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Page No 191:

Question 1:

Which of the processes, sexual reproduction or asexual reproduction, bring about maximum variations in the offsprings?

Answer:

Maximum variations in the offsprings occur in the process of sexual reproduction.

Page No 191:

Question 2:

Name one variation in humans connected with ears.

Answer:

In ears, free earlobes and attached earlobes are an example of variation in humans.

Page No 191:

Question 3:

What constitutes the link between one generation and the next?

Answer:

Gametes constitute the link between one generation and the next. They pass on the paternal and maternal characteristics to the offspring.

Page No 191:

Question 4:

If the trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?

Answer:

Trait B is likely to have arisen earlier, as it is prevalent in a greater proportion in the population.

Page No 191:

Question 5:

Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors?

Answer:

The modern name of these factors is genes.

Page No 191:

Question 6:

Some plants occur in one of the two sizes : tall or dwarf. This characteristic is controlled by one pair of genes. Tallness is dominant to dwarfness. Choose suitable letters for this gene pair.

Answer:

Let 'T' stands for tall, and 't' stand for dwarf. Hence, the gene pair will be Tt.

Page No 191:

Question 7:

What are the chromosomes XY and XX known as?

Answer:

Chromosomes XY and XX are known as sex chromosomes.

Page No 191:

Question 8:

Which of the two, sperm or ovum, decides the sex of the child?

Answer:

The sperm decides the sex of a child.

Page No 191:

Question 9:

State whether the following statement is true or false :
The sex of an infant is not a case of inheritance of characteristics.

Answer:

False. The sex of an infant is a case of inheritance of characteristics. This is because an infant's sex is determined by the sex chromosomes that come from parents.

Page No 191:

Question 10:

A new born child has an XY pair of chromosmes. Will it be a baby boy or a baby girl?

Answer:

The child will be a boy.

Page No 191:

Question 11:

Which of the following combinations of sex chromosomes produce a male child : XX or XY?

Answer:

Combination XY of sex chromosomes produces a male child.

Page No 191:

Question 12:

Name the first scientist who studied the inheritance of traits from one generation to the next.

Answer:

Gregor Mendel was the first scientist, who studied the inheritance of traits from one generation to the next.

Page No 191:

Question 13:

What type of plants were used by Mendel for conducting his experiments on inheritance?

Answer:

Mendel used different varieties of pea plants (Pisum sativum) for conducting his experiments on inheritance.

Page No 191:

Question 14:

The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father?

Answer:

The hair colour of the person will be black because the gene for red hair is recessive compared to black.

Page No 191:

Question 15:

What are the four blood groups in humans?

Answer:

The four blood groups in humans are A, B, AB and O.

Page No 191:

Question 16:

Name one reptile in each case where higher incubation temperature leads to the development of : (a) male progeny, (b) female progeny.

Answer:

(a) Lizard (Agama agama)
(b) Turtle (Chrysema picta)

Page No 191:

Question 17:

Fill in the following blanks with suitable words :
(a) Genes always work in ................ .
(b) In pea plants, the gene for dwarfness is ..............whereas that for tallness is ............ .
(c) Most people have ............earlobes but some have ............earlobes.
(d) A human gamete contains.............. chromosomes whereas a normal body cell has .......... chromosomes in it.
(e) All races of man have...........blood groups.
(f) The...............chromosomes for a ............are XX whereas that for a ..............are XY.

Answer:

(a) Genes always work in pairs.
(b) In pea plants, the gene for dwarfness is recessive, whereas that for tallness is dominant.
(c) Most people have free earlobes but some have attached earlobes.
(d) A human gamete contains 23 chromosomes, whereas a normal body cell has 46 chromosomes in it.
(e) All races of man have different blood groups.
(f) The sex chromosomes for a female are XX, whereas that for a male are XY.



Page No 192:

Question 18:

Which of the following represent tall plants and which represent short plants (or dwarf plants)?
(a) Tt
(b) tt
(c) TT
Give reason for your choice (The symbols have their usual meaning).

Answer:

(a) Tt represents tall plants, as T (tall) is dominant over t (dwarf).
(b) tt represents dwarf plants, as t (dwarf) is present in homozygous recessive state.
(c) TT represents tall plants, as T (tall) is present in homozygous dominant state.

Page No 192:

Question 19:

A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter?

Answer:

The answer to this question depends on whether the blood group B of the woman has gene combination IBIB or IBIO.
In the first case (i.e., when the blood group B has genotype IBIB), the daughter will have blood group B. This is because here the gene IB is dominant over gene IO.
In the second case (i.e., when the blood group B has genotype IBIO), there stands an equal chance for the genotype of the daughter's blood to be either IBIO or IOIO. Due to this, there is an equal chance for the daughter to acquire blood group B or blood group O.

Page No 192:

Question 20:

(a) Name the scientist who gave the laws of inheritance.
(b) Name an animal in which individuals can change sex. What does this indicate?

Answer:

(a) Gregor Mendel gave the laws of inheritance.
(b) Snail is an example of an animal that can change sex. This indicates that sex in snails is not determined genetically.

Page No 192:

Question 21:

Explain with an example, how genes control the characteristics (or traits).

Answer:

A gene is the section of DNA on a chromosome that codes the formation of a protein controlling a specific characteristic of the organism.
Suppose, a plant progeny possesses gene for the characteristic called 'tallness'. The gene for tallness will give instructions to the plant cells to generate many plant-growth hormones due to which the plant will grow tall. On the other hand, if the plant has the gene for shortness, less plant-growth hormones will be produced, due to which the plant will not grow much and remain a dwarf plant.

Page No 192:

Question 22:

(a) State one advantage of variation to a species.
(b) What are sex chromosomes? How many sex chromosomes are there? Name them.

Answer:

(a) The one advantage of variation to a species is that it increases the chances of the species' survival in a changing environment.

(b) The chromosomes that determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes, the X chromosome and the Y chromosome.

Page No 192:

Question 23:

Explain how, sex is determined in human babies.

Answer:

In humans, sex is determined at the time of fertilisation. If the father contributes X chromosome during fertilisation through his sperm, then the baby born will be a girl. On the other hand, if chromosome Y is contributed through his sperm, then the newborn will be a boy. 

Page No 192:

Question 24:

What do the following symbols used in the topic on heredity represent?
(a) TT
(b) tt
(c) XX
(d) XY

Answer:

(a) TT represents a tall plant.
(b) tt represents a dwarf plant.
(c) XX represents a female.
(d) XY represents a male.

Page No 192:

Question 25:

(a) What will you get in the F1 and F2 generations in the following cross?
Pure tall pea plant × Pure dwarf pea plant
(b) It it an example of monohybrid cross or dihybrid cross?

Answer:

(a) In the F1 generation, we will get all tall plants. In the F2 generation, we will get tall and dwarf plants in the ratio 3:1.
(b) It is an example of monohybrid cross, as only one character (i.e., plant height) is considered for crossing.

Page No 192:

Question 26:

In the F2 generation of a cross, progeny having different traits are produced in the ratio 3 : 1. State whether it is a monohybrid cross or a dihybrid cross? Give one example of such a cross.

Answer:

It is a monohybrid cross. When a tall pea plant (TT) is crossed with a dwarf pea plant (tt), then in the F1 generation, all tall pea plants (with genotype Tt) are obtained. If these tall plants (Tt) are self-crossed, then in the F2 generation, the tall and dwarf plants will be in the ratio 3:1.  

