Science Ncert Exemplar Solutions for Class 10 Science Chapter 9 Heredity And Evolution are provided here with simple step-by-step explanations. These solutions for Heredity And Evolution are extremely popular among Class 10 students for Science Heredity And Evolution Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science Ncert Exemplar Book of Class 10 Science Chapter 9 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science Ncert Exemplar Solutions. All Science Ncert Exemplar Solutions for class Class 10 Science are prepared by experts and are 100% accurate.

Page No 73:

Question 1:

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

Answer:

Gametes taking part in sexual reproduction are produced through meiosis. During meiosis, the chromosomes of a pair exchange their genetic material.

Hence, the correct answer is option (c).

Page No 73:

Question 2:

Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(a) double fertilisation
(b) self pollination
(c) cross fertilisation
(d) no fertilisation

Answer:

In the given cross, pink flowering plants has two dissimilar forms of the gene controlling flower colour. So, on selfing of two pink flowers, red, pink and white flowers are obtained in the ratio 1:2:1.

Hence, the correct answer is option (b).

Page No 73:

Question 3:

A cross between a tall plant (TT) and short pea 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 pea plant is not governed by gene ‘T’ or ‘t’

Answer:

In a cross between two organisms differing in one pair of contrasting traits, F1 hybrid shows only one of the parental traits and this trait is called the dominant trait. Similarly, in the question, since only tall trait is expressed in the progeny resulting from a cross between a tall plant and a short pea plant, tallness is the dominant trait.

Hence, the correct answer is option (a). 

Page No 73:

Question 4:

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 molecule of fat there is a gene

Answer:

A gene is the segment of DNA which contains the information for a protein. This protein can be an enzyme which takes part in the synthesis of a hormone. Out of given four options, option (d) is incorrect statement.

Hence, the correct answer is option (d).

Page No 73:

Question 5:

If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F1 generation are
(a) round and yellow
(b) round and green
(c) wrinkled and green
(d) wrinkled and yellow

Answer:

From the cross between a round, green seeded pea plant (RR yy) and wrinkled, yellow seeded pea plant, (rr YY),

Parents                         RRyy                               x                              rr YY
                                   Round and green                                     Wrinkled and yellow
Gametes                         Ry                                                         rY

F1 generation              RrYy
                                Round and yellow seed

F1 generation plants will produce round and yellow seeds.

Hence, the correct answer is option (a).

 



Page No 74:

Question 6:

In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome 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:

Human males have 22 pairs of autosomes and one mismatched pair of sex chromosomes- one normal-sized X chromosome and the other short Y chromosomes.

Hence, the correct answer is option (c).

Page No 74:

Question 7:

The maleness of a child is determined by
(a) the X chromosome in the zygote
(b) the Y chromosome in zygote
(c) the cytoplasm of germ cell which determines the sex
(d) sex is determined by chance

Answer:

In humans, the sex of the child is determined by the sex chromosome inherited in the zygote from the father. A human male has X and Y sex chromosomes. If a zygote receives X chromosome from the father, it will develop into a female and if a zygote receives Y chromosome from the father, it will develop into a male.

Hence, the correct answer is option (b). 

Page No 74:

Question 8:

A zygote which has an X-chromosome inherited from the father will develop into a
(a) boy
(b) girl
(c) X- chromosome does not determine the sex of a child
(d) either boy or girl

Answer:

In humans, females produce eggs with X chromosome whereas males produces sperms with either X or Y chromosome. If a zygote receives X chromosome from father, it inherits X chromosome from mother. Thus, a zygote with XX will develop into a girl child.

Hence, the correct answer is option (b).

Page No 74:

Question 9:

Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in evolution
(b) Reduction in weight of the 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:

Reduction in weight of the organism due to starvation do not bring any change in DNA of the gamete so, it is not genetically controlled. Out of the four statements, statement (b) is incorrect.

Hence, the correct answer is option (b).

Page No 74:

Question 10:

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:

Gametes or sex cells are the cells involved in sexual reproduction. These gametes fuse to form a zygote which develops into a new organism. So, any change in the DNA or chromosome numbers of the gametes will be transmitted to the new organism. If this new organism with inherited changes in DNA or chromosome number may not reproduce with the existing members, this will be considered a new species.

Hence, the correct answer is option (a).

Page No 74:

Question 11:

Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are selfed, the F2 progeny will have new combination of characters. Choose the new combination from the following
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green

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

Answer:

The results of selfing F1 plants with round and yellow seeds (RrYy) are as follows:



The new combinations of characters in F2 progeny are round and yellow seeds and wrinkled and green seeds.

Hence, the correct answer is option (b).



