiter is swelling of the thyroid gland, which causes a lump to develop in the front of the neck.

The following are the main symptoms that can result from neck swelling- symptoms of tightness, cough, and hoarseness; Trouble swallowing (dysphagia), dry & rough skin, hair loss, excessive fatigue, etc.

Class 10 Life Science Model Paper WBBSE 2023 Set 2

Diabetes mellitus:

Diabetes mellitus is a chronic, lifelong condition that affects the body’s ability to use the energy found in food.

There are two major types of diabetes:

Type-1 diabetes and
Type-2 diabetes.

Type-1 diabetes is also called insulin-dependent diabetes. It used to be called juvenile-onset diabetes because it often begins in childhood.

Type-2 diabetes used to be called adult-onset diabetes, but with the epidemic of obese and overweight kids, more teenagers are now developing type-2 diabetes.

Type-2 diabetes is also called non-insulin-dependent diabetes.

Causes:

All types of diabetes mellitus have something in common. Normally, our body breaks down the sugars and carbohydrates we eat into glucose.

Glucose fuels the cells in our body. But the cells need insulin, a hormone, in the bloodstream in order to take the glucose and use it for energy.

With diabetes mellitus, either the body doesn’t make enough insulin or it can’t use the insulin it produces or a combination of both.

In Type-2 diabetes, the pancreas usually produces some insulin. But either the amount produced is not enough for the body’s needs, or the body’s cells are resistant to it.

Symptoms:

Since the cells cannot take in the glucose, it builds up in the blood. High levels of FuncIaivientaIs of UFe Sconce
blood glucose can damage the tiny blood vessels in the kidneys, heart, eyes, or nervous system.

That is why diabetes – especially if left untreated – can eventually cause heart disease, stroke, kidney disease, blindness, and damage to nerves in the feet.

The early symptoms of untreated diabetes are related to elevated blood sugar levels and loss of glucose in the urine. The high amount of glucose in the urine can cause increased urine output and leads to dehydration.

This condition is called Polyuria. Dehydration causes increased thirst and water consumption. This condition is known as polydipsia.

The inability of insulin to perform normally has effects on protein, fat, and carbohydrate metabolism. A relative or absolute insulin deficiency eventually leads to weight loss despite an increase in appetite.

This condition is called polyphagia. Some untreated diabetes patients also complain of fatigue, nausea, and vomiting. Fluctuations in blood glucose levels can lead to blurred vision.

Extremely elevated glucose levels can lead to lethargy and coma.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones MAin Symtomps of Diabetes

The Common Hormonal Disorders Are Summarised In The Following Table:

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones hormonal disorder

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals hormone Hormonal disorder

Question 3. Explain what phenomena happen when the following muscles contract :

Flexor muscle :
Extensor muscle :
Abductor’s muscle :
Rotator muscle :

Answer:

Flexor muscle :

To decrease the angle between two body parts.

Extensor muscle :

To increase the angle between two body parts.

Abductor’s muscle :

To move limbs away from the midline.

Rotator muscle :

To move limbs around their long axis.

WBBSE Life Science Class 10 Question Paper Set 2

Question 4. Prepare a list of functions controlled by Auxin related to the growth of plants.
Answer:

Major Plant Hormones Auxin

Auxins are a class of nitrogenous phytohormones & the most important growth regulators produced from the growing regions of plant tissue including roots, shoots, and leaves.

These promote cell division, stem and root growth. These can also drastically affect plant orientation by promoting cell division on one side of the plant in response to sunlight & gravity.

The term auxin was first used by Frits Went.

Chemical composition:

Auxins generally occur as complexes, usually found with an amino acid or sugar. These are composed of carbon, hydrogen, oxygen, and nitrogen.

The amino acid Tryptophan and many other Indole compounds serve as precursors of auxins.

Chemical composition:

Auxins generally occur as complexes, usually found with an amino acid or sugar. These are composed of carbon, hydrogen, oxygen, and nitrogen.

The amino acid Tryptophan and many other Indole compounds serve as precursors of auxins.

Types: They are classified into two types as detailed below:

Natural Auxin:

They are Indole compounds like Indole 3-Acetic Acid (IAA) and Non-Indole compounds like Naphthalene Acetic Acid. Indole 3-Acetic Acid was the first plant hormone identified.

It is manufactured primarily in the shoot tips (in leaf primordia and young leaves), in embryos, and in parts of developing flowers and seeds.

Synthetic Auxin:

These are synthetic compounds similar to natural auxin and they include 2,4-D (2,4-Dichlorophenoxy Acetic Acid) or 2, 4, 5-T (2,4,5- Trichlorophenoxy Acetic Acid).

Translocation:

The transport of IAA from cell to cell through the parenchyma surrounding the vascular tissues requires the expenditure of ATP energy.

IAA moves in one direction only i.e., the movement is polar and in this case, downward.

Such downward movement in shoots is said to be basipetal (apex to base) and in roots it is acropetal (outwards towards the root apices from the base).

Synthetic auxins move in all directions inside plants.

Function:

Apical Growth:

Auxins bring about apical dominance and thereby induce apical growth of the shoot.

Tropic movements:

These are deposited unequally on the shoot or root surface and thus cause phototropic curvature and geotropism

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic B Response And Chemical Coordination In Plants Hormones Phototropic curvature and geotropism

Cell enlargement:

Auxin helps to increase the size and volume of the cells.

Cell enlargement is caused by the solubilization of carbohydrates, loosening of wall microfibrils, synthesis of more wall materials, increased membrane permeability, and respiration.

Metabolism:

Auxin stimulates respiration by increasing the availability of respiratory substrate. Thus it enhances metabolism by mobilizing plant resources.

Cambial activity:

The degree of cambial activity is directly proportional to auxin concentration. Auxin also controls xylem differentiation.

Cell division:

It initiates the cell division of the parenchymatous cells at the site of wounded tissue causing healing of wounds after mechanical injury in plants.

Root formation:

Auxin promotes root initiation at a concentration that is inhibitory for the growth of intact roots.

Parthenocarpic fruit Development:

Pollen contains a lot of auxin, it acts as a signal indicating the completion of pollination and transformation of the ovary to fruit.

Thus the application of synthetic auxin induces the development of fruit without the act of fertilization i.e. parthenocarpic fruit development.

Synthetic auxin (2,4-D) initiates rootings in stem cuttings.

(x)Synthetic auxin can act as a weedicide by killing dicotyledonous weeds preventing the division of cambial tissue.

As monocotyledonous plants are devoid of cambium, they are not destroyed by auxin compounds.

Anti-auxin:

Auxins have an inhibitory effect on the abscission of leaves and fruits, i.e., shedding of mature leaves and ripe fruits from the plant.

It has been found that the abscission zone does not form when the concentration of auxins is high in the leaves or fruits.

On the contrary, Abscisic acid (ABA) is a major hormone in plants that induces the formation of an abscission zone in the leaf stalk or petiole and brings about the shedding of leaves.

It acts as an antiauxin because it counteracts the auxin activity by initiating abscission.

WBBSE Life Science Class 10 Question Paper Set 2

Question 5. Distinguish between the mitosis of plant cells with the mitosis of the animal cell on the basis of the following features—

Formation of spindle fibers
Process of cytokinesis

Answer:

Basic Differences Between Mitosis Of Animal Cell And Plant Cell

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Animal cell and plant cell

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle diagrammatic representation of mitosis of a plant cell

Question 6. Explain how Bryophyllum undergoes vegetative propagation with the help of an adventitious bud.
Answer:

Vegetative Reproduction

Vegetative reproduction is basically a special type of asexual reproduction where a vegetative part of the plant body, separated from the original plant body, develops and grows into a new plant by simple cell division.

The Vegetative Reproduction Is Of Two Kinds:

Methods of natural vegetative reproduction and
Methods of artificial vegetative reproduction.

It occurs naturally through budding, fission, fragmentation, etc. Artificially this reproduction can be carried out by cutting, grafting, etc.

Parthenogenesis or parthenocarpy

Parthenogenesis is a form of asexual reproduction in which the growth and development of the embryo occur without fertilization.

In animals, parthenogenesis means the development of an embryo from an unfertilized egg cell. It is common in rotifers, aphids, bees, and crustaceans.

Some vertebrates like lizards also reproduce by parthenogenesis. Parthenogenesis may be natural or artificial.

Natural parthenogenesis occurs regularly in the life cycle of some animals. It is of two types:

Complete and incomplete parthenogenesis.

Complete parthenogenesis:

It is also called obligatory partheno-genesis.

In this case, the males are completely absent and the females develop from the unfertilized eggs as is found in aphids, phyllopods, and rotifers.

It is also found in some vertebrates.

A lizard Lacerta Mexico Americana reproduces exclusively by parthenogenesis with no males, in the population.

Incomplete parthenogenesis:

In this case sexual generation alternates with parthenogenesis generation.

For example, in bees and wasps, some eggs develop without fertilization and produce males, while those eggs that are fertilized develop into females.

In Gall fly, the larvae may lay eggs which develop parthenogenetically into a new generation of larvae. This is called paedogenetic parthenogenesis or paedogenesis.

In many sexually reproducing animals, the egg can be activated by artificial methods to start the development without fertilization.

This is called artificial parthenogenesis. Eggs of Sea urchins can be made to develop successfully if treated with weak salt solutions, weak organic acids, electric shock or shaking in seawater, or by pricking the egg with a glass needle.

In higher plants, the process of formation of fruits without pollination and fertilization is called parthenocarpy. Parthenocarpy is a form of asexual reproduction seen in flowering plants.

The fruits are generally seedless. During cultivation, parthenocarpy is introduced along with other plant hormones including gibberellin and it results in maturing of the ovaries without the process of fertilization and produces bigger and pulpy fruits.

Pineapples, bananas, cucumber, grapes, watermelon, oranges, pears,s, etc are some examples of parthenocarpy. In some plants, pollination or another stimulation is required for parthenocarpy. This is termed stimulative parthenocarpy.

Plants that do not require pollination or other stimulation to produce parthenocarpic fruits have vegetative parthenocarpy.

Seedless cucumbers are an example of vegetative parthenocarpy and seedful watermelon is an example of stimulative parthenocarpy.

WBBSE Life Science Class 10 Question Paper Set 2

Question 7. Tabulate which changes occur in a chromosome during the Anaphase of Karyokinesis.
Answer:

Changes occur in a chromosome during the Anaphase of Karyokinesis

1. Splitting into daughter chromosomes.
2. Poleward anaphase movement of daughter chromosomes.
3. V, L, or I shaped the appearance of daughter chromosomes.

Question 8. Describe how Yeast completes the process of budding.
Answer:

Yeast completes the process of budding

The asexual reproduction of yeast occurs by budding.

The parent nucleus divides into two daughter nuclei by mitosis.

During budding, the daughter cell first appears as an outgrowth since one daughter nucleus migrates to a corner of the parent cell. Both haploid and diploid cells can undergo budding. The outgrowth enlarges, matures, and detaches from the parent cell.

Question 9. Prepare a list of changes that occur during the adolescence phase of human development
Answer:

Changes that occur during the adolescence phase of human development

The rate of growth becomes rapid.
Secondary sexual characters develop.
Significant growth of sexual organs takes place.
The thought process becomes logical and complex.

Question 10. Explain the following two significances of meiotic cell division—
Maintains the constant number of chromosomes in a species Origin of variation in an organism
Answer:

Significance Of Meiosis

1. Gametogenesis:

It is a necessary part of the life cycle of sexually reproducing animals since it leads to the formation of gametes (sex cells) through meiosis.

2. Maintenance Of Constant Chromosome Number Of A Species:

The gametes produced as a result of meiosis are haploid (n) and the zygote formed by their fusion is diploid (2n).

Thus, it is the only means for restoring the constancy in chromosome number, which is a characteristic of the species from generation to generation.

3. Production Of Variation In Organisms:

Meiosis results in new combinations of genetic material. During crossing over, the hereditary factors from male and female parents get mixed due to the breakage and exchange of chromatids.

This brings in genetic variation within the species. The variations are important raw materials for evolution and also help in the improvement of races.

4. Alternation of generation:

Meiosis causes conversion from sporophytic generation to gametophytic generation in plants, i.e. causes the alternation of generation through prezygotic, post-zygotic, or sporadic meiosis.

Meiosis occurs in sporogenous cells (micro and megaspore mother cells) of the sporophyte-producing haploid spores. The spores on germination form gametophytes (male and female).

Cells of the gametophyte form gametes. Fusion of these gametes again leads to diploid or sporophytic generation and in this way, the alternation of generation between gametophytic and sporophytic generations keeps on going.

Question 11. State Mendel’s second law of heredity.
Answer:

Mendel’s Fourth Postulate

The above analysis became the basis of Mendel’s second general principle or the fourth postulate, the law of independent assortment.

Independent Assortment:

During gamete formation, segregating pairs of unit factors assort independently of each other and undergo random recombination in all possible combinations governed by chance alone.

This postulate stipulates that any pair of unit factors segregate independently of all other unit factors. Thus, according to the postulate of independent assortment, all possible combinations of gametes will be formed in equal frequency.

Question 12. Prove the authenticity of the statement- “The phenotypic and genotypic ratio remain identical in case of Incomplete Dominance”.
Answer:

Incomplete Dominance

A common example of deviation from Mendelism is the phenomenon called incomplete dominance.

A cross between parents with contrasting traits may sometimes generate offspring with an intermediate phenotype.

In a heterozygote organism carrying both a dominant and a recessive allele of the same gene, when the dominant gene cannot express its dominant phenotype completely, a mixed or intermediate, or blended phenotype between the dominant and the recessive is expressed.

Such a situation is known as incomplete dominance. In many plant species, flower color serves as a striking example of incomplete dominance.

With the flowers of Four O’Clocks or floret clusters of Snapdragons Mirabilis jalapeno, a cross between pure breeding red flowered parents and pure breeding white yields hybrids with pink blossoms.

During gametogenesis, the pure red flowered parent plant (AA) produces (A) gametes and the pure white flowered parent plant (aa) produces (a) gametes.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity incomplete dominace

After cross-pollination of parental plants, (A) and (a) unite together to form (Aa) zygote that develops into plants with pink flowers.

Here both the allelomorphic genes have a partial or incomplete dominant relationship and hence, F₁ hybrids show a mixture of characters of both parents. This is a case of incomplete dominance.

If allowed to self-pollinate, the F₁ pink blooming plants produce F₂ progeny bearing red, pink, and white flowers in a ratio of 1: 2 :1. This is the familiar genotypic ratio of an ordinary single gene F₁ self-cross.

What is new is that because the heterozygotes look unlike either homozygote, the phenotypic ratios are an exact reflection of the genotypic ratios.

F₂ Phenotypic ratio = 1 (Red): 2 (Pink): 1 (White) F₂ Genotypic ratio = 1 (AA): 2 (Aa): 1 (aa) In this example of Mirabilis jalapa, the red gene is incompletely dominant over the white gene and so both of them give rise to an intermediate pink colored flower in heterozygous or hybrid condition.