Page No 192:

Question 27:

(a) What is the genotype of dwarf plants which always produced dwarf offspring?
(b) What is the genotype of tall plants which always produced tall offspring?
(c) What is the genotype of (i) dwarf plants, and (ii) tall plants, whose parental cross always produces tall offspring?

Answer:

(a) tt is the genotype of dwarf plants which always produces a dwarf offspring.
(b) TT is the genotype of tall plants which always produces a tall offspring.
(c) (i) tt is the genotype of dwarf plants; and,
     (ii) TT is the genotype of tall plants. The parental cross of (ii) always produces a tall offspring.

Page No 192:

Question 28:

(a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (i) sperm cell, and (ii) zygote?
(b) What sizes of plants are produced if both parents have genes Tt?

Answer:

(a) (i) A sperm cell will have half the number of chromosomes than present in a normal cell. Hence, the number of chromosomes present in it will be 23.
      (ii) Number of chromosomes in a zygote will be same as present in a normal cell. Hence, the number of chromosomes present in it will be 46.

(b) Tall and dwarf plants will be produced in the ratio 3:1.

Page No 192:

Question 29:

In a human, how many chromosmes are present in :
(a) a brain cell?
(b) a sperm in the testes?
(c) an egg which has just been produced by the ovary?
(d) a skin cell?
(e) a fertilised egg?

Answer:

(a) In a brain cell in a human has 46 chromosomes.

(b) A sperm in the testes has 23 chromosomes.

(c) An egg which has just been produced by the ovary has 23 chromosomes.

(d) A skin cell has 46 chromosomes.

(e) A fertilised egg has 46 chromosomes.

Page No 192:

Question 30:

Gregor Mendel's first law of genetics states "Of a pair of contrasted characters, only one can be represented in a gamete by its internal 'factor'.
(a) Give the modern name for this 'factor'.
(b) State where these factors are found in gametes.

Answer:

(a) The modern name for this 'factor' is genes.
(b) These factors or genes are present on chromosomes in gametes.

Page No 192:

Question 31:

Does genetic combination of mother play a significant role in determining the sex of a new born baby?

Answer:

Genetic combination of mother does not play a significant role in determining the sex of a new born baby. Genetic combination of father decides the sex of the baby which the mother will give birth to.

Page No 192:

Question 32:

Give the contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive :
(a) Yellow seed
(b) Round seed

Answer:

(a) Green seed. Yellow seed is the dominant trait and green seed is the recessive trait.
(b) Wrinkled seed. Round seed is the dominant trait and wrinkled seed is the recessive trait.

Page No 192:

Question 33:

(a) What is meant by 'heredity'? What are the units of heredity.
(b) State Mendel's first law of inheritance.

Answer:

(a) The transmission of characters from the parents to their offsprings is called heredity. Genes are the units of heredity which transfer characteristics from parents to their offsprings during reproduction.

(b) Mendel's first law of inheritance states that the characteristics of an organism are determined by internal factors which occur in pairs. Only one of a pair of such factors can be present in a single gamete.



Page No 193:

Question 34:

(a) Why did Mendel choose pea plants for conducting his experiments on inheritance?
(b) State Mendel's second law of inheritance.

Answer:

(a) Mendel chose pea plants for studying inheritance because of the following reasons:

  • Pea plants had a number of clear cut differences which were easy to tell apart. For example, some pea plants were 'tall' whereas others were 'dwarf'.
  • They were self pollinating plants.
  • Many generations of pea plants can be produced in a comparatively short time span and their study is much simpler than that of animals.
(b) Mendel's second law of inheritance states that 'in the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair of traits are distributed independently to the gametes.'

Page No 193:

Question 35:

(a) What do you understand by the term 'variation'?
(b) Name two human traits which show variation.
(c) How does the creation of variation in a species ensure its survival?

Answer:

(a) The differences in the characters (or traits) among the individuals of a species is called variation.

(b) Human height and skin colour are two traits which show variation.

(c) The great advantage of variation to a species is that it increases their chances of survival in a changing environment. For example, the accumulation of heat resistant variation in some bacteria will ensure its survival even when the temperature in its environment rises too much, due to a heat wave or any other reason. On the other hand, the bacteria which did not have this variation to withstand heat would not survive under these circumstances, and die.

Page No 193:

Question 36:

(a) What are genes? Where are they located in our body?
(b) What is meant by dominant genes and recessive genes? Give one example of each.
(c) Explain how, characteristics (or traits) are inherited through genes.

Answer:

(a) Genes are units of heredity which transfer characteristics (or traits) from parents to their offsprings during reproduction. Genes are located on chromosomes.

(b) The gene which decides the appearance of an organism even in the presence of an alternative gene is known as dominant gene. The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. For example, in pea plants, the dominant gene for tallness is T and the recessive gene for dwarfism is t

(c) Genes are responsible for the characteristic features of an organism. The characteristics or traits of parents are transmitted to their progeny through genes present on their chromosomes during the process of sexual recombination. There is a pair of genes for each characteristic of an organism. However, each parent passes only one of the two genes of the pair for each characteristic to its progeny through gametes. Thus, the male gamete and female gamete carry one gene for each characteristic form the gene pairs of parents. But when a male gamete fuses with a female gamete during fertilisation, they make a new cell called zygot,e with a full set of genes. This zygote grows and develops to form a new organism having characteristics from both the parents.

Page No 193:

Question 37:

(a) How do Mendel's experiments show that traits may be dominant or recessive?
(b) How do Mendel's experiments show that traits are inherited independently?

Answer:

(a) Mendel crossed pure-bred tall pea plants with pure-bred dwarf pea plants and found that only tall pea plants were produced in the F1 generation. From this, Mendel concluded that the F1 generation showed the traits of only one of the parents: tallness. The trait of other parent plant, dwarfness, did not show in the progeny of the first generation. When tall pea plants of the first generation were crossed, then in F2 generation, tall plants and dwarf plants were obtained in the ratio 3:1.
From these experiments, Mendel concluded that the trait for dwarfness of one of the parent pea plant had not been lost. It was merely concealed or suppressed in the first generation to reemerge in the second generation.
 

(b) Mendel chose two contrasting characters: shape and colour of seeds. The pea plants had round-yellow seeds and wrinkled green seeds. Mendel first crossed pure-bred pea plants with round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the first generation. From this, he concluded that round shape and yellow colour of the seeds were dominant traits over the wrinkled shape and green colour of the seeds. When the F1 generation pea plants with round-yellow seeds were cross-bred by self pollination, then four types of seeds with different combinations of shape and colour were obtained in the F2 generation. Mendel observed that he had started with two combinations of characteristics in seeds and two new combinations of characteristics had appeared in the F2 generation i.e. round-green and wrinkled-yellow. On the basis of this observation, Mendel concluded that though the two pairs of original characteristics​ combine in the F1 generation, they separate and behave independently in subsequent generations.

Page No 193:

Question 38:

When two parents are crossed, the offspring are referred to as :
(a) recessives
(b) test cross
(c) F1 generation
(d) F2 generation

Answer:

(c) F1 generation
When two parents cross to produce progeny, their progeny is called first filial generation (or F1 generation).