WBBSE Life Science Class 10 Question Paper Set 2

Explanation:

The biochemical explanation for this type of incomplete dominance is that each allele of the gene under analysis specifies an alternative form of a protein molecule with an enzymatic role in pigment production.

If the ‘white’ allele does not give rise to the functional enzyme, no pigment appears.

Thus, in Snapdragons and four o’clock, two ‘red’ alleles per cell produce a double dose of a red-producing enzyme, which generates enough pigment to make the flowers look fully red.

In the heterozygote, one copy of the ‘red’ allele per cell results in only enough pigment to make the flowers look pink. In the homozygote for the ‘white’ allele, where there is no functional enzyme and thus no red pigment, the flowers appear white.

Question 13. Write two causes behind Mendel’s success in conducting experiments on heredity.
Answer:

Reasons for Mendel’s Success

Mendel’s success was dependent upon the following factors:

First, he chose the garden pea (Pisum sativum) as his experimental organism.

These plants can easily be cultivated, crossed, and for each successive generation, Mendel could thus obtain large members of individuals within a relatively short growing season.

By comparison, if he had worked with sheep, each mating would have generated only a few offspring and the time between generations would have been several years.

Second, Mendel examined the inheritance of clearcut contrasting forms of particular traits — round versus wrinkled seed, yellow versus green pod color, etc.

Using such ‘either-or’ traits, he could distinguish and trace unambiguously the transmission of one or the other observed characteristics, because there were neither any intermediate forms nor any of these characters located on separate chromosomes.

Third, Mendel isolated and perpetuated lines of peas that breed true. Mating with such pure breeding lines produce offsprings carrying specific parental traits that remain constant from generation to generation.

Fourth, Mendel carefully controlled his matings, going to great lengths to ensure that the progeny he observed really resulted from the specific fertilization he intended.

Thus he painstakingly prevented the intrusion of any foreign pollen and assured self or cross-pollination as the experiment demanded.

He also performed reciprocal crosses, in which by reversing the traits of male and female parents, he efficiently controlled the path of transmission of a particular trait either via the egg cell within the ovule or via the pollen as per experimental demand.

Fifthly, Mendel worked with a large number of plants, counted and subjected his findings to statistical analysis, and then compared his results with predictions based on mathematical models.

Finally, Mendel was a brilliant practical experimentalist. He could call and observe an optimum number of individuals from the limited space of the monastery garden.

In short, Mendel purposely set up a simplified ‘black and white’ experimental system and then successfully out how it worked.

Genetic Crosses With Guineapig

Mendel worked on pea plants but the application of his laws on animals was carried out by his successors.

Question 14. “Dispersal of animals is one of the driving forces of locomotion”— Judge the statement with the help of proper examples.
Answer:

Reasons And Motivations Behind Locomotion

Animals move for a variety of reasons, such as to find food, a mate, a suitable microhabitat, or to escape from predators.

Hunt For Food & Water:

Since animals can not prepare food, they are to perform locomotion to find out suitable area with plenty of food & water.

To seek shelter & escape from predators:

Locomotion increases the chances of survival of an organism by allowing the organism to seek shelter in favorable habitat, and to escape dangerous situations by avoiding predators.

Dispersal for mating or breeding:

Locomotion enables members of the species to disperse to find suitable mates to coordinate breeding activity and the survival of the young.

Search for a new & favorable environment:

Animals, especially birds, migrate from areas of low or decreasing resources to areas of high or increasing resources. The two primary resources being sought are food and nesting locations. Escaping from cold is also a factor.

Basic differences between movement and locomotion:

Though, in the case of animals, we often use the terms movement and locomotion, interchangeably, there are definite differences between the two.

Locomotion takes place at the organism level while movement can take place at any biological level from cellular to organisms.

In simple words, locomotion is movement from one place to another and involves shifting of the entire body parts (e.g. a person moving or running) and movement involves a change in shape, size, or direction of various body parts (e.g. shaking of your hands).

All kinds of locomotion are movements but all kinds of movements are not locomotion.

Movement is the motion that occurs in an organism or a body with or without the involvement of any change in the position or location of the organism or the body,

while locomotion is defined as the voluntary movement of an organism from one place to another either in search of food or shelter or mate or to escape from the predators.

Therefore, the differences between movement and locomotion may be summarized in a tabular form as below:

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic E Locomotion As A Type Of Response In Animals Movement And locomotion

Question 15. Show the chemical constituents of chromosomes with the help of a table.
Answer:

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2 chromosome

Question 16. Compare DNA and RNA on the basis of the following features

Nature of carbohydrates
Nature of pyrimidine base

Answer:

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle DNA And RNA

Question 17. “Some phenotypes may have multiple genotypes and some other phenotypes may have a single genotype” justify the statement from the results derived from the dihybrid experiment in the case of the pea plant.
Answer:

Mendel’s Experiment And Laws For Dihybrid Cross

As a natural extension of the monohybrid cross, Mendel also designed experiments in which he examined two characters simultaneously. Such a cross, involving two pairs of contrasting traits, is called a dihybrid cross.

Experiment and Observation

Mendel-crossed pea plants that are heterozygous for two genes at the same time.

To construct such a dihybrid, he mated true-breeding plants grown from yellow round peas (YYRR) with true-breeding plants grown from green wrinkled peas (year).

From this cross, he obtained a dihybrid F₁ generation (YyRr) showing only the two dominant phenotypes, yellow and round. He then allowed these F₁ dihybrids to self-fertilize to produce the F₂generation.

When Mendel counted the F₂ generation of one experiment, he found 315 yellow round, 101 yellow wrinkled, 108 round green, and 32 wrinkled green peas. There were, in fact, yellow wrinkled and green round recombinant phenotypes, providing evidence that some shuffling of alleles had taken place.

WBBSE Class 10 Life Science Previous Year Papers

Explanation

From the observed ratios, Mendel inferred the biological mechanism of shuffling the independent assortment of gene pairs during gamete formation.

Because the genes for peas’ color and for shape assort independently, Y can be with R or r in any gamete with equal probability.

Thus, the presence of a particular allele of one gene, say, the dominant Y for pea color, provides no information whatsoever about the alleles of the second gene.

That is, the allele for pea shape in Y carrying game could with equal likelihood be either R or r.

Each dihybrid of the F₁ generation can, therefore, make four kinds of gametes:

YR, Yr, yR, and yr. In a large number of gametes, the four kinds will appear in an almost perfect ratio of 1:1:1:1.

At fertilization then, in a mating of dihybrids, 4 different kinds of eggs can combine with any one of 4 different kinds of pollen, producing a total of 16 possible zygotes in the F₂ generation.

Once again, a Punnett square is a convenient way to visualize the process.

In fact, there are only nine different F₂ genotypes — YYRR, YYRr, YyRr, YyRR, yyRR, yyRr, YYrr, Yyrr, and yyrr — because the source of the alleles (egg or pollen) does not make any difference.

If we look at the combination of the traits determined by nine genotypes, we will see only four phenotypes— yellow round, yellow wrinkled, green round, and green wrinkled — observed in a ratio of 9 : 3 : 3: 1.

If, however, we look at just pea color or just pea shape, we can see that each trait is inherited in the 3: 1 ratio as predicted by Mendel’s law of segregation.

Punnet Square or Checker Board of Dihybrid cross

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Punnet Square or Checker Board of Dihybrid cross

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity f2 generation

Model Question Paper Life Science Set 2 Group D Long Answer Type Questions

4. Write the 6 questions or their alternatives given below. Sightless candidates have to answer a question no. 4.1 A instead of question no 4.1. The marks allotted for each question is 5 (the division of marks is either 3+2, 2+3, or 5) :

Question 1. Draw a scientific diagram of a neuron and label the following parts :

Axon
Node of Ranvier
Dendron
Schwann Cell

Answer:

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic D Response And Physical Coordination In Animals Nervous System neuron

Draw a scientific diagram of the morphological structure of a eukaryotic chromosome and label the following parts—

Chromatid
Telomere
Centromere
Nucleolar Organizer

Answer:

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle metaphase

Write the Functions of the following structural parts of a eukaryotic chromosome :

Centromere
Nucleolar Organizer
Chromatid
Telomere
Kinetochore

Answer:

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle parts of chromosome 2

Question 2. Compare the antagonistic functions of the following three pairs of hormones in the human body:

Insulin and Glucagon
Estrogen and Progesterone
FSH and LH

Explain the relationship between the hindbrain and the function of control of the breathing mechanism.

Antagonistic functions of insulin and glucagon :

1. Insulin increases cellular oxidation of glucose, stimulates the formation and storage of glycogen in the liver & muscles and inhibits the formation of glucose from non-carbohydrates. All these activities result in the maintenance of optimum levels of blood sugar.
Glucagon stimulates liver glycogen to undergo breakdown to be converted to glucose which increases blood sugar levels.

2. Insulin increases protein synthesis in the body. Glucagon hydrolyzes protein into amino acids.

3. Insulin decreases lipid & cholesterol levels in the blood. Glucagon stimulates the increase of fat & cholesterol level in the blood. Antagonistic functions of estrogen and progesterone :

1. Estrogen is secreted by ovaries prior to ovulation. Progesterone is secreted by ovaries after ovulation.

2. During pregnancy, estrogen induces enlargement of breasts and uterus. During pregnancy, progesterone reduces the contractility of the uterus and stimulates the growth of mammary glands.

Antagonistic features of FSH and LH :

1. FSH helps in the maturation of immature follicles into mature Graafian follicles. In the presence of FSH, LH ruptures Graafian follicles causing ovulation.

2. FSH stimulates the secretion of estrogen from Graafian follicles. LH stimulates the secretion of progesterone from the corpus luteum.

3. In males, FSH induces the development of seminiferous tubules and spermatogenesis. In males, LH stimulates the secretion of testosterone in the testis.

The breathing movements (ie., taking in oxygen and taking out carbon dioxide) are initiated in response to the ratio of carbon dioxide and oxygen within the body. High levels of C02 and low levels of 02 collectively influence the body to exhale C02 and take in 02.

This is regulated by the medulla oblongata of the hindbrain. In response to C02 and 02 ratios, medulla oblongata signals the heart and diaphragm accordingly to facilitate respiration.

The respiratory center of the medulla oblongata is concerned with controlling the depth and rate of respiration.

The following physiological functions of a person wounded in an accident are found hampered. Write the name of the parts of the brain attached to those functions :

Speech
Hunger, thirst, and sleep
Posture and the equilibrium of the body
Movement of tongue and swallowing of food

Explain the mechanism of feedback control of the function of hormones with the help of a suitable example.

Speech — Cerebellum
Hunger, thirst, and sleep — Hypotha. lamus
Posture and the equilibrium of the body – Cerebellum

Movement of tongue and swallowing of food – Medulla oblongata

Answer:

Feedback control:

The secretion of most, if not all, hormones is regulated by some type of closed-loop control system known as a feedback mechanism

(because the amount released or secreted is sensed and that information is relayed back to the secretory cell by a variety of ways). Feedback control is mostly negative, rarely positive.

In a negative feedback control, the synthesis of a hormone slows down or halts when its level in the blood rises above the normal or threshold limit.

In the less common positive feedback mechanism, one hormone further stimulates the production of another hormone instead of diminishing it. Some examples of feedback control are given below.

Hypothalamus, in response to some external stimulus, produces a thyrotropin-releasing hormone for the secretion of thyrotropic hormone.

The thyrotropin-releasing hormone (TRH) stimulates the anterior pituitary lobe to secrete thyrotropic hormone. The latter in turn stimulates the thyroid gland to produce thyroxine.

If thyroxine is in excess, it exerts an influence on the hypothalamus and anterior pituitary lobe, which then secrete a lesser amount of releasing hormone and thyroid-stimulating hormone (TSH) respectively.

A rise in the TSH level in the blood may also exert a negative feedback effect on the hypothalamus and retard the secretion of TRH. This restores the normal blood-thyroxine level.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones postively and negatively feedback

Sometimes, the accumulation of a biochemical increases its own production. For example, uterine contraction at the onset of labor stimulates the release of the hormone oxytocin, which intensifies uterine contractions.

The contractions further stimulate the production of oxytocin. This is a positive feedback control.

WBBSE Class 10 Life Science Previous Year Papers

Mode Of Transport Of Animal Hormones:

Most hormones are secreted into the general circulation to exert their effects on appropriate distant target tissues. Water-soluble hormone molecules circulate in watery blood plasma in a free state, (i.e. not attached to other molecules).

Steroid and thyroid hormones are less soluble in aqueous solution and over 90% circulate in blood as complexes bound to specific transport proteins like plasma globulins or albumin.

The transport proteins make the lipid-soluble hormones temporarily water-soluble and act as a ready reserve of hormones.

WBBSE Solutions For Class 10 Life Science Chapter 1 Control And Coordination In Living Organisms Topic C Response And Chemical Coordination In Animals Hormones Thyroid stimulating hormone

Functioning And Fate Of Hormones:

The chemical structure of a hormone enables it to combine with a receptor in the cells of its target. The receptor may be present on the plasma membrane of the cell or inside the cytoplasm or nucleus.

Only a hormone’s “target” cells, which have receptors for that hormone, will respond to its signal. When the hormone binds to its receptor, it forms a receptor-hormone complex.

This complex undergoes changes and enters into the nucleus of the target cell. Within the nucleus, it increases the synthesis of cell protein and takes part in the metabolic process of the cell.

All hormones diminish within the body at differing rates based on their chemical half-life. Once hormones have served their function on their target organs/tissues, these are destroyed.

These are either destroyed by the liver or the tissues of the target organs and excreted out of the body.

Role Of Hormones As Biochemical Messenger And Regulators:

Hormones are informational molecules that carry the message of metabolic change from the endocrine glands to the target cells or organizer

These are released into the extracellular fluid, where they are diffused into the bloodstream. The latter carries them from the site of production to the site of action.

Hormones stimulate or inhibit one or more Physiological processes for the welfare of the body.

Maintenance of the internal chemical environment of the body to a constant is called homeostasis. Hormones play a major role in maintaining homeostasis through their integrated action.

These also play a leading role in the chemical coordination of the living body. Thus hormones are known as chemical messengers.

Question 3. Prepare a list of the role of artificial plant hormones in agriculture and horticulture. What are the influences of Insulin hormone on the absorption and metabolism of glucose in the human body?
Answer:

Pancreas:

The pancreas is a large elongated gland located in the abdominal cavity just inferior and posterior to the stomach.

Hormonal Secretions:

The pancreas is considered to be a heterocrine or mixed gland as it contains both endocrine and exocrine tissue. The endocrine function consists primarily of the secretion of the two major hormones, insulin, and glucagon.

The endocrine cells of the pancreas are found in small groups throughout the pancreas called islets of Langer Within these islets are two major types of cells alpha and beta cells.

The alpha cells produce the hormone glucagon and the beta cells produce the hormone insulin.

Insulin:

It is an antidiabetogenic protein hormone that lowers blood sugar levels.

Functions:

Effect on carbohydrate metabolism:

Insulin increases the oxidation of glucose in the cells, stimulates the formation & storage of glycogen in the liver & muscle, inhibits the formation of glucose from non-carbohydrates in the liver, and increases the permeability of glucose through the cell membrane from blood to the cells.

All these activities result in the maintenance of optimum levels of blood sugar.

Effect on protein metabolism:

It increases protein synthesis in the body.

Effect on fat metabolism:

It also decreases lipid & cholesterol levels in the blood & prevents the formation of harmful ketone bodies in the liver.

Glucagon:

It is anti-insulin in nature. Together with insulin, it maintains a steady level of blood sugar in the body.

Functions:

Effect on carbohydrate metabolism: It stimulates liver glycogen to undergo breakdown to be converted into glucose which increases blood sugar levels.

WBBSE Class 10 Life Science Previous Year Papers

Effect on protein metabolism:

Glucagon hydrolyses protein into amino acids and increases nitrogen excretion through urine.

Effect on fat metabolism:

It stimulates the increase of fat & cholesterol level in the blood.

Gonads:

The gonads and ovaries in females and testes in males are responsible for producing the sex hormones of the body.

Testes:

The testes are a pair of ellipsoid Fun(Iami iniaIs of Lifi Sell no organs found in the scrotum of males that produce the androgen testosterone in males after the start of puberty.

Testosterone:

It has effects on many parts of the body, including the muscles, bones, sex organs (both primary & secondary), and hair follicles,

During puberty, testosterone controls the growth and development of the sex organs and secondary sex characteristics like muscular growth, breaking of voice, growth of hair on the face, chest, etc.

Ovaries:

The ovaries are a pair of almond-shaped glands located in the pelvic body cavity lateral and superior to the uterus in females. The ovaries produce the female sex hormones progesterone and estrogens. It also secretes another hormone called relaxin.

Estrogen:

Oestrogen stimulates the growth, development, and functional activities of primary and secondary sex organs in females during puberty.

It regulates the menstrual cycle and stimulates breast development.

It enhances the deposition of fat in the female body.

Progesterone:

In the presence of estrogen, progesterone stimulates the complete development of the primary & secondary female sex organizer

It is most active during ovulation & pregnancy. It helps the embedding of embryos in the uterus and stimulates the development & maintenance of pregnancy.

It also regulates the menstrual cycle & breast development at puberty.

Relaxin:

It is secreted from the uterus at the terminal stage of pregnancy. It facilitates the expulsion of the fetus from the uterus by causing relaxation of the pelvic ligaments.

Write three differences between binocular vision with that of monocular vision on the following three aspects :

Formation of image
Field of vision
Depth

Write differences between inborn and acquired reflex actions on any two of the following aspects-

Nature
Condition
Prior experience
Neural pathway

Answer:

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2 table 2

Applying the brake of a car at a red signal.
Sweating
opening the door on hearing the doorbell
looking left or right before crossing the road
knee jerk.

Mention the differences between conditioned and unconditioned reflex actions.

Conditioned reflex action
Unconditioned reflex action

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic D Response And Physical Coordination In Animals Nervous Conditioned and unconditioned reflex

Question 4. Show the alternation of generation in fern with the help of a word diagram.
Answer:
WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction Alternation of generation

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction dryoptersis

Show the process of sexual reproduction in flowering plants with the help of a word diagram :
Answer:

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2 mircosphore

Question 5. Distinguish between Mitosis and Meiosis on the basis of the following three aspects-

Site of occurrence
Nature of division of chromosome
Number of cells produced

Explain the following phenomena related to meiotic cell division—

Separation of chromosome and chromatid
Crossing over

Answer:

Important features of meiosis

WBBSE Class 10 Life Science Previous Year Papers

1. Homologous Chromosomes:

These are chromosome pairs of approximately the same length and centromere position. Note that diploid cells have two sets or one pair of homologous chromosomes.

Out of the pair, one is inherited from the mother (maternal) and one from the father (paternal).

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Homologous chromosomes

2. DNA replication:

Replication of DNA takes place during the interphase preceding meiosis. DNA replication generates sister chromatids from each chromosome. Sister chromatids are two identical copies of a chromatid that remain closely aligned.

Although DNA replication occurs in interphase, no longitudinal doubleness of chromosomes is visibly evident in Leptotene of Prophase I owing to contraction.

3. Synopsis:

The movement of chromosomes initiates in the zygotene stage and this movement results from an attracting force that brings the homologous pair of chromosomes together.

The chromosomes become shorter and thicker due to compaction.

When they come closer, homologous chromosomes pair and align at the equatorial plate of the cell for equal qualitative and quantitative distribution. The pairing takes place throughout the length.

This process of pairing is known as synapsis Pairing takes place not only between the homologous chromosomes but also between homologous regions of the chromosomes. Chromosome pairs undergoing synapsis have approximately the same length and centromere position.

Out of the pair, one is inherited from the mother (maternal) and one from the father (paternal). Non-sister chromatids belong to homologs.

WBBSE Class 10 Life Science Model Question Paper 2023

These are chromosome pairs having the same length, staining pattern, centromere position as well as the same characteristics of genes at particular loci.

A homologous pair of chromosomes consists of one chromosome from each parent and they are known as bivalents. Each chromosome of a bivalent is found to have two chromatids. Thus the four chromatids of a bivalent are together known as a tetrad.

4. Crossing Over:

The pachytene subphase of Prophase I is marked by a process called Crossing over that happens after both the homologous chromosomes in a pair join up to form a structure called a tetrad through synapsis.

Once a tetrad is formed, a portion of each homologous chromosome breaks off transversely and is re-attached to the same part of its homolog. Crossing over occurs between non-sister chromatids of homologous Sister Chiasma chromatids chromosomes.

This mixes up the traits that are found in each of the chromosomes, thus resulting in genetic recombination due to the exchange of segments between two non-sister chromatids belonging to a bivalent tetrad.

As a result of crossing over, X like structure is formed between the non-sister chromatids. The point of attachment at the crossing-over is called chiasma. It occurs during Diplotene.

The number of chiasmas may be one, two, or more depending on the length of the chromosomes.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle crossing over

5. Terminalization Of Chiasmata:

Chiasmata are generally pushed to the terminal ends of the chromosomes and this process is known as the terminalization of chiasmata (singular: chiasma).

The pair of homologous chromosomes begin to separate in the diplotene subphase of prophase I and chiasmata are fully terminalized in the diakinesis subphase of prophase.

Reduction in chromosome number:

During metaphase I, the tetrads line up on the plate. During anaphase I, the homologous chromosomes separate from one another i.e. one homologous chromosome with its two sister chromatids move to opposite poles.

Thus each pole has a haploid (n) number of chromosomes i.e. a reduction in chromosome number is achieved at this stage.

Telophase results in the formation of two haploid (n) daughter nuclei with each chromosome having two chromatids. For this reason, the first meiotic division is known as the reductional or heterotypic cell division.

7. Equational division:

Meiosis II or the second meiotic division has four phases similar to mitosis and is the second round of cell divisions during meiosis whereby the cells formed during Meiosis I divide again to form four haploid (n) gametes.

Between these two stages, the interkinesis or interphase is either quite short or skipped, unlike normal mitosis. Because of this, the S phase does not occur and so the DNA in these cells is not copied, making the resulting cells from this phase haploid.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Mother cells

Distinguish between the cytokinesis of plant cells with the cytokinesis of animal cells on the basis of the following aspects :

Process
Time of initiation
Role of Golgi bodies

Answer:

The longest phase of mitosis:
Prophase

The shortest phase of mitosis:
Anaphase

WBBSE Class 10 Life Science Model Question Paper 2023

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Animal cell and plant cell

Establish the interrelationships among genes, DNA, and chromosome.
Answer:

Inter-Relationship Among Chromosome, DNA, And Gene

The eukaryotic cells contain a membrane-bound nucleus which is designated as the ‘Director of the cell’.

The nucleus contains many thread-like, coiled, and elongated structures called chromatin fibers or chromatin reticulum, or nuclear reticulum.

The fibers of chromatin are uniformly distributed in the nucleoplasm. Chromatin fibers are observed only during the interphase or the preparatory phase of the cell cycle.

Just prior to cell division, chromatin fibers condense, become thick, and wrap up very tightly to form ribbon-like structures called chromosomes.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic A Cell Division And Cell Cycle Chromosome

The number of particular species. They are usually found in pairs. Human beings have 23 pairs of chromosomes in each body cell.

The chromosome consists of a proteinaceous matrix and two spirally coiled chromonemata, each one of which contains a single DNA molecule.

The nucleus of an average human cell is only 6m in diameter, yet it contains 1.8 m of DNA which is distributed amongst the 23 pairs or 46 chromosomes each consisting of a single DNA molecule of about 40 mm.

Thus, Chromatin represents long-thin strands of the DNA-protein complex. It is unfolded and uncondensed form of DNA, while chromosomes are condensed DNA and protein.

The function of chromatin is to store DNA in the nucleus. Chromosomes are the bearers of hereditary instructions and regulate cellular processes.

DNA (or deoxyribonucleic acid) is the molecule that carries the genetic information in all cellular forms of life and some viruses.

It belongs to a class of molecules called nucleic acids, which are polynucleotides that is, long chains of nucleotides. Nucleotides are made up of a base, a sugar, and a phosphate. The four bases

chromosomes are constant in the nucleus for adenine (A), guanine (G), cytosine (C), and thymine (T) pair with each other (A with T and G with C).

WBBSE Class 10 Life Science Model Question Paper 2023

It is the order or sequence of these base pairs that provides the information needed for the growth and development of our bodies.

Specific parts of DNA carry the code for producing specific proteins which ultimately lead to the expression of different characters in an organism.

Each of these parts of DNA is termed a gene. Thus gene is the fundamental physical and functional unit of heredity that carries information from one generation to the next.

It is a segment of DNA, composed of a transcribed region and a regulatory sequence, that makes possible transcription. A series of genes are present in each DNA.

The coordinated interaction of two or more genes produces a given phenotypic trait. A complete set of chromosomal genes is inherited by the offspring as a unit from the parent.

Question 6. Predict what would be the hereditary results in the following cases :

One of the parents is thalassaemic and the other is a carrier of the thalassaemic gene.
Both of the parents are carriers of the thalassaemic gene.

What are the symptoms of Thalassaemia?
Answer:

WBBSE Class 10 Life Science Model Question Paper 2023 Set 2 normal carrier

Tabulate three pairs of opposite traits regarding the seed of the pea plant as selected by Mendel. Show the process of sex determination in men with the help of a checkerboard.

Answer:

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity antagonistic pairs

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Genetic sex

WBBSE Class 10 Life Science Model Question Paper 2023 Set 1

February 21, 2025June 3, 2023 by vasantha

Model Question Paper Life Science Set 1 Group A

Answer to all questions is compulsory

1. Write the answer in complete sentences by choosing the correct answer for each question with the respective serial number.

Question 1. Select the correct pair-

Cerebrum-Maintenance of the balance of the body
Hypothalamus-Control of intelligence and emotion
Cerebellum-Control of body temperature
Medulla Oblongata-Control of heartbeat and swallowing of food

Answer: The correct Pair is- Medulla Oblongata—Control of heartbeat and swallowing of food.

Question 2. Identify which of the following statements is not true regarding Insulin-

Helps in the absorption of glucose from the blood into most of the somatic cells
Converts glucose into glycogen within liver and muscle cells
Helps in the conversion of fat and protein into glucose
Inhibits the conversion of protein and fat into glucose

Answer: The statement which is not true regarding Insulin is—Helps in the conversion of fat and protein into glucose.

Question 3. Match the words of Column-A with that of Column-B and select which of the following options is correct-

WBBSE Model Question Paper 2020 Life Science And Environment Set 3 Match The Columns.

1-1, 2-2,3-3
1-2, 2-3, 3-1
1-3, 2-1, 3-2
1-2, 2-1, 3-3

Answer: 3. 1-3, 2-1, 3-2

Question 4 Determine from the answers given below in which phases of karyokinesis during mitotic cell division following two incidents happen- 1. Daughter chromosomes tend to move apart from each other towards their own poles Nuclear membrane and nucleolus disappear

1. Prophase 2. Anaphase
1. Anaphase 2. Prophase
1. Telophase 2. Metaphase
1. Metaphase 2. Telophase

Answer: 2. During mitotic cell division—

Daughter chromosomes tend to move apart from each other towards their own poles— Anaphase and
Nuclear membrane and nucleolus disappear—Prophase

Question 5. Select which of the following is the feature of cross-pollination-

Occurs within the same flower of the same plant
Agents are not required
Lesser chance of new characters being transmitted
More wastage of pollen grains

Answer: The feature of cross-pollination is— More wastage of pollen grains.

WBBSE Class 10 Life Science Model Question Paper 2023

Question 6. Determine the number of DNA molecules that get coiled to form each chromosome in a newly formed daughter cell produced by mitotic cell division in the human body-

46
1
23
Numerous

Answer: 2. The number of DNA molecules that get coiled to form each chromosome in a newly formed daughter cell produced by mitotic cell division in the human body is 1.

Question 7. Identify the genotype of guineapig having black colour and rough hair-

BbRr, BBRr
bbRR, bbRr
BBrr, Bbrr
bbrr, bbRr

Answer: 1. The genotype guineapig having black colour and rough hair are—BbRr, BBRr.

Question 8. Decide which of the following two were selected by Mendel as recessive traits-

Colour of the flower-purple, the position of flower-axial
Length of stem-dwarf, a form of ripe seed-wrinkled
Form of the ripe seed-rund, the colour of seed- yellow
Position of flower-axial, length of stem- tall

Answer: 2. Length of stem—dwarf and Form of ripe seed—wrinkled were two recessive traits selected by Mendel.

Question 9. Asses from the following, the probable genotype of parents having a haemophilic son and normal daughter-

H || h, h
H || H, H
H || H, h
H || h, H

Answer: 3. The probable genotype of parents having a haemophilic son and normal daughter are- H || H, h

Question 10. Parthenium is an exotic species in our country. Other indigenous species cannot survive in such places where it grows. This establishes one of the postulates of Darwin’s theory. Identify the postulate-

Intraspecific struggle
Interspecific struggle
Struggle with environment
Origin of new species

Answer: 2. The correct postulate is Interspecific struggle.

Question 11. Miller and Urey, in their experiment, were able to synthesize some preliminary constituents necessary for the creation of life. Identify the ones which were amino acids among them-

Lactic acid, Acetic acid
Urea, Adenine
Glycine, Alanine
Formic acid, Acetic acid

Answer: The amino acids were—Glycine and Alanine.

WBBSE Class 10 Life Science Model Question Paper 2023

Question 12. Decide for which of the following purposes bees demonstrate waggle dance-

Search for reproductive mates
Inform other worker bees about the direction and the distance of the source of food from the bee hive
Selecting a place for the construction of the new bee hive
Avoid attack by probable enemy

Answer: 2. Bees demonstrate waggle dance to-^ Inform other worker bees about the direction and the distance of the source of food from the bee hive.