Page No 193:

Question 39:

A cross between two individuals results in a ratio of 9 : 3 : 3 : 1 for four possible phenotypes of progeny. This is an example of a :
(a) dihybrid cross
(b) monohybrid cross
(c) test cross
(d) none of these

Answer:

(a) dihybrid cross
 A dihybrid cross gives progeny in the ratio of  9: 3: 3: 1.

Page No 193:

Question 40:

For his experiments on heredity, Mendel used :
(a) papaya plants
(b) potato plants
(c) pea plants
(d) pear plants

Answer:

(c) pea plants
 Mendel used pea plants for his experiments on heredity.

Page No 193:

Question 41:

The human animal which has an XY pair of chromosomes is called :
(a) male
(b) hybrid
(c) female
(d) doomed

Answer:

(a) male
 In humans, XY combination of chromosomes represents a male.

Page No 193:

Question 42:

The science of heredity is known as :
(a) biology
(b) embryology
(c) genetics
(d) biochemistry

Answer:

(c) genetics
The science of heredity is known as genetics.

Page No 193:

Question 43:

A gene is a :
(a) hybrid
(b) heritable trait
(c) pure breed
(d) part of a chromosome that transmits a trait

Answer:

(d) part of a chromosome that transmits a trait
A gene is a unit of heredity present on chromosomes that transfers characteristic from parents to their offsprings during reproduction.

Page No 193:

Question 44:

A normal cell of human body contains 23 pairs of chromosomes. The number of chromosomes  in a sex cell (sperm or ovum) of a human being is most likely to be :
(a) 46
(b) 23
(c) 21
(d) 42

Answer:

(b) 23
 The number of chromosomes present in a sex cell of a human being would normally be 23.

Page No 193:

Question 45:

In order to ensure that he had pure-breeding plants for his experiments, Mendel :
(a) cross-fertilised each variety with each other
(b) let each variety self fertilise for several generations
(c) removed the female parts of the plants
(d) removed the male parts of the plants.

Answer:

(b) let each variety self fertilise for several generations
Mendel ensured that he used pure breeding plants for his experiments by letting each variety self-pollinate for several generations.

Page No 193:

Question 46:

In the human blood grouping, the four basic blood types are type A, type B, type AB, and type O. The blood proteins A and B are :
(a) simple dominant and recessive traits
(b) incomplete dominant traits
(c) codominant traits
(d) sex-linked traits

Answer:

(c) codominant traits
 Blood proteins A and B are codominant traits, as neither of these is able to dominate the other completely.

Page No 193:

Question 47:

A plant with two 'small' genes breeds with a plant with two 'tall' genes to produce :
(a) small plants and tall plants in the ratio 1 : 3
(b) all small plants
(c) all tall plants
(d) tall plants and small plants in the ratio 3 : 1

Answer:

(c) all tall plants
 All tall plants will be produced because tall genes are dominant over small genes.

Page No 193:

Question 48:

A pregnant woman has an equal chance of her baby being blood group A or blood group AB. Which one of the following shows the possible genotypes of the woman and the father of her child?
(a) IA IA and IB IO
(b) IA IB and IB IO
(c) IA IO and IB IO
(d) IA IB and IA IO

Answer:

(a) IA IA and IB IO
Possible genotypes should be IAIA and IBIO because these two combinations will produce progeny either with blood group A or blood group AB.

Page No 193:

Question 49:

The palisade cells of a species of plant contain 28 chromosomes. How many chromosomes will there be in each gamete produced by the plant?
(a) 56
(b) 28
(c) 14
(d) 4

Answer:

(c) 14
Palisade cells of leaves are somatic cells. Each gamete produced by the plant will have half the number of chromosomes present in a palisade cell i.e. 14 chromosomes.

Page No 193:

Question 50:

Which of the following may be used to obtain an F2 generation?
(a) allowing flowers on a parent plant to be self-pollinated
(b) allowing flowers on an F1 plant to be self-pollinated
(c) cross-pollinating an F1 plant with a parent plant
(d) cross-pollinating two parent plants

Answer:

(a) allowing flowers on a parent plant to be self-pollinated
    F2 generation can be obtained by allowing flowers on the plants of F1generation to be self-pollinated.



Page No 194:

Question 51:

The following results were obtained by a scientist who crossed the F1 generation of pure-breeding parents for round and wrinkled seeds.

Dominant trait Recessive trait No. of F2 offspring
Round seeds Wrinkled seeds 7524
From these results, it can be concluded that the actual number of round seeds he obtained was:
(a) 1881
(b) 22572
(c) 2508
(d) 5643

Answer:

(d) 5643
The round and wrinkled seeds will be obtained in the ratio 3:1. 
Number of round seeds obtained will be =7524 ×34 = 5643
​

Page No 194:

Question 52:

The visible characteristic in an organism is known as :
(a) prototype
(b) stereotype
(c) phenotype
(d) genotype

Answer:

(c) phenotype
The characteristic (or trait) in an organism that is visible is called its phenotype.

Page No 194:

Question 53:

The exchange of genetic material takes place in :
(a) vegetative reproduction
(b) asexual reproduction
(c) sexual reproduction
(d) budding

Answer:

(c) sexual reproduction
The exchange of genetic material occurs during meiosis, that takes place in the gametes of sexually reproducing organisms.

Page No 194:

Question 54:

A cross between a tall plant (TT) and short plant (tt) resulted in progeny that were all tall plants because :
(a) tallness is the dominant trait
(b) shortness is the dominant trait
(c) tallness is the recessive trait
(d) height of plant is not governed by gene T or t

Answer:

(a) tallness is the dominant trait
  In progeny, all plants obtained will be tall because tallness is the dominant trait, while dwarfism is the recessive trait.

Page No 194:

Question 55:

The number of pair(s) of sex chromosomes in the zygote of humans is :
(a) one
(b) two
(c) three
(d) four

Answer:

(b) two
The number of sex chromosomes in the zygote of humans is two-- XX in females and XY in males.

Page No 194:

Question 56:

In peas, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plants to pure short plants in F2 generation will be :
(a) 1 : 3
(b) 3 : 1
(c) 1 : 1
(d) 2 : 1

Answer:

(c) 1 : 1
    The ratio of pure tall plants to pure short plants in F2 generation will be 1:1. The other two plants produced will also     be tall, but they will not be pure.

Page No 194:

Question 57:

The two versions of a trait (character) which are brought in by the male and female gametes are situated on :
(a) copies of the same chromosome
(b) sex chromosomes
(c) two different chromosomes
(d) any chromosomes

Answer:

(a) copies of the same chromosome
The two versions of a trait, which are brought in by the female and male gametes are situated on the copies of the same chromosome.

Page No 194:

Question 58:

Select the statements that describe characteristics of genes :
(i) genes are specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene

(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Answer:

(b) (i) and (iii)
A gene is the section in a DNA on a chromosome that codes for the formation of a protein, controlling a specific characteristic of the organism. The two genes which are responsible for a particular characteristic are always present on the corresponding position of the pair of chromosomes. There are thousands of genes on a chromosome, which control various characteristics of an organism.

Page No 194:

Question 59:

Select the group which shares the maximum number of common characters :
(a) two individuals of a species
(b) two species of a genus
(c) two genera of a family
(d) two genera of two families

Answer:

(a) two individuals of a species
 Two individuals of a species share the maximum number of common characters.