Question 13. Identify which of the following is the correct information related to biosphere reserve-

Conservation is promoted to local people and other biotic communities along with the conservation of the ecosystem
National Park and Sanctuary are not included within the biosphere reserve
The presence and participation of local people in the conservation of the ecosystem are not permissible
Its size is usually smaller than a Sanctuary

Answer: 1. The correct information related to biosphere reserve is- conservation is promoted to local people and other biotic communities along with the conservation of the ecosystem.

Question 14. Decide which of the following pair is not correct-

Poaching-Increase the endangeredness of gorilla
Exotic species-Lantana, Tilapia
Determination of hotspot-Number of endemic species and endangered species
Greenhouse gas-Eutrophication

Answer: The wrong pair is—A greenhouse gas— Eutrophication

Question 15. Decide which of the following Project Tiger is located within our state-

Bandipur
Simlipal
Sunderbans
Kanha

Answer: Sunderbans Project Tiger is located within our state.

WBBSE Class 10 Life Science Model Question Paper 2023

Model Question Paper Life Science Set 1 Group B

2. Answer any 21 questions out of the 26 questions given below instructed.

Fill in the blanks with proper words in the following sentences (any five):

Question 1. Acharya Jagadish Chandra Bose proved the property of __________ by sending electrical impulses in Mimosa and Desmodium plants.
Answer: Sensitivity

Question 2. If gametes in humans were produced by mitosis instead of meiosis then the number of autosomes in a somatic cell of an offspring would have been __________.
Answer: 88

Question 3. A disease in the human population caused by a recessive gene located in the ‘X’ Chromosome is __________.
Answer: Haemophilia

Question 4. The hoof of modern horse is the transformation of the digit number __________ of their ancestors.
Answer: 3

Question 5. At the __________ phase of the nitrogen cycle, ammonia is converted into nitrite and nitrate by the action of some bacteria.
Answer: Nitrification

Question 6. To produce the bottled cold drinks widely sold in the market, a lot of __________ water is wasted.
Answer: 2.6 Fresh

Decide whether the following statements are true or false (any five):

Question 7. Tropic movement is the movement of growth in plants.
Answer: True

WBBSE Class 10 Life Science Model Question Paper 2023

Question 8. Crossing over takes place during mitotic cell division.
Answer: False

Question 9. Mendel used the term gene while describing his experiments related with heredity.
Answer: False

Question 10. The leaf of the Cactus is modified into the spine for the reduction of the rate of transpiration.
Answer: True

Question 11. Rhododendron is an endangered plant species conserved in the Eastern Himalaya hotspot.
Answer: True

Question 12. Choroid helps in the accommodation of the eye by changing the curvature and shape of the lens.
Answer: False

Match the words in Column-A with those which are most appropriate in Column-B and re-write the correct pair mentioning the serial no. of both Columns (any five):

WBBSE Model Question Paper 2020 Life Science And Environment Set 3 Match The Columns

Answer: 13. D, 14. G, 15. A, 16. E, 17. B, 18. C

Answer in a single word or in a single sentence (any six):

Question 19. Choose the odd one and write it: Cerebrum, Hypothalamus, Pons, Thalamus
Answer: Pons

Class 10 Life Science Model Paper WBBSE 2023

Question 20. Where the Schwann cells are located?
Answer: Schwann cells are found in close contact with axons in the peripheral nerves.

Question 21. A pair of related terms is given below. On the basis of the relationship in the first pair write the suitable word in the gap of the second pair. Mitosis: Radicle :: Meiosis: __________.
Answer: Spore mother cell

Question 22. Which law did Mendel conclude from his dihybrid cross experiment?
Answer: Law of Independent Assortment

Question 23. Give an example of a variation found among healthy persons which is transmitted through generations.
Answer: Rolling tongue and non-rolling tongue

Question 24. How do Chimpanzees break open the hard shells for eating the nuts?
Answer: Chimpanzees put the nut on the flat surface of a hard stone and use another stone or tough piece of wooden branch as a hammer to break the shell of nut.

Question 25. Among the following four terms, one includes the other three. Find it out and write it: SPM, Air Pollution, Greenhouse gas, Lung disease.
Answer: Air pollution

Question 26. Name the practice which jointly the local peoples and forest department maintain for the reclamation of a forest.
Answer: Joint Forest Management (JFM)

Model Question Paper Life Science Set 1 Group C

3. Answer any 12 questions in 2-3 sentences out of the 17 questions given below.

Question 1. Distinguish between the functions of hormones and the nervous system on the following parameters:

Nature of function
Pace of function
A time span of function
Fate

Answer:

Differences between the endocrine system and nervous system

WBBSE Solutions For Class 10 Life Science And Environment Chapter 1 Response And Physical Co-Ordination In Animals Nervous System Endocrine and nervous system

Question 2. ‘A person can see distant objects distinctly but is unable to visualize near objects in a perfect way’-Predict what would be the probable cause and suggest the corrective measure for such a problem.

Answer:

Defects Of Visions And Corrective Measures

A person with normal eyes can, by virtue of accommodation, see clearly all objects that are at a distance greater than about 25 cm from the eye.

If due to certain abnormalities the eye is unable to accommodate itself to various distances, then the eye is said to be defective.

Some common defects of the eye are—

1. Myopia:

Near-sightedness, also called myopia is the common name for impaired vision in which a person sees near objects clearly while distant objects appear blurred.

In such a defective eye, the image of a distant object is formed in front of the retina and not at the retina itself. Consequently, a nearsighted person cannot focus clearly on an object farther away than the far point of the defective eye.

Class 10 Life Science Model Paper WBBSE 2023

Causes:

This defect arises because the power of the eye is too great due to the decrease in the focal length of the crystalline lens.

This may arise due to either-

Excessive curvature of the cornea, or

Elongation of the eyeball.

Correction:

This defect can be corrected by using a concave (diverging) lens. A concave lens of appropriate minus (-) power or focal length is able to bring the image of the object back to the retina itself.

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic D Response And Physical Coordination In Animals Nervous System conacave convex

2. Hyperopia or hypermetropia:

Far-sightedness, also called hyperopia or hypermetropia, is the common name for a defect in vision in which a person sees near objects with blurred vision, while distant objects appear in sharp focus.

In this case, the image is formed behind the retina.

Causes:

This defect arises because either

the focal length of the eye lens is too great, or

the eyeball becomes too short so that light rays from the nearby object cannot be brought to focus on the retina to give a distinct image.

Correction:

This defect can be corrected by using a convex (converging) lens of appropriate focal length. Eyeglasses with converging lenses supply the additional focusing plus (+) power required for forming the image on the retina.

3. Presbyopia:

Presbyopia is a progressive form of farsightedness that affects most people by their early 40s. The power of accommodation of the eye decreases with aging.

Most people find that the near point gradually recedes.

Causes:

It arises due to the gradual weakening of the ciliary muscles and diminishing flexibility of the crystalline lens.

Correction:

Simple reading eyeglasses with convex lenses correct most cases of presbyopia.

Sometimes, a person may suffer from both myopia and hypermetropia. Such people often require bifocal lenses.

In the bifocal lens, the upper portion of the bifocal lens is a concave lens, used for distant vision. The lower part of the bi-focal lens is a convex lens, used for reading purposes.

Class 10 Life Science Model Paper WBBSE 2023

Cataract:

Generally, this defect can be found in aged or old people. Persons with this defect get blurred vision which sometimes even lead to total blindness.

The reason for this defect is that the lens loses its transparency and become opaque due to the deposition of protein material and calcium mineral in the lens.

This opaque condition of the lens does not allow the light rays from an object to pass through the lens. This defect can be rectified by surgically removing the lens and it has to be replaced by a highly convex lens.

Before intraocular lenses (lOLs) were developed, people had to wear very thick eyeglasses or special contact lenses to be able to see after cataract surgery.

Now, with cataract lens replacement by phacoemulsification or phaco surgery, several types of IOL implants are available to help people enjoy improved vision.

Question 3. Analyze the role of synthetic plant hormones in increasing production and solving the problem of weeds in agriculture.

Answer:

Role of synthetic hormones:

Synthetic hormones are successfully used in agriculture and horticulture. The roles of these synthetic hormones are mentioned below.

1. Developing new plants from stem cuttings:

Cuttings are used for artificial vegetative propagation of different plants like roses, Hibiscus, marigold, Chrysanthemum, ‘etc. After cutting the twigs from a mother plant, a solution of synthetic auxin or auxin powder is applied at the cut end.

Then, these cuttings are planted in moistened soil. By the action of this hormone, adventitious roots grow from the cut end and the cutting grows as an individual daughter plant.

2. Preventing shedding of immature fruits:

Sometimes, immature fruits shed off from the plant if these plants are sprayed with synthetic auxin solution for a few times during ear y developmental phase of the fruits, the rate of immature shedding declines sharply.

Horticulturists spray auxin solution on mango, litchi, grapes, banana, and several other fruit plants to prevent immature shedding of fruits. Synthetic gibberellin and synthetic cytokinin are also effective.

Class 10 Life Science Model Question Paper With Answers

3. Destroying weeds:

Weeds growing in crop fields share water and nutrients with agricultural crops. This affects the quality of production. Scientists have revealed that the application of certain phytohormones destroys dicotyledonous herbs and shrubs.

Application of a synthetic auxin named 2, 4-D effectively kills dicotyledonous weeds from monocot crop (paddy, wheat, etc.) fields.

4. Production of parthenocarpic fruits:

Fruits, produced from the ovary without fertilization do not contain seeds and become larger. These are called parthenocarpic fruits. A treatment of auxin solution before the maturation of flowers triggers the development of the ovary.

As a result, seedless fruits are produced before fertilization. Synthetic auxin is successfully applied on the plants of guava, grapes, banana, watermelon, etc. to produce seedless fruits.

Synthetic gibberellin is comparatively more effective on tomato plants. These two synthetic phytohormones are used to produce parthenocarpic fruits.

Question 4. LH and ICSH control the secretion of hormones of the reproductive glands of the human body’-judge the validity of the statement.

Answer:

In the female body, Lutenising Hormone (LH) stimulates ovule secretion and the formation of corpus luteum from the Graafian follicle. It also helps in the secretion of progesterone hormone from the corpus luteum.

In the male body, Interstitial Cell Stimulating Hormone (ICSH) stimulates the interstitial cells of Leydig of testes to secrete testosterone.

Question 5. How can you distinguish between the mitosis of plant cells and that of animal cells on the basis of the formation of spindle fiber and the process of cytokinesis?

Answer:

Distinguish between the mitosis of plant cells and that of animal cells are-

WBBSE Solutions For Class 10 Life Science And Environment Chapter 2 Mitotic And Meiotic Differences between mitosis in plant cell and animal cell

Question 6. Establish the relationship between the formation of malignant tumors in the human body with the loss of control in the cell cycle.

Answer:

The relationship between the formation of malignant tumors in the human body with the loss of control in the cell cycle

Checkpoints prevent uncontrolled cellular growth and thereby cancer. It mainly checks the genetic as well as physical integrity, if they found any genetic defect, they immediately arrest the cell from going to cellular division.

All cells will be checked in three stages. But if the genes which are responsible for the synthesis of checkpoints are mutated then they lost their control over cell division and the cells are going to divide in an uncontrolled way.

This uncontrolled cellular division gives rise to a cellular lump, called a tumor.

Class 10 Life Science Model Question Paper With Answers

Question 7. ‘The adventitious leaf bud plays a significant role in natural vegetative propagation of plant’-Evaluate the validity of the statement with a proper example.
Answer:

Natural Vegetative Propagation

Different plant parts are variously modified for vegetative propagation.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction Formation of new plant from vegetative plant

Natural vegetative propagation in higher plants:

Root:

The storage root acts as a structure for perpetuation, they help the organism to survive during unfavorable conditions and also germinate to produce a new plant body. e.g. Root tuber of sweet potato, Dahlia.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction root

Stem:

The stem may also act as a parenting organ, which can grow and propagate on land and water and when separated, produces a new plant body. e.g. Offset of Water Hyacinth.

The propagation of stem in terrestrial plants is brought about by runner and stolon, e.g. There are various artificial methods like strawberries and grasses. Rhizomes are cutting, grafting, micropropagation, etc.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction stem

underground horizontally growing stems having nodes, internodes, and axillary buds. Branches grow from these buds.
Tuber is a modified underground stem tip.

The eyes or buds present on the tuber grow into new plants. The bulb is a modified shoot that has short stems and apical & axillary buds that grow to form shoots.

Leaf:

The leaf may become a propagating organ with the presence of storage food in the lamina and adventitious buds present at the edge of the lamina may germinate to produce a new plant body. e.g. Leaf of Bryophyllum.

WBBSE Solutions For Class 10 Life Science Chapter 2 Continuity Of Life Topic 2 Reproduction leaf

Question 8. Show with the help of a cross, who is more important among parents in determining the sex of their offspring.
Answer:

Sex Determination In Human

The term sex refers to sexual phenotype. Most organisms have only two sexual phenotypes—male and female.

We, normally, define the sex of an individual organism in reference to its phenotype. The mechanism by which sex is established is termed sex determination.

Sometimes an individual organism has chromosomes that are normally associated with one sex. For example, the cells of female humans normally have two X chromosomes, and the cells of males have one X chromosome and one Y chromosome.

Class 10 Life Science Model Question Paper With Answers

Sex Determination In Humans:

In humans, Drosophila, and many other species, the cells of males and females have the same number of chromosomes, but the cells of males have a single X chromosome and a smaller sex chromosome, the Y chromosome.

The Y chromosome is not Y shaped as is commonly assumed but is acrocentric. In this type of sex determination system, the male (44A + XY) is heterogametic because half of the male gametes have an X chromosome and the other half have a Y chromosome.

The female (44A + XX) is homogametic because all the eggs contain a single X chromosome. Fertilization of an egg (always X-bearing) with an X-bearing sperm produces female offspring (XX), but a Y-bearing sperm produces male offspring (XY).

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity homozygotes

The Total Chromosomes In Humans, In Each Body Cell, Can Be Represented As-

Female chromosomes – 44+XX where 44 are the autosomes and XX chromosomes are the sex chromosomes.

Male chromosomes – 44+XY where 44 are the autosomes and XY chromosomes are the sex chromosomes.

Although the X and Y chromosomes are not homologous, they pair and segregate into different cells in meiosis.

This is because of the fact that these chromosomes are homologous in small regions, called the pseudoautosomal region, in which they carry the same genes. In both types, the human X and Y chromosomes contain pseudoautosomal regions.

In humans and other placental mammals, maleness is due to a dominant effect of the Y chromosome. This is evidenced by the study of individuals with an abnormal number of sex chromosomes or aneuploidy.

XO persons (Turner syndrome) develop as females and XXY persons (Klinefelter syndrome) develop as males.

The dominant effect of the Y chromosome is exhibited early in development when it directs the primordial gonads to develop into testes.

Once the testes are formed, they secrete the hormone testosterone, which stimulates the development of male secondary sexual characteristics.

It is now known that the testis-determining factor (TDF) is the product of a gene called SRY (Sex-determining region Y), which is located outside the pseudoautosomal region in the short arm of the Y chromosome.

When fertilization occurs, the zygote (the initial cell from which a fetus grows) always inherits one of the mother’s X chromosomes, and either an X or a Y from the father, depending on which chromosome the fertilizing sperm cell happened to inherit.

One could say, then, that the father or, at least, his sperm determines the sex of the child.

The generally accepted theory is that males determine the sex because males can donate either an X chromosome or Y chromosome, while females can only donate an X chromosome to their offspring, making their contribution constant and the male’s contribution.

The variable, which under normal circumstances, determines the offspring’s genetic sex (at least, in humans Moreover, genetically there is a 50% chance of having a boy and a 50% chance of having a girl, as is found out from.

But there are actually slightly more boys born every year than girls.

It’s unclear why this is the case, but some research points out that more female fetuses die during pregnancy than male.

The Y chromosome contains all the directions that make the human zygote develop into a male. It is a relatively small chromosome with about 30 genes.

WBBSE Class 10 Life Science Previous Year Papers

In comparison, the X chromosome has between 800 and 900 genes.

With its limited number, the Y chromosome focuses primarily on male traits. It contains the all-important SRY gene, which instructs the embryo to develop male traits such as testicles.

Another gene unique to the Y chromosome is USP9Y, which contributes to sperm production.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Genetic sex

Question 9. ‘Different genotypes produce the same phenotype’-Justify the statement in the form of a table by taking an example from the result of the dihybrid cross of the Pea plant.
Answer:

The seven pairs of characters as chosen by Mendel

Mating between individuals that differ in only one trait, such as seed color or stem length is known as a monohybrid cross.

In each monohybrid cross, one parent carries one form of the trait, and the other parent carries an alternative form of the same trait. Mendel selected seven such traits to study the monohybrid breeding experiment.

Each trait had two easily distinguishable, alternative appearances (phenotypes).

These are—

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity antagonistic pairs

Experiment And Observation

Mendel carried out a series of monohybrid crosses.

For example, in the spring of 1854, he planted pure-breeding green peas and pure-breeding yellow peas and allowed them to grow into the parental (P) generation.

Later that spring when the plants had flowered, he dusted the female stigma of green-pea plant flowers with pollens from yellow-pea plants. He also performed the reciprocal cross between the female yellow pea plant and the male green pea plant.

In the fall (autumn), when he collected and separately analyzed the progeny peas he found that in both cases, the peas were all yellow.

The yellow peas, the progeny of the P generation, were the beginning of what we now call the first filial (Fx) generation. Mendel planted them and allowed the F₁ plants to self-fertilize.

He then harvested and counted the peas of the resulting second filial (F₂) generation, the progeny of the Fx generation.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity experiment and observation

Among the progeny of one series of F₁ self-fertilization, there were 6022 yellow and 2001 green peas, an almost perfect ratio of 3 yellow to 1 green.

The results of reciprocal crosses produced a similar ratio. Monohybrid crosses involving other traits (such as long and short stem length) also showed similar results.

Question 10. Give your opinion about probable suggestions which can be given to a pair of contenders before marriage in order to prevent the spread of a genetic disease from the society already known to you.
Answer:

Genetic Counselling

Thalassemia mutations and various abnormal hemoglobins interact to produce a wide range of disorders of varying degrees of severity.

Hemoglobin disorders are the most common worldwide inherited conditions. They are common in populations of tropical Africa, Asia, and the Mediterranean region and are spreading by migration throughout the world.

WBBSE Class 10 Life Science Previous Year Papers

A stem cell transplant is the only treatment that can cure thalassemia. But only a small number of people who have severe thalassemias are able to find a good donor match and have the risky as well as expensive procedure.

Genetic counseling, therefore, plays the most important part in thalassemia prevention programs considering the diversity and severity of the problem.

Genetic counseling is defined as the process by which patients or relatives at risk of a disorder that may be hereditary are advised of the consequences of the disorder and the probability of developing and transmitting it and the ways in which this may be prevented.

It Involves The Followings:

A correct diagnosis using genetic tests after evaluation of family history and medical records Explanation of the nature of disorder & the treatment available Estimation of genetic risk for parents and family members.

Communication of genetic risks and the options for avoiding them to avoid undue complications in an unbiased manner Support in making the right decision Accessibility for long-term contact and counseling.

Premarital screening for thalassemia and sickle cell should be made mandatory to decrease at-risk marriages.

The objective is to make people aware of the consequences of thalassemia on health and socio-economics so that they voluntarily ask for screening, and prevention and change their reproductive plans when a possible risk is found.

If the risk is found before marriage, the options are to remain single, not to marry another carrier or to marry irrespective of carrier status.

If the risk is found after marriage, the options are to separate and find a non-carrier partner, to have a few or no children, selective termination of pregnancy, or to take a chance and have children as usual.

There are therefore challenges involved in genetic counseling because all the available choices involve difficult moral and social problems and in most cases, there appears to be no right answer.

But on the other hand, once people understand the risk, they can not escape from making a choice even if the decision ‘not to choose’ is a choice.

Question 11. A good number of Tilapia fishes are released in a pond having only different indigenous fish species grown naturally. Think and write which types of the struggle for existence Tilapia fishes have to face in order to survive.
Answer:

The Tilapia fishes have to face three types of struggle for existence in the pond where they are released.

These are

Intra-specific struggle:

It is the struggle among all the newly released tilapia fishes for food and habitat

Inter-specific struggle:

It is the struggle between Tilapia and other naturally grown indigenous fishes for food and habitat.

Struggle with the environment:

The Tilapia fishes struggle with the condition of the pond where they are newly released. Water content, Temperature of water, amount of dissolved oxygen, poisonous substances present in that pond water, etc. are the obstacles that they struggle, to overcome.

Question 12. Prepare a list of roles air sacs of pigeons play to fly in the air.

Answer:

Importance of air sacs in pigeons:

Pigeon is a primary volant animal. It has nine non-vascular and non-muscular air sacs, emerging from the bronchioles, typically helping in flight.

The importance of air sacs in pigeons is-

During the flight, the pigeon needs extra energy, the production of which requires additional oxygen. Oxygen concentration near the ground level is higher than that in the high sky. Before the flight, pigeons fill the air sacs with this oxygen-rich air. When in the high sky, these air sacs supply oxygen-rich air to the lungs.
The air-filled sacs decrease the specific gravity of the body of the pigeon, which is also beneficial for flight.

Importance of air bladder in rohu fish:

The air bladder in rohu fish helps it to move up and down in the water. The air bladder changes the buoyancy of the body and thus, assists it to go at different depths of water.
The red gland in the anterior chamber of the air bladder fills gas in it to reduce the specific gravity of the body and thus helps the fish to move upward in water. On the other hand, the rete mirabile of the posterior chamber absorbs the gas to increase the specific gravity of the body of fish and helps the fish to go deeper in the water.

WBBSE Class 10 Life Science Previous Year Papers

Question 13.

Structure and function
Indicating the nature of evolution

Based on the above two features establish the concept of the analogous organ with the help of a proper example.

Answer:

Analogous organs are those organs that are different in structure and origin but perform similar functions.

Analogous organs indicate convergent evolution. For example, the wings of birds, wings of insects, and patagium of bats perform the same function, i.e., they help the organisms to fly but they have different structures.

Wings of birds are modifications of forelimbs, wings of insects are an outgrowth of insects’ exoskeleton and the patagium of the bat is actually a fold of skin between forelimbs and hind limbs.

All these structures point toward the fact that in the same environment, different structures may evolve to perform the same function. This further points toward convergent evolution.

Question 14. Relate the following phenomena with the trend of disturbance in the Nitrogen Cycle resulting from different human activities:

Global Warming
Acidification of soil and water of river and lake.

Answer:

Global warming:

Around 40% increase of N₂0 (nitrous oxide) in the environment is due to human activities. N₂0 is released in the environment as a result of the combustion of fossil fuel and the overuse of nitrogen-rich fertilizers.

This N₂O is a greenhouse gas that absorbs infrared radiation or heat of the sunlight which reflects on the earth and facilitates the greenhouse effect and global warming.

Acidification of soil and water of rivers and lakes:

Oxides of nitrogen get dissolved in rainwater and form nitric acid, which is a major component of acid rain. Acid rain destroys aquatic plants and animals and disrupts the ecological equilibrium of rivers lakes, ponds, etc.

Apart from this, the destruction of forest resources and harm to architecture and monuments take place due to acid rain.

Question 15. Hilsa, Bee, Penguin, Rauwolfia- Assess which are the causes of the endangeredness of the above-mentioned organisms.

Answer:

Hilsa:

Facing threat due to overexploitation of this population.

Bee:

Loss of habitat, and excessive use of cell phones that project electromagnetic waves, damage the ability of bees to return to their colony. In that way, it destroys the navigation system of bees.

Penguin:

Penguin faces threats from geological events like a volcanic eruption, pollution, climatic changes, and severe weather.

Rauwolfia:

This type of medicinal plant faces threats due to overexploitation.

WBBSE Class 10 Life Science Model Question Paper 2023

Question 16. Discuss any two roles of the People’s Biodiversity Register (PBR) in conserving local biodiversity.

Answer:

Joint Forest Management or JFM:

The proper management of biodiversity by the joint action of local people and the forest department of the state government which is approved by the Indian government, is known as Joint Forest Management or JFM.

WBBSE Solutions For Class 10 Life Science Chapter 5 Environment Its Resources And Their Conservation Topic D Biodiversity And Conservation forest range office arabari range

Role of JFM in the conservation of biodiversity:

In the conservation of biodiversity, the role of JFM is as follows

The committee, formed by the local residents of any forest area, maintains coordination with the state forest department regarding the conservation of the biodiversity of that forest.
The JFM committee members keep a vigil on the forest area along with their daily activities regarding forest fire, encroaching of the forest area, poaching, felling of trees, etc., and report it immediately to the forest department in case of any adversity.

People’s Biodiversity Register or PBR:

It is a ready reference prepared by the central forest department in accordance with the Biodiversity Law 2002. This document contains detailed information on the availability of local biodiversity, their habits and habitats, other behaviors, their ecological importance, etc.

Role of PBR in the conservation of biodiversity:

In the conservation of biodiversity, the role of PBR is as follows-

PBR provides correct information about the biodiversity of the local areas so that, the rare and endangered animals and plants can be conserved properly.
It makes people aware of the importance of the conservation of biodiversity and involves them directly with the conservation project.
PBR makes the people aware of the sustainable utilization of forest resources and helps in the economic development of the area.
PBR provides correct geographic information about conserved areas.
Identify endangered species and collect information about the conservation of these species.
Gather knowledge about local species and their cultural and social value.
Gives an idea about the obtained product from species and their value along with their collection and transport procedure.

Question 17. Tabulate any of the four activities which are prohibited in a sanctuary following the provisions of the Wildlife Act.

Answer:

The four activities, that are prohibited in the sanctuary are-

Human intervention in the sanctuary is strictly prohibited.
Any human activity which disturbs wild animals is prohibited.
Poaching, hunting, and fishing are strictly prohibited.
Felling of trees is completely prohibited.

WBBSE Class 10 Life Science Model Question Paper 2023

Model Question Paper Life Science Set 1 Group D

Answer 6 questions or their alternatives given below.

Question 1. Draw a neat diagram of the vertical section of the eyeball of the human eye and label the following parts:

In order to be able to learn about and/or solve problems presented to them by their environment, humans must be able to take in information from that environment;

process it quickly and accurately; decide when, how, and what action to take; and then perform or execute that action. In order to receive information from the environment we are equipped with sense organizer

A sense organ is a specialized bodily structure that receives or is sensitive to internal or external stimuli. It is composed of receptors. Human sense organs are the eyes, ears, tongue, skin, and nose.

The Eye As A Sense Organ-Its Location, Structure, And Function

The sense organ consisting of photosensitive receptors (the rod & cone cells) and which helps us in vision is known as the eye.

The two eyes are located in the deep cavities of the skull called orbits on the frontal part of the cranium.

The structure of different parts of the human eye and their corresponding functions are given below:

WBBSE Solutions Chapter 1 Control And Coordination In Living Organisms Topic D Response And Physical Coordination In Animals Nervous system retina

Or,
Explain the importance of the following parts of an eukaryotic chromosome:

Centromere
Telomere

Analyze the role of cell divisions in controlling growth, reproduction, and repair in an organism.

Answer:

The physical structure of eukaryotic chromosomes:

The morphological features of a chromosome appear ‘most distinctly under a microscope during the metaphase stage of cell division. From this study, we can find 5 parts of a chromosome. These parts are described below.

1. Chromatids:

In a metaphase chromosome, two identical and longitudinal strands are seen. These are chromatids. Two chromatids of the same chromosome are called sister chromatids, which remain attached to a constricted region or centromere.

Each chromatid carries one or a few very fine filaments along its length. These are called chromonemata (singular—chromonema). Each chromonema is composed of a longitudinally arranged coiled DNA.

Along each chromonema, several spherical linearly arranged bead-like structures are seen, which are called chronometers.

2. Primary constriction and centromere:

Each chromosome has a distinct constricted region at which the sister chromatids remain attached to each other. This is known as primary constriction.

At e primary constriction, a round plate-like and dense heterochromatin structure is seen, which is called the centromere. The centromere has a few adhesive points, called kinetochores, which attach to the spindle fibers during metaphase.

The DNA present in the .centromere is genetically inactive in nature.

WBBSE Class 10 Life Science Model Question Paper 2023

3. Secondary constriction:

Other than primary constriction, there are one or a few constricted regions in the chromosomes. These are called secondary constrictions. Generally, the nucleolus is seen affixed to the secondary constriction.

During the telophase of cell division, this region helps to reorganize the nucleolus. Therefore, secondary constriction is also known as nucleolar organizer region or NOR.

4. Satellite:

In a few chromosomes, a bulb-shaped terminal portion is seen beyond the secondary constriction. This is called a satellite or SAT body. The chromosomes with SAT body are called SAT chromosomes.

5. Telomere:

The terminal portions of a chromosome are called telomeres. These are genetically inactive regions of a chromosome. During interphase, telomeres help in DNA replication.

It also prevents the joining of a chromosome with another and controls the ageing and death of a cell.

Significance of cell cycle:

The significance of the cell cycle is mentioned below-

1. Controlling cell division:

Certain points of the cell cycle control cell division. These are known as checkpoints. In case of any functional disruption at any of those points, the cell division process becomes uncontrolled, which may lead to tumor formation.

Tumors are of two types-benign tumors and malignant tumors. Benign tumors are harmless but malignant tumor cells invade other tissues through blood or lymph and form tumors there.

This phenomenon is called metastasis, which is a characteristic feature of cancer cells.

2. Normal growth and wound healing:

Cell division helps an organism to grow in size. It also assists in wound healing.

Importance of cell division:

The importance of the cell cycle is given below.

1. Growth:

The number of cells in an organism increases due to cell division. The daughter cells produced by this process also grow in size. Therefore, the growth of any organism depends directly upon cell division.