Page No 194:

Question 60:

A trait in an organism is influenced by :
(a) paternal DNA only
(b) maternal DNA only
(c) both maternal and paternal DNA
(d) neither by paternal nor by maternal DNA.

Answer:

(c) both maternal and paternal DNA
  A trait in an organism is influenced by both maternal and paternal DNA. This is because in zygote, one half of the   chromosomes is contributed by the mother, and the other half by the father.

Page No 194:

Question 61:

In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosomes is/are :
(i) large chromosome
(ii) small chromosome
(iii) Y chromosome
(iv) X chromosome

(a) (i) and (ii)
(b) (iii) only
(c) (iii) and (iv)
(d) (ii) and (iv)

Answer:

(c) (iii) and (iv)
In human males, the X and Y chromosomes remain unpaired during meiosis.

Page No 194:

Question 62:

The sex of a child is determined by which of the following?
(a) the length of the mother's pregnancy
(b) the length of time between ovulation and copulation
(c) the presence of and X chromosome in an ovum
(d) the presence of a Y chromosome in a sperm

Answer:

(d) the presence of a Y chromosome in a sperm
  The sex of a child is determined by the Y chromosome that is present in a sperm.

Page No 194:

Question 63:

A zygote which has inherited an X chromosome from the father will develop into :
(a) baby boy
(b) baby girl
(c) adult
(d) either boy or girl

Answer:

(b) baby girl
  A zygote which has inherited an X chromosome from the father will develop into a baby girl. The combination XX of   sex chromosomes tends to develop into females.

Page No 194:

Question 64:

Which of the following statement is incorrect?
(a) for every hormone there is a gene
(b) for every protein there is a gene
(c) for production of every enzyme there is a gene
(d) for every type of fat there is a gene

Answer:

(d) for every type of fat there is a gene
      Fats are not synthesised by genes present on chromosomes.



Page No 195:

Question 65:

If the ratio of each phenotype of the seeds of pea plants in the F2 generation is 9 : 3 : 3 : 1, it is known as :
(a) tetrahybrid ratio
(b) monohybrid ratio
(c) dihybrid ratio
(d) trihybrid ratio

Answer:

(c) dihybrid ratio
    The ratio 9: 3: 3: 1 is known as the dihybrid ratio.

Page No 195:

Question 66:

In humans, if gene B gives brown eyes and gene b gives blue eyes. What will be the colour of eyes of the persons having the following combination of genes?
(a) Bb
(b) bb
(c) BB

Answer:

(a) Combination Bb will give brown eyes.
(b) Combination bb will give blue eyes.
(c) Combination BB will give brown eyes.

Page No 195:

Question 67:

Pure-bred pea plants A are crossed with pure-bred pea plants B. It is found that the plants which look like A do not appear in F1 generation but re-emerge in F2 generation. Which of the plants A and B are : (i) tall, and (ii) dwarf? Give reason for your answer.

Answer:

(i) Pea plants B are the tall ones. It is because these plants carry the trait for tallness, which is dominant.

(ii) Pea plants A are dwarfs. It is because these plants carry the trait for dwarfism, which is recessive. A recessive           trait remains hidden in F1 generation but reappears in F2 generation.

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Question 68:

Pure-bred tall pea plants are first crossed with pure-bred dwarf pea plants. The pea plants obtained in F1 generation are then cross-bred to produce F2 generation of pea plants.
(a) What do the plants of F1 generation look like?
(b) What is the ratio of tall plants to dwarf plants in F2 generation?
(c) Which type of plants were missing in F1 generation but reappeared in F2 generation?

Answer:

(a) All plants in F1 generation will be tall.
(b) In F2 generation, the ratio of tall plants to dwarf plants will be 3:1.
(c) Dwarf pea plants were missing in F1 generation, but reappeared in F2 generation.

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Question 69:

A plant has two varieties, one with red petals and the other with white petals. When these two varieties are cross-pollinated, all the offsprings have red petals?
(a) Which gene is dominant?
(b) Choose suitable letters to represent the two genes.

Answer:

(a) The gene for red petals is dominant, while the gene for white petals is recessive.
(b) The gene for red petals can be represented by R and the gene for white petals can be represented by r.

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Question 70:

A red-haired woman marries a brown-haired man, and all the children are brown haired. Explain this genetically.

Answer:

Brown coloured hair is dominant over red. Hence, when a red-haired woman marries a brown-haired man, all their children are brown haired.

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Question 71:

A black mouse mates with a brown mouse, and all the offsprings are black.
(a) Why are no brown offsprings produced?
(b) If two of the black offsprings mate with each other what kind of offspring would you expect and in what proportions? Give reason for your answer.

Answer:

(a) No brown offsprings are produced because brown colour is recessive, while black is dominant. The recessive trait does not occur in F1 generation.
(b) We would expect black and brown offsprings in the ratio 3:1. It is because brown colour reappears in F2 generation.

Page No 195:

Question 72:

(a) E is the gene for brown eye colour and and e is the gene for blue eye colour. which gene is (i) recessive, and (ii) dominant?
(b) Both father and mother have the genes Ee in their cells. What colour are their eyes?
(c) Which combination of genes in the zygote will produce children with blue eyes?
(d) Which combination of genes in the zygote will produce children with brown eyes?

Answer:

(a) (i) e is recessive; (ii) E is dominant
(b) The colour of their eyes is brown.
(c) Combination ee will produce children with blue eyes.
(d) Combination EE or Ee will produce children with brown eyes.

Page No 195:

Question 73:

What are the possible blood groups likely to be inherited by children born to a group A mother and a group B father? Explain your reasoning.

Answer:

The mother with blood group A has genotype IAIO. The father with blood group B has genotype IBIO. Hence ,the possible genotypes of the children will be IAIB, IAIO, IBIOand IOIO. Thus, the possible blood groups of the children will be AB, A, B and O.

Page No 195:

Question 74:

A couple with a newborn baby is troubled that the child does not resemble either of them. Suspecting that a mixup occurred at the hospital, they check the blood type of the infant. It is type O. Because the father is type A and the mother type B, they conclude that a mixup has definitely occurred. Are they correct? Give reason for your answer.

Answer:

They are not correct. The father with blood group A has genotype IAIO. The mother with blood group B has genotype IBIO. Hence, the possible genotypes of the children will be IAIB, IAIO, IBIO  and IOIO. Thus, the possible blood groups of children will be AB, A, B and O. Hence, if the father has blood group A, and the mother has blood group B, it is possible for them to have children with blood group O.

Page No 195:

Question 75:

A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits-blood group A or O - is dominant? Why or why not?

Answer:

No. There are two possibilities:
Case I: If the father's blood group is A, and is the dominant trait, his genotypes will be IAIA and IAIO ; and the mother's blood group O being a recessive trait, her genotype will be IOIO​. So, the daughter can receive one recessive allele IO from the father and another from the mother to have genotype IOIO and the blood group O.
Case II: If the father's blood group A is a recessive trait, his genotype will be IAIA ; the mother's blood group O being a dominant trait, her genotype will be IOIO​ and IOIA. So, the daughter can receive one dominant allele IO from the mother and one recessive allele IA from the father to have genotype IOIA and blood group O.

Page No 195:

Question 76:

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggested that the genetic make up (or genotype) of the tall parent can be depicted as :
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Give reason for your choice.