2. Reproduction:

Amitosis, mitosis, and meiosis help in different types of reproduction processes. Simple unicellular organisms like Amoeba, reproduce by the amitosis process. Mitosis helps in asexual and vegetative reproduction in animals and plants.

By meiotic division, gametes and spores are formed. Therefore, meiosis helps in sexual and asexual reproduction.

3. Wound healing:

Mitosis helps in the repair of wounds and the regeneration of organs in plants and animals.

4. Transfer of genetic characters:

By cell division, the characters of the mother cell are transferred to the daughter cells. From a broader perspective, the newer characters in daughter cells help in adaptation and evolution.

Question 3. Tabulate three pairs of dominant-recessive traits of pea plants as selected by Mendel. State the first law of Mendel as deducted from the experiment of the Monohybrid cross.

Answer :

Three pairs of dominant-recessive traits of pea plant as selected by Mendel

WBBSE Solutions For Class 10 Life Science And Environment Chapter 3 Mendel's Laws And Their Deviation Recessive traits of pea plant as selected by Mendal

Or,
A color-blind female married a normal male. Judge the probability of color blindness among their children in the first filial generation. Show with the help of a cross how the first law of Mendel deviates in the case of the Four-O clock plant in F2 generation.

Answer:

Inheritance of color blindness:

Sex-Linked Inheritance

The gene is located in the sex chromosome. Sex chromosomes may be X or Y chromosomes.

But, as the Y chromosome is more or less genetically inert (functionless or inactive) with respect to the X chromosome, we generally consider sex-linked genes and X-linked genes to be synonymous.

Some X-linked recessive characteristics are- color blindness, hemophilia, etc.

Haemophilia

Haemophilia is a rare disorder in which blood doesn’t clot normally because it lacks sufficient blood-clotting proteins (clotting factors) causing the sufferer to bleed severely even from a slight injury.

Symptoms:

The major signs and symptoms of hemophilia are excessive bleeding and easy bruising.

Children who have mild hemophilia may not have signs unless they have excessive bleeding from a dental procedure, an accident, or surgery,

Bleeding can occur on the body’s surface (external bleeding) or inside the body (internal bleeding)— blood in stool, blood in urine, bruising, nose bleeds, heavy or prolonged periods, etc.

Swollen joints and pain in the joints.

Causes:

A defect in one of the genes that determine how the body makes blood clotting factor VIII or IX causes hemophilia. These genes are located on the X chromosomes.

Chromosomes come in pairs. The two types of hemophilia are factor VIII deficiency (hemophilia A) and factor IX deficiency (hemophilia B, or Christmas disease).

The most common type of hemophilia is called hemophilia A in which the person does not have enough clotting factor VIII (factor eight).

A less common type is hemophilia B in which a person does not have enough clotting factor IX (factor nine). Females have two X chromosomes, while males have one X and one Y chromosome.

Only the X chromosome carries the genes related to clotting factors. Haemophilia usually occurs more in males than in females. About 1 in 5,000 males are born with hemophilia each year.

A male who has a hemophilia gene on his X chromosome will have hemophilia. When a female has a hemophilia gene on only one of her X chromosomes, she does not have symptoms of hemophilia, since at least one of the X- chromosomes have a factor VIII or IX gene that works to produce normal or near normal levels of factors.

Class 10 Life Science Model Paper WBBSE 2023

However, some women who carry this gene may have a bleeding tendency. They are called ‘symptomatic carriers’. They are recognized as having mild hemophilia.

In very rare cases, some women have particularly low factor levels causing them to have moderate or severe hemophilia. In such cases, both X chromosomes are affected or one is affected and the other is missing or inactive.

Inheritance Of Haemophilia:

In this example, the mother is a carrier of the hemophilia gene and the father does not have hemophilia There is a 50% chance that each son will have hemophilia.

There is a 50% chance that each daughter will be a carrier of the hemophilia gene.

In this example, the father has hemophilia and the mother does not carry the hemophilia gene:

None of the sons will have hemophilia All daughters will carry the hemophilia gene In this example, the father does not have hemophilia and the mother does not carry the hemophilia gene

None of the children (either daughters or sons) will have hemophilia or carry the gene.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic B Some Common Genetic Diseases x=choromosomes with haemophilia gene

A Royal Disease:

Haemophilia is sometimes referred to as “the royal disease,” because it affected the royal families of England, Germany, Russia, and Spain in the 19th and 20th centuries.

Queen Victoria of England, who ruled from 1837-1901, is believed to have been the carrier of hemophilia B, or factor IX deficiency. She passed the trait on to three of her nine children.

Her son Leopold died of a hemorrhage after a fall when he was 30. Her daughters Alice and Beatrice passed it on to several of their children.

Alice’s daughter Alix married Tsar Nicholas of Russia, whose son Alexei had hemophilia.

Their family’s entanglement with Rasputin, the Russian mystic, and their deaths during the Bolshevik Revolution have been chronicled in several books and films.

Haemophilia was carried through various royal family members for three generations after Victoria and then disappeared.

Treatment of hemophilia:

Treatment of hemophilia involves regular injections of clotting factor medicine.

Color Blindness

Though most of us share a common color vision sensory experience, some people have a color vision deficiency, which means that their perception of colors is different from what most of us see.

Color-blind people are able to see things as clearly as other people but they are unable to fully ‘see’ red, green, or blue light.

Color blindness is the inability or reduced ability to see colors or to perceive obvious differences between two colors under normal lighting.

Symptoms:

Common symptoms of color blindness include difficulty in distinguishing between colors and inability to see shades or tones of the same color,

People with Red-green color blindness are unable to see some shades of red and green,
People with Blue-yellow color blindness are unable to see some shades of blue and yellow,
People with complete color blindness do not see any colors.

Types:

Color blindness can be mild, moderate, or severe. Based on photo pigments defects in the three different kinds of cone cells that respond to blue, green & red light, color blindness can be of three types

Red-green color blindness:

People with this type of color blindness are unable to see some shades of red and green. Reds may appear brownish-yellow, and greens may look beige to some people.

Certain shades of orange, yellow, and green may appear yellow to others. Red may also appear black to some people. Red-green color blindness is sometimes called Daltonism after John Dalton, the famous scientist, who himself was red-green color blind.

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Blue-yellow color blindness:

People with this type of color blindness are unable to see some shades of blue and yellow. Blue may appear greener and it may be difficult to distinguish yellow and red from pink. Yellow may appear violet to some people.

Complete color blindness:

People with complete color blindness do not see any colors. Poor vision accompanies complete color blindness.

Red-green color blindness is the most common form of color vision deficiency in many parts of the world. It is also much more common in men than in women.

Blue-yellow color blindness affects men and women equally. Complete color blindness is rare.

Causes:

Color blindness is a genetic condition caused by a difference in how one or more of the light-sensitive cells found in the retina of the eye respond to certain colors.

Inherited forms of color blindness often are related to deficiencies in certain types of cones or outright absence of cones.

Usually, genes inherited from the parents cause the deficiency or are responsible for faulty photopigments.

Men are much more likely to be colorblind than women because the genes responsible for the most common, inherited color blindness are on the X chromosome.

Males only have one X chromosome, while females have two X chromosomes. In females, a functional dominant gene for normal vision on only one of the X chromosomes is enough to compensate for the loss on the other.

In X-linked inheritance, the mother carries the mutated gene on one of her X chromosomes and will pass on the mutated gene to 50 percent of her children.

Inheritance of colour blindness:

In X-linked inheritance, the mother carries the mutated gene on one of her X chromosomes and will pass on the mutated gene to 50 percent of her children.

Because females have two X chromosomes, the effect of a mutation on one X chromosome is offset by the normal gene on the other X chromosome.

In this case, the mother will not have the disease, but she can pass on the mutated gene and so is called a carrier.

If a mother is a carrier of an X-linked dis-ease (and the father is not affected), there is a, 1 in 2 chance that a son will have the disease, a 1 in 2 chance that a daughter will be a carrier of the disease, No chance that a daughter will have the disease.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic B Some Common Genetic Diseases XY

Treatment:

In general, treatments include blood transfusions, bone marrow transplants, medications, and supplements, etc.

People who receive blood transfusions receive extra iron that the body can’t easily get rid of and iron can accumulate in tissues, which can be potentially fatal.

The human body has no active mechanism for the excretion of iron.

Excess iron in vital organs, even in mild cases of iron overload, increases the risk for liver disease (cirrhosis, cancer), heart attack or heart failure, diabetes mellitus, osteoarthritis, osteoporosis metabolic syndrome, hypothyroidism, etc.

Hence the treatment of blood transfusion is to be followed with Iron chelation which involves the removal of excess iron from the bloodstream.

Inheritance of thalassemia:

A child who inherits two thalassemia trait genes-one from each parent will have the disease.

A child of two carriers has a 25 percent chance of receiving two trait genes and developing the disease and a 50 per cent chance of being a thalassemia trait carrier.

As illustrated in marriages between two carriers (thalassemia minor) may result in – a 25% chance of thalassemia major children, a 50% chance of thalassemia minor children, and a 25% chance of normal children. Thus two thalassemia carriers should not get married.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic B Some Common Genetic Diseases inheritance of thalassemia

Question 4. Evaluate the effects of the following pollutants on the environment and human health:

Non-biodegradable insecticides
Pollen grain
Chemical fertilizers containing phosphate and nitrate
Wastes containing pathogens originated from health centers
Chlorofluorocarbon

Answer:

Effects of Pollutants on the Environment and human health

WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Topic 2 Environmental Pollution Effects of pollutants on environment and human health

Or,
Speculate the probable causes of each of the following phenomena:

Insomnia, High blood pressure, Partial or Complete deafness
Decrease in the concentration of dissolved oxygen in the water and floating of dead fishes
Decrease in the number of Crocodiles’ Inflammation in the respiratory tract of the lung
Decrease in the number of pollinating insects

Answer:

Probable causes of different phenomena

WBBSE Solutions For Class 10 Life Science And Environment Chapter 5 Topic 2 Environmental Pollution Probable cause of different phenomena

Question 5. ‘The ever-increasing population in the different cities of India is creating the crisis of ground water’-Support the statement with reasons on the basis of your experiences. Construct a concept map to show how the increase in human habitat is influencing the ecosystem of Sunderbans.

Answer:

Groundwater in aquifers below the surface of the earth is an important natural resource. It accounts for nearly 30% of all fresh water.

Class 10 Life Science Model Paper WBBSE 2023

Depletion of groundwater is caused due to the following reasons:

Overuse:

As the population continues to rise, frequent pumping of groundwater causes depletion since it does not have enough time to replenish itself. This has become a major cause in every big city and town.

Agricultural Needs:

Lack of adequate surface irrigation facilities leads to over-exploitation of groundwater to meet crop and livestock requirements. This is a persistent problem in Gangetic Plain and north India.

Anthropogenic pollution:

Groundwater contamination occurs due to the mixing of gas, oil, poisonous salts, and chemicals or pesticides rendering it unsafe.

The environmental effects of groundwater depletion include land subsidence, water shortage, loss of biodiversity, hampered precipitation rate, food shortage, etc.

(or)

Summarise which conservation measures have been adopted to increase the population of an endangered mammal exclusively found in the swampy grasslands under the foothills of the Eastern Himalayas. Discuss the role of biodiversity in maintaining the balance of the ecosystem of a river.
Answer:

Endangered mammal (Red panda) conservation measures:

Since river or lotic ecosystem refers to flowing water, hence biotic components are specialized to live with flow conditions. They include bacteria, primary producers, insects and other invertebrates, fish, and other vertebrates.

Bacteria decompose the organic matter, vegetation, and biofilm. They play a large role in energy recycling.

Primary producers:

These include phytoplanktons, mosses, liverworts, and many rooted plants. These are sources of energy and form microhabitats that shelter other fauna from predators and the water current.

Insects and other invertebrates act both as consumers and prey items in lotic systems.

Various species of fish and other vertebrates like salamanders, snakes, crocodiles, turtles, bird species, and mammals are part of the lotic ecosystem. They act as consumers and also as prey species to the larger vertebrates available.

WBBSE Class 10 Life Science Model Question Paper 2023 Set 1

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity

February 24, 2025June 3, 2023 by vasantha

WBBSE Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Introduction To Heredity and Genetics

All living organisms reproduce. Reproduction results in the formation of offspring of the same kind. A pea plant, for example, produces only pea plants each time it reproduces.

Likewise, a rat produces only rats or humans produce only humans. On the other hand, members of a family share many similarities in appearance, such as height, eye color, hair color, etc.

However, the resulting offspring need not and most often do not resemble the parent. Several characteristic differences do occur between individuals belonging to the same species.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity

It should be noted that the similarities and differences among the members of a species are not coincidental. Both the similarities and differences are received from their parents.

The mechanism of transmission of characters or traits comprising both resemblances as well as differences, from the parental generation to the offspring through reproduction is called heredity.

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WBBSE Chapter 3 Topic A Heredity Introduction To Heredity And Genetics Heredity And Variation

The offspring of all the organisms (plants and animals) resemble their parents in several aspects. This is only due to the phenomenon of heredity.

Heredity is the transmission of characters from one generation to successive generations or from parents to their offspring.

Thus, heredity is the cause of similarities between the offspring, so that the individuals of the same parents resemble each other in many aspects.

Heredity involves the transfer of genetic characteristics from parents to the offspring via the egg and sperm.

On the other hand, though offsprings receive all the characteristics of their parents, still they are not exactly alike.

Heredity Class 10 Life Science

Differences are found even between the offspring of the same parents in terms of the shape of faces, hair color, or even skin color.

It is thus difficult to find identical individuals. The progeny differs not only in itself but also with the parents.

These differences are called variations.

Thus, variations may be defined as the differences (morphological, physiological, cytological, and behavioral) between the parents and the offspring or between the offspring of the same parents, family, and race.

Significance Of Variations:

Variations differentiate one individual from another.

Variations enable individuals to adapt themselves according to the changing environment, ie. they make some individuals better fitted or suited to face the struggle for existence.

Discontinuous variations introduce new traits in the species.

Variations are the key to the evolution and development of new species.

WBBSE Chapter 3 Topic A Heredity Types Of Variation

Primarily Variations May Be Classified Into the Following Two Types:

Hereditary Variation:

The variations that arise as a result of any change in the structure and function of the gene and are inherited from one generation to another are called hereditary variations.

Environmental Variations:

Two individuals with the same genotype may become different in phenotype when they come in contact with different conditions of food, temperature, light, humidity, and other external factors.

Such differences among organisms of similar heredity are known as environmental variation. These are not heritable.

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Variations may also be classified based on the following parameters:

Based On The Type Of Cells Involved,

Variation Is Classified Into Two Types:

Somatic Variation:

The variation which occurs in somatic cells is called somatic variation. It is generally insignificant because it is not inherited from parents.

It is acquired by the organisms during their lifetime and is lost with death. Hence, it is also called acquired variation.