Answer:

(c) TtWW
    The genotype of the tall parent can be depicted as TtWW. It is because T is the gene for tallness, t for dwarfness;     â€‹W is the gene for violet flowers, while w is for white flowers. Thus, T and W are dominant genes, whereas t and w     are recessive genes.

Page No 195:

Question 77:

A person first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only A-B type of seeds were produced in the F1 generation. When F1 generation pea plants having A-B type of seeds were cross-bred by self-pollination, then in addition to the original round-yellow and wrinkled-green seeds, two new varieties A-D and C-B type of seeds were also obtained.
(a) What are A-B type of seeds?
(b) State whether A and B are dominant traits or recessive traits.
(c) What are A-D type of seeds?
(d) What are C-B type of seeds?
(c) Out of A-B and A-D types of seeds, which one will be produced in (i) minimum numbers, and (ii) maximum numbers, in the F2 generation?

Answer:

(a) A-B type of seeds are round-yellow.
(b) A (round) and B (yellow) are dominant traits.
(c) A-D type of seeds are round-green.
(d) C-B type of seeds are wrinkled-yellow.
(e) In the F2 generations, (i) A-D type seeds will be produced in minimum numbers; (ii) A-B type of seeds will be       produced in maximum numbers.



Page No 196:

Question 78:

The person A has only B chromosomes in all its gametes. On the other hand, another person C has chromosome D in half of gametes and chromosome E in the other half of gametes. When chromosomes B and D combine during fertilisation, a female zygote results. On the other hand, combination of B and E chromosomes produces a male zygote.
(a) What are chromosomes (i) B (ii) D, and (iii) E?
(b) Out of B, D and E, which two chromosomes are of the same type?
(c) Which chromosome is smaller in size?
(d) What is the general name of chromosomes such as B and E?
(e) Out of the two persons A and C, which one is (i) male, and (ii) female?

Answer:

(a) (i) B is X chromosome; (ii) D is also X chromosome; (iii) E is Y  chromosome.
(b) Chromosomes B and D are of same type.
(c) Chromosome E is smaller in size.
(d) Chromosomes B and E are called sex chromosomes.
(e) (i) A is female; (ii) C is male.

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Question 79:

Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the F1 generation. When F1 generation pea plants having round-yellow seeds were cross-bred by self pollination, then peas having round-yellow seeds, round green seeds, wrinkled-yellow seeds and wrinkled-green seeds were produced. Mendel collected a total of 2160 seeds.
(a) What will be the number of (i) round green seeds (ii) wrinkled green seeds (iii) round yellow seeds, and (iv) wrinkled-yellow seeds?
(b) Which 'ratio' as established by Mendel have you made use of in answering the part (a) above?

Answer:

(a) 
 (i)Number of round green seeds = 216016×3 =405(ii)Number of wrinkled green seeds = 216016×1 =135(iii)Number of round yellow seeds = 216016×9 =1215(iv)Number of wrinkled yellow seeds = 216016×3 =405

(b) The dihybrid ratio (which is 9: 3: 3: 1) has been used to answer part (a).

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Question 80:

Pure-bred round-yellow pea seeds have genotype RRYY and the pure-bred wrinkled-green pea seeds have genotype rryy. Keeping this in mind, write the phenotypes of the following genotypes of hybrid pea seeds :
(a) Rryy
(b) rrYy
(c) rrYY
(d) RrYy
(e) RRyy


 

Answer:

(a) Round-green
(b) Wrinkled-yellow
(c) Wrinkled-yellow
(d) Round-yellow
(e) Round-green



Page No 208:

Question 1:

What name is given to the sequence of gradual changes over millions of years in which new species are produced?

Answer:

The sequence of gradual changes which take place in primitive organisms over millions of years, in which new species are produced is called speciation.

Page No 208:

Question 2:

Name the scientist who gave the theory of evolution.

Answer:

It was Charles Robert Darwin who gave the theory of evolution.

Page No 208:

Question 3:

State whether the following statement is true or false :
Human beings have evolved from chimpanzees.

Answer:

False. Both chimpanzees and human beings evolved from a common ancestor long ago.

Page No 208:

Question 4:

State one characteristic which shows that the birds are very closely related to dinosaurs.

Answer:

The presence of feathers on birds indicates that they are very closely related to dinosaurs. This is because like birds, even dinosaurs had feathers, though they could not fly using their feathers. 

Page No 208:

Question 5:

Name an animal having rudimentary eyes.

Answer:

Flatworms (Planaria) have rudimentary eyes.

Page No 208:

Question 6:

Name the ancestor of the following :
Broccoli, Kohlrabi, Kale

Answer:

Wild cabbage is the common ancestor of broccoli, kohlrabi and kale.

Page No 208:

Question 7:

Where did life originate on the earth?

Answer:

Life on earth originated in sea water.



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Question 17:

Match the terms given in column I with those given in column II :

Column I   Column II
(i) Fossil   (a) A famous evolutionist
(ii) A theory of evolution   (b) Survival of the fittest
(iii) Probable ancestor of birds   (c) Petrified remains of prehistoric life
(iv) Charles Darwin   (d) Father of genetics
(v) Gregor Mendel   (e) Archaeopteryx

Answer:

      Column I                                    Column II
(i) Fossil                                           (c) Petrified remains of prehistoric life
(ii) A theory of evolution                    (b) Survival of the fittest    
(iii) Probable ancestor of birds            (e) Archaeopteryx
(iv) Charles Darwin                           (a) A famous evolutionist
(v) Gregor Mendel                             (d) Father of genetics

Page No 209:

Question 18:

What is meant by acquired and inherited traits? Explain with one example each.

Answer:

The traits of an organism that are not inherited, but develop in response to the environment, are called acquired traits. For example, if a mouse's tail gets cut, the cut tail is an acquired trait.
The trait of an organism that is caused by a change in its genes is called an inherited trait. Inherited traits can be passed on to the progeny of the organism. For example, eye colour in humans is an inherited trait. 

Page No 209:

Question 19:

Why are the traits acquired during the lifetime of an individual not inherited?

Answer:

Traits acquired during the lifetime of an individual are not inherited, as these traits develop in the individual in response to the environment. Only those traits  which are associated with the DNA of the parents are passed onto children. Acquired traits do not make any changes in the DNA; hence, they are not passed from parents to children.

Page No 209:

Question 20:

Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer:

The wings of butterflies and bats cannot be considered homologous organs, as their basic designs are different.

Page No 209:

Question 21:

Name two animals having homologous organs and two having analogous organs. Name these organs.

Answer:

Lizards and frogs have homologous organs; their forelimbs are homologous.
Insects and birds have analogous organs; their wings are analogous. 

Page No 209:

Question 22:

What are fossils? Giving one example, explain how fossils provide evidence for evolution.

Answer:

The remains of animals or plants that lived in the past are known as fossils. The fossil bird Archaeopteryx looks like a bird, but it has many other features that are also present in reptiles. This is because Archaeopteryx had feathered wings like those of birds, but teeth and tail like those of reptiles. Thus, the study of fossils provide evidence for evolution.

Page No 209:

Question 23:

Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer:

(i) The study of fossils provide direct evidence of evolutionary relationship among species. For example, dinosaurs had   feathers, as fossils indicate. However, they could not fly. Later on, birds adapted the feathers to use them for flight.   This means that birds are very closely related to reptiles as dinosaurs were reptiles.

(ii) Another method is of comparison of the DNA of different species. The more closely the DNAs of two species are   â€‹related, the more common evolutionary history these species have.