Somatic variations are caused by three types of factors:

Environmental factors include temperature, light, nutrition, water supply, habitat, topography, enemies, etc.

Use & disuse of organs as may be found in singers whose vocal organs are far more developed than the non-singers.

Conscious efforts include receiving education, developing certain good or bad, or unhealthy habits, etc.

Germinal Variation:

The variation which affects the germinal or reproductive cells is called germinal variation. It is heritable and genetically significant.

It provides raw materials for evolution.

Heredity Class 10 Life Science

The factors that cause germinal variations include chance separation of chromosomes, a chance combination of chromosomes, crossing over, chromosomal aberrations, change in chromosome number, genetic mutations, etc.

Based On The Degree Of Differences, Variation Is Classified Into Two Types:

Continuous Variation:

Small and indistinct variations are called continuous variations, eg. the shape of the nose or the color of the skin, etc.

These fluctuate with environmental conditions.

These are non-heritable.

They have no role in evolution.

They are most common and occur in all organisms or races of a species.

Discontinuous Variation:

Large, distinct, and sudden variations are called discontinuous variations, or mutations, eg. the appearance of six fingers in a man, polydactyly, etc.

These are relatively unaffected by environmental conditions.

These are mostly heritable. However, not all the discontinuous variations pass to the next generations because of their appearance in the body cells after the differentiation of germ cells.

They provide raw materials for evolution on which selection is based.

They are not common and appear suddenly.

Based on the affected traits, variations may be of four types:

Morphological variation:

These are the differences that are found in the form and structure of organisms.

Physiological variation:

These are the variations observed in various functions of the body like BMR etc.

Cytological variation:

These variations occur in the number of cells, cell constituents, and their products.

Behaviouristic variation:

These variations are connected with the behavior of the organisms towards different conditions.

Based on impact, variations are of three types:

Beneficial Variation:

These are the variations that help the organisms skillfully adapt to the particular environment.

Heredity Class 10 Life Science

Harmful variations:

These variations make organisms unfit for their environment.

Neutral variations:

These variations do not affect the organisms in any way.

WBBSE Chapter 3 Topic A Heredity Sources Of Variation

Variations are more pronounced in sexually reproducing organisms. In sexual reproduction, the production of offspring takes place by the fusion of two types of gametes.

These gametes are formed by the reduction division. Thus, sexual reproduction introduces unlimited genetic variation into the population. The more closely related the sexual partners are, the lesser the variations in their offspring.

Common sources of variations are-

Recombination:

Recombination results in offspring that have a combination of characteristics different from that of their parents. Different types of combinations of characters bring about variation.

Crossing Over:

At the time of gamete formation, crossing over occurs during meiosis division, which causes variations in genetic characteristics.

Mutation:

It is a spontaneous, sudden, heritable, and permanent change in genetic characteristics that causes a detectable effect in the organisms. It occurs in nature or it can be caused artificially in an organism.

WBBSE Chapter 3 Topic A Heredity Mendel The Father Of Genetics

There have been several explanations on the possible mechanism of inheritance of traits from the parent to the offspring, put forth from time to time by different biologists.

All these early theories presume that the characteristics of the two parents somehow mix during inheritance. Hence these ideas came to be known as blending theories of inheritance.

Gregor Johann Mendel (1822-1884) was born in a family of poor peasants in Moravia, Austria. He received his school education with utmost difficulty due to poverty in the family.

Wbbse Class 10 Life Science Heredity Notes

In 1843 he joined a church as a monk where, in 1847, he became the abbot (head) of the monastery at Brunn, Austria (now called Bruno in Czechoslovakia).

In addition to his normal duties of preaching in the church, Mendel evinced a keen interest in the maintenance of the garden in the premises of the church.

In the course of his routine rounds in the garden, Mendel was keenly observing the pattern of inheritance of certain characters in some of the plants.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Mendel the father of genetics

He became interested in investigating the mechanism by which the characters are transferred from the parent plants to their offspring. He decided to conduct some experiments in this direction.

After careful examination and thinking, Mendel selected the pea plants (Pisum sativum) for his experiments.

Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance.

He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits.

He recognized the mathematical patterns of inheritance from one generation to the next.

Thus, Mendel’s concept gave birth to the particulate theory of inheritance. Mendel’s excellent experiments, valid mathematical analysis, and formulation of laws of inheritance are collectively known as Mendelism.

The genetic experiments Mendel did with pea plants took him eight years (1856-1863) and he published his results in 1865. During this time, Mendel grew over 10,000 pea plants, keeping track of progeny number and type.

Wbbse Class 10 Life Science Heredity Notes

Mendel’s work and his Laws of Inheritance were not appreciated in his time. As a result, Mendel died in 1884 without any sort of recognition.

It was not until 1900, after the rediscovery of his Laws, that his experimental results were understood.

Three botanists – Hugo DeVries, Carl Corrensand Erich von Tschermak – independently rediscovered Mendel’s work in the year 1900, a generation after Mendel published his papers.

They helped expand awareness of the Mendelian laws of inheritance in the scientific world. The three Europeans, unknown to each other, were working on different plant hybrids when they each worked out the laws of inheritance.

WBBSE Chapter 3 Topic A Heredity Hereditary Variation

The variations that arise as a result of any change in the structure and function of the gene and that are inherited from one generation to another are called hereditary variations.

The ultimate source of all genetic variation is mutation. It leads to changes in gene function and permanent alteration to the DNA sequence.

It is a rare, random change in the genetic material and it can be inherited. The permanent alteration in the DNA sequence that makes up a gene results in difference which is found in most people.

Mutations range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes.

This is the only way new alleles (varieties of a gene) are produced. Mutations are rare events: the average rate of mutation is about one per 100,000 genes.

Wbbse Class 10 Life Science Heredity Notes

Thus it would take on average 100,000 generations for a mutation to occur at any one specific gene. However, each individual has many, many functional genes.

Thus, at the level of the whole individual, mutations occur quite often. It is estimated that each human gamete (egg or sperm cell) has, on average, one mutation.

The heritable change in the composition of a gene that leads to the formation of a mutant gene having changed function and with the consequent appearance of a new phenotype is known as mutation.

Types Of Mutations:

There Are Two Types Of Mutations:

Gene mutations or point mutations, and

Chromosomal mutations.

1. Gene mutations:

A chemical change that occurs in the DNA of a cell is called a gene mutation or point mutation. Such a mutation may alter the sequence of the nucleotides within a part of the DNA molecule.

This alternation changes the information of the DNA chain and results in differences in the proteins being produced.

For Example:

In sickle cell anemia, the mutation of a single gene causes a slight change in the structure of the protein molecule of hemoglobin, and because of that slight change, the blood cell that carries the hemoglobin takes a sickle shape.

According to many scientists, the mutations may be caused naturally by the radiation that constantly enters the earth’s atmosphere from the cosmos.

For example, gene mutations are probably caused when the sex cells (gametes) of an organism are exposed to X-rays, gamma rays, cosmic rays, and ultraviolet rays. In addition to this radiation, certain chemicals called mutagens can change nucleotides within DNA molecules.

Wbbse Class 10 Life Science Heredity Notes

The chance for a particular human gene to mutate in one generation is about 1 in 10,000 to 1 in 1,000,000. Since humans have at least 30,000 genes, each person likely carries at least one mutation.

2. Chromosomal Aberrations (Chromosome mutations):

Another way for the genetic traits of an organism to be altered is through changes involving whole chromosomes or parts of chromosomes.

Structural changes in chromosomes are also caused by radiation, chemicals, and even some virus infections.

Chromosomal mutations may be of two basic types-

Change of structure, and
Change of number.

Chromosome structure changes:

Changes occur in the structure of chromosomes, during cell division. When homologous chromosomes pair up, linked genes on the chromosomes may break apart. The genes may join another chromosome, or they may be lost.

Thus, a deletion involves the loss of a piece of chromosome.

If a chromosome breaks and the parts do not reattach, the pieces may be lost. This is the most serious kind of chromosome mutation. Here, bits of genetic information are not available to the offspring.

Duplication occurs when one extra, but identical piece of a chromosome is added to the normal chromosome When an inversion occurs, the pieces of chromosomes break apart and pieces rejoin the same chromosome in a different order. Usually, inversions have no harmful effects on the offspring.

The joining of a fragmented chromosome to a non-homologous chromosome is a translocation. The piece of chromosome detaches from one chromosome and moves to a new position on another chromosome.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Deletion

Chromosome number changes:

A chromosome mutation that causes individuals to have an abnormal number of chromosomes is termed aneuploidy. Aneuploid cells occur as a result of chromosome breakage or non-disjunction errors that happen during meiosis or mitosis.

Non-disjunction is the failure of homologous chromosomes to separate properly during cell division. It produces individuals with either extra or missing chromosomes.

Sex chromosome abnormalities that result from non-disjunction can lead to conditions such as Klinefelter and Turner syndromes. In Klinefelter syndrome, males have one or more extra X chromosomes.

In Turner syndrome, females have only one X chromosome. Down syndrome is an example of a condition that occurs due to non-disjunction in autosomal (non-sex) cells. Individuals with Down syndrome have an extra chromosome on autosomal chromosome 21.

Mendel’S Laws Of Heredity Class 10

A chromosome mutation that results in individuals with more than one haploid set of chromosomes in a cell is termed polyploidy. A haploid cell is a cell that contains one complete set of chromosomes.

Our sex cells are considered haploid and contain 1 complete set of 23 chromosomes. Our autosomal cells are diploid and contain 2 complete sets of 23 chromosomes.

If a mutation causes a cell to have three haploid sets, it is called triploidy. If the cell has four haploid sets, it is called tetraploidy.

Due to the mutagens, two types of mutations are found visible and lethal mutations. Mutations are located on either sex chromosomes or autosomes.

Common Variations In Human Population

Some examples of often un-noticed human traits are the ability or inability to roll the tongue, attached or unattached earlobes, dimples or freckles, naturally curly or straight hair, smooth or cleft chin, color blindness or normal vision, etc.

There are numerous traits in humans, but some traits occur more frequently than others. Between 70-90% of the human population have free-hanging earlobes, can roll their tongue, are right-handed, and can taste a chemical called PTC (Phenyl-thio-carbamide).

But these characters have nothing to do with life efficiencies.

Some common examples are-

Ear Lobe:

Some people have earlobes that curve up between the lowest point of the earlobe and the point where the ear joins the head; these are known as “free” or “unattached” earlobes.

Other people have earlobes that blend in with the side of the head, known as “attached” or “adherent” earlobes [Fig 3.3(b)]. Attached vs.

free earlobes are often used to illustrate basic genetics. The major form of the gene that determines the shape of the earlobe is known as an allele. An allele is a gene that is found at a specific position on a chromosome.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Attached and detached

If the genes from the parents get expressed by the dominant allele, then the child will be born with free earlobes.

The structural formation of the attached earlobe is due to the absence of the dominant allele in the chromosomes. The recessive allele is expressed in the chromosomes to form an attached earlobe.

Thus, if a person is homozygous recessive for this trait, the earlobes attach directly to the head and do not hang free. However, it is not necessary that parents with attached earlobes should give birth only to the attached earlobe child.

If, on the other hand, parents with free earlobes give birth to a baby with attached earlobes, it is certain that both of them have a copy of the dominant and recessive alleles.

Tongue Rolling:

Tongue rolling is the ability to roll the lateral edges of the tongue upwards into a tube. A dominant allele enables some people to roll their tongues into a distinct U-shape. If you cannot roll your tongue you carry the recessive trait.

Recent studies have shown that this tongue-rolling could be dependent on multiple genes or alleles & some kind of environmental influences.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity u shaped tounge.jpg

WBBSE Chapter 3 Topic A Heredity Key Terms Associated With Heredity

Some basic key terms associated with heredity and genetics are—

Characteristics Or Trait:

A characteristic or phenotypic trait, or simply trait, is a distinct variant of a phenotypic characteristic of an organism that may be inherited, environmentally determined, or maybe a combination of the two.

For example, eye color is a character or abstraction of an attribute, while blue, brown, and hazel are traits.

Individuals and groups differ among themselves biologically, in a practically endless succession of more or less visible elements of their descriptions, which are named as traits, features, marks, nature, characteristics, characters, and others.

Mendel’s Laws Of Heredity Class 10

Each of these components is a description of, say, the observational nature, i.e. selected part of our vision or measuring the actual condition of the individual body or group structure.

Allele:

An allele is an alternative or some form of a gene (one member of a pair) that is located at a specific position (locus) on a specific chromosome.

These DNA codings determine distinct traits that can be passed on from parents to offspring through sexual reproduction. Alleles may occur in pairs, or there may be multiple alleles affecting the expression (phenotype) of a particular trait.

The word “allele” is a short form of allelomorph (“other form”), which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes.

Organisms generally have two alleles for each trait, for example- yellow or green seed colors of pea plants; in humans, the gene for eye color has an allele for blue eye color and an allele for brown.

For any gene, a person may have the same two alleles or two different ones.

Locus:

In genetics, a locus (plural loci) is the specific location of a gene, DNA sequence, or position on a chromosome.

Each chromosome carries many genes; in humans, the estimated number of ‘haploid’ protein-coding genes is 20,000-25,000, located on 23 different chromosomes. A variant of a similar DNA sequence located at a given locus is called an allele.

A locus is the specific physical location of a gene or other DNA sequence on a chromosome, like a genetic street address.

A locus is a spot or “address” on a chromosome at which a gene for a particular trait is located in all members of a species. It can also refer to the location of a mutation or other genetic marker.

A given locus can be found on any pair of homologous chromosomes. For example, in Drosophila, the locus of red and white eye colors is present on the X chromosome.

Unit of inheritance (Factor/Gene):

A gene is a stretch of DNA that helps to control the development and function of all organs and working systems in the body.

Mendel didn’t know about genes or discover genes, but he did speculate that there were two factors for each basic trait and that 1 factor was inherited from each parent.

We now know that Mendel’s inheritance factors are genes (the term was first used by Johannsen, 1909), or more specifically alleles – different variants of the same gene. It is now known that Mendelian factors, determinants, or genes are present in a linear sequence on the chromosomes.

Therefore, the gene is also defined as a unit of inheritance that consists of linear chromosome segments that can be assigned to the expression of a particular Character.

Mendel’s Laws Of Heredity Class 10

Its effect is, however, influenced by its allele, other genes, and the environment.

Genes are passed from parent to offspring; the combination of these genes affects all aspects of the human body, from eye and hair color to how well the liver can process toxins.

Monohybrid and dihybrid cross:

A monohybrid cross is a breeding experiment between P-generation (parental generation) organisms that differ in one trait.

It is a genetic cross between parents that differ in the alleles they possess for one particular gene, one parent having two dominant alleles and the other two recessives.

All the offspring (called monohybrids) have one dominant and one recessive allele for that gene (i.e. they are hybrid at that one locus). Generally, the monohybrid cross is used to determine the dominance relationship between two alleles.

Example:

The allele for green pod color is dominant and the allele for yellow pod color is recessive. The cross-pollination between a P-generation green pod pea plant and a P-generation yellow pod plant results in all green offspring.