Page No 209:

Question 24:

In what way are homologous organs evidence for evolution?

Answer:

Homologous organs are those organs which have same basic structure, but perform different functions. For example, the forelimbs of humans, cheetahs, whales and bats have the same basic structure. But humans use forelimbs for grasping, cheetahs for running, whales for swimming and bats for flying. The presence of homologous organs indicate that all these forelimbs have evolved from a common ancestral animal which had a 'basic design' of limb. 

Page No 209:

Question 25:

Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer:

The small numbers of surviving tigers is a cause for worry from the point of view of genetics, because if all tigers perish and become extinct, their genes will be lost forever.

Page No 209:

Question 26:

Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Give reason for your answer.

Answer:

Geographical isolation cannot be a major factor in the speciation of an asexually reproducing organism, as it does not require the aid of any other organism to carry out reproduction. 

Page No 209:

Question 27:

Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.

Answer:

The various tools of tracing evolutionary relationships that have been used for studying human evolution are: excavation, carbon-dating, study of fossils and determination of DNA sequences.

Page No 209:

Question 28:

Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms? Give reason for your answer.

Answer:

Spiders, fish and chimpanzee have a better body design compared to bacteria, as they can adapt to the changes in the environment in a better way, due to their complex body structure; that increases their chances of survival. 

Page No 209:

Question 29:

With the help of an example, explain how variation leads to evolution.

Answer:

Variations which are beneficial to the organism is passed on to its progeny, leading to evolution of species. For example, the green colour of a beetle is an inherited trait, that helps in its survival (as it can by mix with green bushes to hide). It is a beneficial variation and is brought about by a change in the genes of the reproductive cells.  

Page No 209:

Question 30:

(a) What is meant by a species? Give two examples of plant species and two of animals.
(b) State the various factors which could lead to the formation of new species.

Answer:

(a) A species is a population of organisms consisting of similar individuals which can breed together and produce fertile     offspring. Wheat and paddy are examples of plant species. Humans and cats are examples of animal species.

(b) The important factors which could lead to the formation of new species are:
    (i) Geographical isolation of a population caused by various types of barriers
    (ii) Genetic drift caused by drastic changes in the frequencies of particular genes, by chance alone
    (iii) Variations caused in individuals due to natural selection.

Page No 209:

Question 31:

What evidence do we have for the origin of life from inanimate matter (lifeless matter)?

Answer:

The experiments conducted by Stanley L. Miller and Harold C. Urey provided the evidence that the life originated from inanimate matter, like inorganic molecules.

Page No 209:

Question 32:

Does geographical isolation of individuals of a species lead to the formation of a new species? Provide a suitable explanation for your answer.

Answer:

Geographical isolation of individuals of a species leads to the formation of a new species, as it interrupts the flow of genes between their isolated populations through the gametes. 

Page No 209:

Question 8:

Write the names of at least three inorganic molecules which helped in the origin of life on the earth.

Answer:

Methane, ammonia and hydrogen sulphide are three inorganic molecules, which helped in the origin of life on the earth.

Page No 209:

Question 9:

Name the famous book written by Charles Robert Darwin.

Answer:

The famous book written by Charles Robert Darwin is The Origin of Species.

Page No 209:

Question 10:

The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs?

Answer:

The forelimbs of a frog, a bird and a man have the same basic design, but they perform different functions. Organs such as these are called homologous organs.

Page No 209:

Question 11:

Name two organisms which are now extinct and studied from their fossils.

Answer:

Trilobites (marine arthropods) and dinosaurs are now extinct and are studied from their fossils.

Page No 209:

Question 12:

Out of the wing of a bird, wing of an insect and the wing of a bat :
(a) which two are homologous organs?
(b) which two are analogous organs?

Answer:

(a) The wings of birds and bats are homologous organs, as despite the fact that they have the same basic structure,          they perform different functions. 
(b) Wings of birds and insects are analogous organs, as their basic structures are different, but they perform the same      function (i.e., flying).

Page No 209:

Question 13:

Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer:

It is because human beings, despite these differences, can interbreed to produce fertile offsprings.

Page No 209:

Question 14:

 Name five varieties of vegetables which have been produced from 'wild cabbage' by the process of artificial selection.

Answer:

Broccoli, cabbage, cauliflower, kohlrabi and kale are five varieties of vegetables, which have been produced from 'wild cabbage' by the process of artificial selection.

Page No 209:

Question 15:

Choose the one term from the following which includes the other three :
broccoli, wild cabbage, cauliflower, cabbage

Answer:

Wild cabbage includes the other vegetables: broccoli, cauliflower and cabbage. These three have evolved from wild cabbage by the process of artificial selection.

Page No 209:

Question 16:

Fill in the following blanks with suitable words :
(a) The human forelimb and bat's forelimb are an example of .......... organs whereas an insect's wing and a bat's wing are an example of ........... organs.
(b) The evolution of eye is an example of evolution by ............
(c) The scientific name of all human beings is ..............
(d) Broccoli has evolved from .............. by the process of artificial selection.
(e) The theory of natural selection for evolution was proposed by ..............

Answer:

(a) The human forelimb and a bat's forelimb are an example of homologous organs, whereas an insect's wing and a bat's wing are an example of analogous organs.
(b) The evolution of the eye is an example of evolution by stages.
(c) The scientific name of all human beings is Homo sapiens.
(d) Broccoli was developed from wild cabbage by the process of artificial selection.
(e) The theory of natural selection for evolution was proposed by Charles Darwin.



Page No 210:

Question 33:

Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Explain your answer.

Answer:

Despite the fact that humans have a more complex body plan than bacteria, it does not mean that they are more evolved than bacteria. Bacteria still inhabit some of the most inhospitable habitats such as hot springs, deep-sea thermal vents and ice in Antarctica. Most other organisms cannot survive in such harsh environments. 

Page No 210:

Question 34:

(a) Name the scientist who gave the theory of origin of life on earth. What is this theory?
(b) How are those species which are now 'extinct' studied?

Answer:

(a) The theory of origin of life on earth was given by J.B.S. Haldane in 1929. He suggested that life must have evolved from the simple inorganic molecules such as ammonia, methane and hydrogen sulphide that were present on earth when it was formed. He said that conditions on earth at that time could have converted simple inorganic molecules into complex organic molecules necessary for life. These complex organic molecules must have combined together to form the first living organisms.

(b) The species that are extinct are studied through their fossils that are found by digging the earth. Carbon-dating method is used to find the age of a fossil.

Page No 210:

Question 35:

What do you understand by the term 'evolution'? State Darwin's theory of evolution.

Answer:

Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years, during which new species are produced. 

Darwin's theory of evolution:
(a) Within any population, there is natural selection. Some individuals have more favourable variations than others. 
(b) Even though all species produce a large number of offsprings, population remains fairly constant naturally.
(c) This is due to the struggle between members of the same species and different species for food, space and mate.
(d) the struggle within populations eliminates the unfit individuals. The fit individuals possessing favourable variations   survive and reproduce. This is called natural selection.
(e) The individuals having favourable variations pass on these variations to their progeny from generation to   generation.
(f) These variations when accumulated over a long period of time lead to the origin of new species.

Page No 210:

Question 36:

(a) Explain the terms 'analogous organs' and 'homologous organs' with examples.
(b) In what way are analogous organs evidence for evolution?

Answer:

(a) Analogous organs are those organs which have different basic structure, but perform the same function. For example, the wing of an insect and a bird have completely different basic structure, but they perform the same functionof flying.  
Homologous organs are those organs which have same basic structure but perform different functions. For example, the forelimbs of humans, cheetahs, whales and bats have the same basic structural plan. But the forelimbs in humans are used for grasping, in cheetah for running, in whales for swimming and in bats for flying. 

(b)  The presence of analogous organs in different animals provide evidence for evolution by telling us that though they are not derived from common ancestors, they can still evolve to perform similar functions to survive, flourish and keep on evolving in the prevalent environment. Thus, the presence of analogous organs provide a mechanism for evolution.  

Page No 210:

Question 37:

(a) Define 'speciation'. Explain how speciation occurs.
(b) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Give reason for your answer.

Answer:

(a) The process by which new species develop from the existing ones is known as speciation. Speciation occurs when the population of the same species splits into two separate groups, which then get isolated from each other geographically by barriers such as mountain ranges, rivers or the sea. The geographical isolation of the two groups of population lead to their reproductive isolation due to which no genes are exchanged between them. However, breeding continues within the isolated populations producing more and more generations. Over the generations, the processes of genetic drift and natural selection operate in different ways in the two isolated groups of population and make them more and more different from each other. After thousands of years, the individuals of these isolated groups of population become so different that they will be incapable of reproducing with each other, even if they happen to meet again. In this way, two new species have been formed.

(b) Geographical isolation cannot be a major factor in the speciation of self-pollinating plant species, as it does not have to look to other plants for its process of reproduction to be carried out.

Page No 210:

Question 38:

(a) Define 'natural selection'.
(b) "Only variations that confer an advantage to an individual organism will survive in a population". Do you agree with this statement? Give reason for your answer.

Answer:

(a) Natural selection is the process of evolution of a species in which characteristics that help individual organisms to survive and reproduce are passed on to their offsprings and those characteristics which do not help are not passed.

(b) Yes, we agree with the statement. Some changes always appear when animals produce their progeny by sexual reproduction. One of the progeny may be taller than the other. The advantage of long legs to the progeny is that when no food is available on the ground, those with long legs can reach the leaves on tall trees, eat them and survive. On the other hand, the progeny that are short cannot reach the leaves on tall trees. They will not get any food and eventually die from starvation. Now, since long legs are a beneficial variation, the long-legged animals will live long enough to produce their offsprings. So, all the future generations will be long-legged.

Page No 210:

Question 39:

In evolutionary terms, we have more in common with :
(a) a chinese school boy
(b) a chimpanzee
(c) a spider
(d) a bacterium

Answer:

(b) a chimpanzee
  In evolutionary terms, we have more in common with a chimpanzee because both human beings and chimpanzees   had a common ancestor, long time ago.

Page No 210:

Question 40:

The human species has genetic roots in :
(a) America
(b) Africa
(c) Australia
(d) Antarctica

Answer:

(b) Africa
    Earliest members of the human species came from Africa.

Page No 210:

Question 41:

Which of the following gas was not present in early earth atmosphere?
(a) Ammonia
(b) Oxygen
(c) Hydrogen sulphide
(d) Methane

Answer:

(b) Oxygen
    Oxygen was absent in early earth atmosphere.

Page No 210:

Question 42:

A gradual change, over a long period, in a form of life is known as :
(a) erosion
(b) evolution
(c) revolution
(d) evaluation

Answer:

(b) evolution
  Evolution is the sequence of gradual changes, which take place in primitive organisms over millions of years, due to   which new species are formed.

Page No 210:

Question 43:

Scientists believe that all life originated in :
(a) the sea
(b) the soil
(c) the ground
(d) the air

Answer:

(a) the sea
  Scientists believe that all life originated in sea water.

Page No 210:

Question 44:

According to scientists, aves have evolved from :
(a) mammals
(b) amphibians
(c) reptiles
(d) arthropods

Answer:

(c) reptiles
    According to scientists, aves have evolved from reptiles.

Page No 210:

Question 45:

The theory of evolution of species by natural selection was given by :
(a) Mendel
(b) Darwin
(c) Dalton
(d) Lamarck

Answer:

(b) Darwin
The theory of evolution of species by natural selection was given by Charles Darwin in his book The Origin of Species.

Page No 210:

Question 46:

The term 'father of genetics' is used for the scientist :
(a) Morgan
(b) Mendel
(c) Darwin
(d) Marie Curie

Answer:

(b) Mendel
  Mendel is known as the 'father of genetics'.

Page No 210:

Question 47:

One of the following traits cannot be inherited. This one is :
(a) colour of eyes
(b) colour of skin
(c) size of body
(d) nature of hair

Answer:

(c) size of body
    Body size is an acquired trait, and cannot be passed on to the progeny.

Page No 210:

Question 48:

Only one of the following characteristic of the parents can be inherited by their children. This one is :
(a) deep scar on chin
(b) snub nose
(c) technique of swimming
(d) cut nose

Answer:

(b) snub nose
  Snub nose is an inherited trait, and can be can be passed on to the progeny.

Page No 210:

Question 49:

The organs which perform different functions but have the same basic structure are known as :
(a) homologous organs
(b) analogous organs
(c) homolytic organs
(d) analytic organs

Answer:

(a) homologous organs
The organs that perform different functions but have the same basic structure are known as homologous organs. For example, forelimbs of humans and lizards are homologous.

Page No 210:

Question 50:

The organs which perform similar functions but have different basic structure are called :
(a) asymmetric organs
(b) analogous organs
(c) homologous organs
(d) homophonic organs

Answer:

(b) analogous organs
The organs which perform a similar function, but have different basic structures are called analogous organs. For example, wings of insects and birds are analogous.

Page No 210:

Question 51:

Wing of an insect and forelimb of a bird are :
(a) analogous organs
(b) analeptic organs
(c) homologous
(d) homophobic organs

Answer:

(a) analogous organs
Wings of an insect and forelimbs of a bird are analogous organs, as they have different structures but perform the same function of flying.

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Question 52:

If the fossil of an organism is found in the deeper layers of earth, then we can predict that :
(a) the extinction of organism has occurred recently
(b) the extinction of organism has occurred thousands of years ago
(c) the fossil position in the layers of earth is not related to its time of extinction
(d) time of extinction cannot be determined.

Answer:

(b) the extinction of organism has occurred thousands of years ago
Fossils found in the deepest layers of earth are the oldest ones. From these, scientists conclude that the extinction of an organism has occurred thousands of years ago.

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Question 53:

Which of the following statement is incorrect with respect to variations?
(a) all variations in a species have equal chance of survival
(b) change in genetic composition results in variations
(c) selection of variations by environmental factors forms the basis of evolutionary process
(d) variations are the minimum in asexual reproduction

Answer:

(a) all variations in a species have an equal chance of survival
  All variations in a species do not have an equal chance of survival. Variations may either be beneficial or harmful to the species.



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Question 54:

One of the following traits of the parents cannot be passed on to their future generations. This trait is :
(a) cleft chin
(b) pointed chin
(c) scarred chin
(d) broad chin

Answer:

(c) scarred chin
  Scarred chin is an acquired trait, which an individual gets due to an accident. It cannot be passed on to the progeny.