Crossing between these offspring yields a characteristic 3:1 (monohybrid) ratio in the following generation of dominant recessive phenotypes.

A dihybrid cross is a cross between two pure lines (varieties, strains) that differ in two observed traits. A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits.

A hybrid organism is heterozygous, which means that it carries two different alleles at a particular genetic position or locus.

Therefore, a dihybrid organism is heterozygous at two different genetic loci. Mendel used these results as the basis for his Law of Independent Assortment.

Example:

Mendel performed a dihybrid cross using pea plants and the characteristics of seed color and texture: the parental plants had either smooth yellow seeds- the dominant characteristics – or wrinkled green seeds- the recessive characteristics.

All the offspring had smooth yellow seeds, being heterozygous for the two alleles. Crossing between these offsprings produced an F₂ generation of plants with smooth yellow, smooth green, wrinkled yellow, and wrinkled green seeds in the ratio of 9:3:3:1.

Homozygous and heterozygous organisms:

Organisms can be homozygous or heterozygous for a gene. Homozygous means that the organism has two copies of the same allele for a gene.

An organism can be homozygous dominant if it carries two copies of the same dominant allele, or homozygous recessive if it carries two copies of the same recessive allele.

Heterozygous means that an organism has two different alleles of a gene. For example, pea plants can have red flowers and either be homozygous dominant (red-red), or heterozygous (red-white).

If they have white flowers, then they are homozygous recessive (white-white). Carriers are always heterozygous.

Example:

An organism is referred to as being homozygote or homozygous at a specific locus when it carries two identical copies of the gene affecting a given trait on the two corresponding homologous chromosomes (e.g., the genotype is PP or pp when P and prefers to different possible alleles of the same gene).

Such a cell or such an organism is called a homozygote.

An organism is a heterozygote or is heterozygous at a locus or gene when it has different alleles occupying the gene’s position in each of the homologous chromosomes.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity genotype

In diploid organisms, the two different alleles are inherited from the organism’s two parents. For example, a heterozygous individual would have the allele combination Pp.

Hybridization:

Genetic hybridization is the process of interbreeding individuals from genetically distinct populations to produce a hybrid. A genetic hybrid would therefore carry two different alleles of the same gene.

During the 20th century planned hybridization between carefully selected parents has become dominant in the breeding of self-pollinated species.

The object of hybridization is to combine desirable genes found in two or more different varieties and to produce pure-breeding progeny superior in many respects to the parental types.

The process of hybridization is important biologically because it increases the genetic variety (number of different gene combinations) within a species, which is necessary for evolution to occur.

Mendel’s Laws Of Heredity Class 10

Example: Hybridization is the process of crossing two genetically different individuals to create new genotypes.

For example, a cross between parent 1, with the genetic makeup (genotype) BB, and parent 2, with bb, produces progeny with the genetic makeup Bb, which is a hybrid (the first filial generation or FI).

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity hybridization

Hybridization was the basis of Gregor Mendel’s historic experiments with garden peas. Inheritance studies require crossing plants with contrasting or complementary traits.

Pure and hybrid:

A diploid organism has paired chromosomes, each with a similar arrangement of genetic loci.

Variations of these genes are called alleles. If an organism has one of the same types of alleles on each of its chromosomes, that organism has a pure trait.

If an organism has two different types of alleles on its chromosomes, that organism has a hybrid trait. Pure breed or true breeding are individuals that are homozygous and that will always produce the same offspring when crossed together.

A hybrid is an organism that has two different alleles for a trait.

In the simplest possible terms, purebreds are the offsprings that result from mating between genetically similar parents while hybrids are the offsprings that are the result of mating between two genetically dissimilar parents.

Thus, purebreds are composed of two (or more) like components while hybrids are created using two or more similar but not like components.

Parental generation:

The parental generation (P) is the first set of parents crossed. It is the generation of individuals of different genotypes that are mated, usually for scientific purposes, to produce hybrids.

These parental strains are purified and obtained by repeated cycles of self-fertilization. In a parental generation, two individuals are mated or crossed to determine or predict the genotypes of their offspring, called the first filial generation.

Immediate parents are designated as Pv grandparents P2; great grandparents are P3 and so on.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity parent generation

Filial generation:

Filial generation is the offspring generation. It is a generation in a breeding experiment that is successive to mating between parents of two distinctively different but usually relatively pure genotypes.

F₁is the first offspring or filial generation; F₂ is the second; and so on.

Successive generations of progeny result in a controlled series of crosses, starting with two specific parents (the P generation) and selfing or intercrossing the progeny of each new (F₁F₂; etc. ) generation.

Filial 1 (F₁) generation is the one resulting from the cross of such two selected parent generations; this generation expresses a high degree of uniformity (hybrids).

The progeny/generation derived from the Filial 1 generation is termed the Filial 2 generation (F₂); this generation can show a very high degree of variation from progeny to progeny depending upon the parental generation used.

Dominant and recessive characteristics:

The terms dominant and recessive describe the inheritance patterns of certain traits. Sexually reproducing species, including people and other animals, have two copies of each gene.

The two copies, called alleles, can be slightly different from each other. The differences can cause variations in the proteins that are produced.

Proteins affect traits, so variations in protein activity or expression can produce different phenotypes. A dominant allele produces a dominant phenotype in individuals who have one copy of the allele, which can come from just one parent.

For a recessive allele to produce a recessive phenotype, the individual must have two copies, one from each parent.

An individual with one dominant and one recessive allele for a gene (heterozygous) will have the dominant phenotype.

Heredity Class 10 Life Science

For example, in humans, the allele for brown eyes is dominant, therefore offspring only need one copy of the ‘brown eye’ allele to have brown eyes (although, with two copies they will still have brown eyes).

Recessive alleles only show their effect if the individual has two copies of the allele (also known as being homozygous).

For example, the allele for blue eyes is recessive, therefore to have blue eyes the offsprings need to have two copies of the ‘blue eye’ allele.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity brown eyes

Phenotype And Genotype:

Genotype is the genetic makeup of an individual organism that functions as a set of instructions for the growth and development of the body.

The word ‘genotype’ is usually used when talking about the genetics of a particular trait (like eye color).

Phenotype is the observable physical or biochemical characteristics of an individual organism, determined by both genetic makeup and environmental influences, for example, height, weight, and skin color.

An organism’s genotype is the set of genes that it carries. An organism’s phenotype is all of its observable characteristics—which are influenced both by its genotype and by the environment.

The “internally coded, inheritable information”, or Genotype, carried by all living organisms, holds the critical instructions that are used and interpreted by the cellular machinery of the cells to produce the “outward, physical manifestation”, or Phenotype of the organism.

The entire set of genes or the genotype in a black mouse. It comprises a set of alleles that determines the expression of a particular characteristic or trait (phenotype). Her black hair is the trait or phenotype concerned.

All the key terms described in this article (3A.2), are explained with sample crosses in the following articles.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity genotype and phenotype

WBBSE Chapter 3 Topic A Heredity Mendel’s Work On Pea Plants

In 1854, Mendel began a series of breeding experiments with the garden pea Pisum sativum in an attempt to learn something about the mechanisms of heredity.

The bisexual flower of pea normally reproduces by self-fertilization.

That is, the stamen (male reproductive organs) produces pollens, which land on the pistil (female reproductive organs) within the same flower and consequently fertilize the plant. This process is called selfing.

To prevent selfing and to carry out cross-pollination in pea plants, three steps of emasculation, dusting and bagging are to be carried out as elaborated here:

It is relatively a simple procedure to prevent self-fertilization of the pea by removing the stamens from a developing flower bud before they produce any mature pollen.

For this purpose, the stamens are cut off by a scissor from the selected bisexual flowers to remove the masculine part of the flower.

This process is known as emasculation. The pollen taken from the stamens of another flower can then be dusted onto the stigma of the pistil of the emasculated one to cross-pollinate it. After cross-pollination, all the

flowers are covered with paper bags to avoid any contamination by undesired pollen grains.

Cross-fertilization, or more simply a cross, is the term used for the fusion of male gametes (pollen) from one individual and female gametes (eggs) from another.

Once cross-fertilization has occurred, the zygote develops in the seeds (peas), which are then planted.

For his experiment, Mendel obtained 34 strains of pea plants that differed in a number of traits.

He allowed each strain to self-fertilize for many generations to ensure that he only worked with pea strains in which the trait under investigation remained unchanged from parent to offspring for many generations.

Wbbse Class 10 Life Science Heredity Notes

Such strains are called true-breeding or pure-breeding strains.

In Mendel’s work true breeding or pure breeding homozygous strains constitute the parental (P) generation.

Once cross-fertilization is carried out in a parental generation, the progeny that is obtained is known as the First generation offspring or First filial (F₁) generation.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity parental generation

WBBSE Chapter 3 Topic A Heredity Mendel’s Experiment And Laws For Monohybrid Cross

Mendel performed several mono-hybridization experiments on pea plants involving crosses between parents that differ in a single gene.

WBBSE Chapter 3 Topic A Heredity The seven pairs of characters as chosen by Mendel

Mating between individuals that differ in only one trait, such as seed color or stem length is known as a monohybrid cross.

Each trait had two easily distinguishable, alternative appearances (phenotypes).

These are—

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity antagonistic pairs

WBBSE Chapter 3 Topic A Heredity Experiment And Observation

Mendel carried out a series of monohybrid crosses.

For example, in the spring of 1854, he planted pure-breeding green peas and pure-breeding yellow peas and allowed them to grow into the parental (P) generation.

In the fall (autumn), when he collected and separately analyzed the progeny peas he found that in both cases, the peas were all yellow.

The yellow peas, the progeny of the P generation, were the beginning of what we now call the first filial (Fx) generation. Mendel planted them and allowed the F₁ plants to self-fertilize.

He then harvested and counted the peas of the resulting second filial (F₂) generation, the progeny of the Fx generation.

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity experiment and observation

Among the progeny of one series of F₁ self-fertilization, there were 6022 yellow and 2001 green peas, an almost perfect ratio of 3 yellow to 1 green.

The results of reciprocal crosses produced a similar ratio. Monohybrid crosses involving other traits (such as long and short stem length) also showed similar results.

WBBSE Chapter 3 Topic A Heredity Mendel’s explanation

To explain these results, Mendel proposed the existence of what he called particulate unit factors for each trait. He suggested that these factors served as the basic unit of heredity and passed unchanged from generation to generation, determining various traits expressed by each individual plant.

WBBSE Chapter 3 Topic A Heredity Mendel’s First Three Postulates

Using the constant pattern of result in the monohybrid crosses, Mendel derived the following three postulates or principles of inheritance

Unit Factors in Pairs:

Genetic characters are controlled by unit factors existing in pairs in individual organisms.

In the monohybrid cross involving yellow (Y) and green (y) seeds, a specific unit factor exists for each trait. Each diploid individual receives one factor from each parent.

Because the factors occur in pairs, three combinations are possible:

YY, Yy, and Yy. The seeds having unit factor combinations of either YY or yy have two copies of the same allele for a gene. Hence these are homozygous.

The seeds having a unit factor combination of Yy have two different alleles of a gene. Hence these are heterozygous.

Dominance/Recessiveness:

When two unlike unit factors, responsible for a single character, are present in a single individual, one unit factor is dominant to the other, which is said to be recessive.

In each monohybrid cross, the trait expressed in the F₁ generation results from the presence of the dominant unit factor.

The trait that is not expressed in the F₁ but which reappears in the F₂ is under the genetic influence of the recessive unit factor.

In the above-mentioned case, the trait yellow seed color (Y) is said to be dominant to the recessive trait, green seed (y). Hence, the progeny of P, i.e. the F₁ generation had all yellow pea plants.

Among the progeny of ie. in the F₂ generation, green pea plants reappeared along with yellow pea plants.

Segregation:

During the formation of gametes, the paired unit factors responsible for contrasting traits do not blend with each other but separate or segregate randomly, so that each garnet receives one or the other with equal likelihood.

This is known as the 1st law of Mendel or the law of Segregation.

WBBSE Chapter 3 Topic A Heredity Analysis Of Monohybrid Cross And Checker Board

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Analysis of monohybrid cross

WBBSE Chapter 3 Topic A Heredity Punnett Squares

The genotypes and phenotypes resulting from the recombination of gametes during fertilization can be easily visualized by constructing a Punnett square, named after R. C.

Punnett who first devised this approach. In this construction, each of the possible gametes is assigned an individual column or a row, with the vertical column representing those of the female parent and the horizontal row those of the male parent.

After the gametes are entered in rows and columns, the new generation can be predicted by combining the male and female gametic information for each combination and entering the resulting genotype in the boxes. This process represents all possible random fertilization events.

WBBSE Chapter 3 Topic A Heredity Mendel’s Experiment And Laws For Dihybrid Cross

WBBSE Chapter 3 Topic A Heredity Experiment and Observation

Mendel-crossed pea plants that are heterozygous for two genes at the same time.

To construct such a dihybrid, he mated true-breeding plants grown from yellow round peas (YYRR) with true-breeding plants grown from green wrinkled peas (year).

Explanation

From the observed ratios, Mendel inferred the biological mechanism of shuffling the independent assortment of gene pairs during gamete formation.

Because the genes for peas’ color and for shape assort independently, Y can be with R or r in any gamete with equal probability.

Thus, the presence of a particular allele of one gene, say, the dominant Y for pea color, provides no information whatsoever about the alleles of the second gene.

That is, the allele for pea shape in Y carrying game could with equal likelihood be either R or r.

Each dihybrid of the F₁ generation can, therefore, make four kinds of gametes:

YR, Yr, yR, and yr. In a large number of gametes, the four kinds will appear in an almost perfect ratio of 1:1:1:1.

At fertilization then, in a mating of dihybrids, 4 different kinds of eggs can combine with any one of 4 different kinds of pollen, producing a total of 16 possible zygotes in the F₂ generation.

Wbbse Class 10 Life Science Heredity Notes

Once again, a Punnett square is a convenient way to visualize the process.

In fact, there are only nine different F₂ genotypes — YYRR, YYRr, YyRr, YyRR, yyRR, yyRr, YYrr, Yyrr, and yyrr — because the source of the alleles (egg or pollen) does not make any difference.

If, however, we look at just pea color or just pea shape, we can see that each trait is inherited in the 3: 1 ratio as predicted by Mendel’s law of segregation.

Punnet Square or Checker Board of Dihybrid cross

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity Punnet Square or Checker Board of Dihybrid cross

WBBSE Solutions For Class 10 Life Science Chapter 3 Heredity And Common Genetic Diseases Topic A Heredity f2 generation

WBBSE Chapter 3 Topic A Heredity Mendel’s Fourth Postulate

The above analysis became the basis of Mendel’s second general principle or the fourth postulate, the law of independent assortment.

Independent Assortment:

During gamete formation, segregating pairs of unit factors assort independently of each other and undergo random recombination in all possible combinations governed by chance alone.

WBBSE Chapter 3 Topic A Heredity Reasons for Mendel’s Success