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Question 55:

Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution, this means that :
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structures in both the organisms
(d) birds have evolved from reptiles

Answer:

(d) birds have evolved from reptiles
    In the context of evolution, it means that birds have evolved from reptiles.

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Question 56:

Select the incorrect statement from the following :
(a) frequency of certain genes in a population changes over several generations resulting in evolution
(b) reduction in the weight of an organism due to starvation is genetically controlled
(c) low weight parents can have heavy weight progeny
(d) traits which are not inherited over generations do not cause evolution.

Answer:

(b) reduction in the weight of an organism due to starvation is genetically controlled
Reduction in the weight of an organism due to starvation occurs due to scarcity of food in the environment. It is not genetically controlled.

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Question 57:

New species may be formed if :
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place

(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)

Answer:

(a) (i) and (ii)
New species may be formed if DNA undergoes significant changes in germ cells and chromosome number changes in the gamete.

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Question 58:

According to the evolutionary theory, formation of a new species is generally due to :
(a) sudden creation by nature
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) movement of individuals from one habitat to another.

Answer:

(b) accumulation of variations over several generations
According to Darwin's theory of evolution, variations, when accumulated over a long period of time lead to the origin of a new species.

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Question 59:

The presence of which of the following types of organs in two animals indicates that they are not derived from a common ancestor?
(a) homologous organs
(b) excretory organs
(c) analogous organs
(d) reproductive organs

Answer:

(c) analogous organs
  Analogous organs have a different basic design, so they indicate that the animals are not derived from a common   ancestor.

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Question 60:

The presence of which of the following types of organs in two organisms indicates that they are derived from the same ancestor?
(a) analogous organs
(b) respiratory organs
(c) digestive organs
(d) homologous organs

Answer:

(d) homologous organs
  The presence of homologous organs indicates that the two organisms are derived from the same ancestor.

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Question 61:

One of the following has not been produced from wild cabbage by the process of artificial selection. This one is :
(a) kohlrabi
(b) cabbage
(c) spinach
(d) kale

Answer:

(c) spinach
  Spinach has not been produced from wild cabbage by the process of artificial selection.

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Question 62:

The fossil trilobite was originally :
(a) an arthropod
(b) an invertebrate
(c) a reptile
(d) an ave

Answer:

(a) an arthropod
Trilobites were marine arthropods which were common 400600 millions years ago.

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Question 63:

One pair of organs in the following animals are not homologous. This is :
(a) forelimbs in humans and lizard
(b) forelimbs in lizard and frog
(c) wings in butterfly and bat
(d) wings in bat and bird

Answer:

(c) wings in butterfly and bat
  Butterfly and bat wings cannot be considered homologous organs as they have different basic designs.

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Question 64:

The wings of a housefly and the wings of a sparrow are an example of :
(a) analogous organs
(b) vestigial organs
(c) respiratory organs
(d) homologous organs

Answer:

(a) analogous organs
The wings of a housefly and that of a sparrow are an example of analogous organs, as their basic structure is different,   but they are used for the same purpose; i.e., flying.

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Question 65:

Some of the important fossils which have been studied are those of organisms X, Y and Z. X were marine arthropods which were common between 400 to 600 million years ago. Y were the invertebrate animals (molluscs) with a flat, coiled, spiral shell which lived in the sea about 180 million years ago. Z are the extinct carnivorous or herbivorous reptiles which appeared on the earth about 250 million years ago and became extinct about 65 million years ago. What are X, Y and Z?

Answer:

X are trilobites, Y are ammonites and Z are dinosaurs.



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Question 66:

The farmers have been cultivating a food plant X for over two thousand years and have produced as many as five entirely different looking vegetables A, B, C, D and E from it.
(a) What could the plant X be?
(b) What are A, B, C, D and E?
(c) What is the process of evolution involved in this example known as?

Answer:

(a) X is wild cabbage.
(b) A is cabbage, B is broccoli, C is cauliflower, D is kohlrabi, E is kale.
(c) The process of artificial selection is involved in this example.

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Question 67:

There are five animals A, B, C, D and E. The animal A uses its modified forelimbs for flying. The animal B uses its forelimbs for running whereas the animal C uses its forelimbs for grasping. The animal D can live on land as well as in water and uses its forelimbs to prop up the front end of its body when at rest. The animal E which respires by using spiracles and tracheae uses wings for flying but its wings are analogous to the modified forelimbs of animal A.
(a) What could the animals A, B, C, D and E be?
(b) Why are the forelimbs of animals A, B, C and D called homologous organs?
(c) What does the existence of homologous organs in animals A, B, C and D tell us about their ancestors ?
(d) Why are the modified forelimbs of animal A and the wings of animal E called analogous organs?
(e) State whether animals A and E have a common ancestor or not.

Answer:

(a) The animal A could be a bird or a bat, animal B could be lizard, animal C could be human, animal D could be   frog, animal E could be an insect.

(b) Forelimbs of A, B, C, and D are called homologous organs because they have the same basic structure but   different functions.

(c) It suggests that these organisms have evolved from a common ancestor.

(d) It is because forelimbs of animal A and wings of animal E have different basic structures but perform a similar function.

(e) Animals A and E do not have a common ancestor.

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Question 68:

X, Y, and Z are three animals. The animal X can fly but animal Y can only run on ground or walls. The forelimbs of animals X and Y have the same basic design but they are used for different purposes such as flying and running respectively. The animal Z became extinct a long time ago. The study of fossils of Z tells us that it had some features like those of X and some like those of Y. In fact, Z is said to form a connecting link in the evolutionary chain of X and Y.
(a) What could the animals X, Y and Z be?
(b) What name is given to the forelimbs like those of X and Y which have the same basic design but different functions?
(c) Name one feature in which Z resembled X.
(d) Name one feature in which Z resembled Y.
(e) Which is the correct evolutionary chain involving X, Y and Z : X → Z → Y or Y → Z → X?

Answer:

(a) X is birds, Y is reptiles and Z is Archaeopteryx.

(b) Forelimbs like those of X and Y are called homologous organs.

(c) X and Z had feathers.

(d) Z had teeth and tail like Y.

(e) The correct evolutionary sequence is Y → Z → X.

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Question 69:

A population of red beetles lives in green bushes in a garden. Once during the process of breeding, a green beetle is produced.
(a) State whether the change in colour of beetle is a process of evolution or not.
(b) Can the new colour of green beetle be passed on to its next generations?
(c) What will be the advantage (if any) of the green colour to the beetle?
(d) State whether the production of green colour involved a change in genetic material or not.

Answer:

(a) It is a process of evolution. 

(b) The green colour of the beetle is an inherited trait, which can be passed on to the next generation.

(c) It helps in survival of green beetle as it can mixing with green bushes, and hide from predators.

(d) The production of green colour has been brought about by a change in the DNA of the reproductive cells.

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Question 70:

The organs P and Q of two animals have different structures but similar functions. On the other hand, the two organs R and S of two other animals have the same basic structure but different functions.
(a) What are the organs like P and Q known as?
(b) Name the organs like P and Q. Also name the animals which have such organs.
(c) What are the organs like R and S called?
(d) Name the organs like R and S. Also name the animals which have such organs.

Answer:

(a) Organs P and Q are known as analogous organs. 

(b) Wings of an insect and a bird are like P and Q.

(c) Organs R and S are called homologous organs.

(d) Forelimbs of humans and wings of birds are like R and S.



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