Page No 75:

Question 12:

A basket of vegetables contains carrot, potato, radish and tomato.
Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato

Answer:

Homologous structures are those structures which have the common origin. Among the given vegetables, carrot and radish are the roots modified for storage of food, potato is the stem modified for storage of food and tomato is a fruit. So, carrot and radish are the examples of homologous structures.

Hence, the correct answer is option (c).

Page No 75:

Question 13:

Select the correct statement.
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous.
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous.
(c) Wings of birds and limbs of lizards are analogous.
(d) Wings of birds and wings of bat are homologous.

Answer:

The tendrils of a pea plant are leaflets modified into wire-like structures that help the plant cling to a support and climb on it. Phylloclade of Opuntia is a green flattened stem with leaves modified into spines so as to reduce the loss of water by transpiration. Since in both the plants, tendrils and spines have the common origin but perform different functions. So, they are homologous structures.

Hence, the correct answer is option (a).

Page No 75:

Question 14:

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:

Fossils found closer to the surface are more recent than the fossils found in deeper layers. 

Hence, the correct answer is option (b).

Page No 75:

Question 15:

Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction

Answer:

Variations are produced due to inaccuracy in DNA copying mechanism and sexual reproduction. All variations in a species do not confer equal survival advantages. So, statement given as option (a) is not true for variation.

Hence, the correct answer is option (a).

Page No 75:

Question 16:

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:

An organism receives DNA from both the parents so, the traits are influenced by the both maternal and paternal DNA.

Hence, the correct answer is option (c).



Page No 76:

Question 17:

Select the group which shares 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:

Species is the lowest group in the hierarchy of classification. It is a group of individuals that share common characteristics and are capable of interbreeding. Thus, any two individuals of a species share the maximum numbers of related or common characters.

Hence, the correct answer is option (a).

Page No 76:

Question 18:

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:

According to the evolutionary theory, accumulation of variations (resulting from errors in DNA copying and sexual reproduction) over several generations along with operation of natural selection leads to the formation of new species.

Hence, the correct answer is option (b).

Page No 76:

Question 19:

From the list given below, select the character which can be acquired but not inherited
(a) colour of eye
(b) colour of skin
(c) size of body
(d) nature of hair

Answer:

The size of the body of an organisms increases or decreases based on the availability of the food and results from the changes in the non-reproductive tissues. So, these changes cannot be passed on to the next generation. So, it is an acquired character.

Hence, the correct answer is option (c).

Page No 76:

Question 20:

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) two different chromosomes
(c) sex chromosomes
(d) any chromosome

Answer:

An organism inherits two copies of each chromosome, one each from the male and female parents. The two forms of a gene controlling a character (two versions of a trait) are present at the same location on the two copies of one of the chromosomes. At the time of gamete formation, when a chromosome pair segregate and move to different gametes, two forms of a gene also segregate, each gamete receiving one copy of a chromosome along with one form of a gene. When these gametes from two parents fuse, the two copies of the same chromosome along with the two forms of a gene are also brought together in the organsm of the next generation.

Hence, the correct answer is option (a).

Page No 76:

Question 21:

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:

A gene is a segment of DNA that codes for a protein. An organism has a number of genes present on the different chromosomes and each occupies a specific location of a particular chromosome. So, out of given four statements, statements (i) and (iii) are the characteristics of genes.

Hence, the correct answer is option (b).

Page No 76:

Question 22:

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

Answer:


The ratio  of pure tall plants (TT) to short plants (tt) is 1:1.

Hence, the correct answer is option (c).



Page No 77:

Question 23:

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

Answer:

In humans, a gamete has one sex chromosome either X or Y. So, a zygote formed from the fusion of two gametes has two sex chromosomes or a pair of sex chromosomes (XX or XY).

Hence, the correct answer is option (a).

Page No 77:

Question 24:

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

Answer:

Charles Darwin formulated the theory of evolution of species by natural selection based on his observations on the variety of life during his sea voyage to islands.

Hence, the correct answer is option (b).

Page No 77:

Question 25:

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:

Dinosaurs were reptiles. The possible explanation for the given information that some dinosaurs had feathers but they could not fly and birds have feathers that help them fly, is that feathers in dinosaurs start as providing insulation in cold weather and later they become useful for flight in birds. So, in the context of evolution, this means that birds have evolved from reptiles.

Hence, the correct answer is option (d).

Page No 77:

Question 26:

How is the sex of a newborn determined in humans?

Answer:

Sex of a newborn in humans is genetically determined, that is, genes inherited from the parents determine the sex of a baby. If a newborn inherits one X chromosome from mother and X chromosome from father, this newborn will become a girl and if a newborn inherits one X chromosome from mother and Y chromosome from father, this newborn will become a boy.

Page No 77:

Question 27:

Do genetic combination of mothers play a significant role in determining the sex of a new born?

Answer:

Mothers have two X chromosomes as sex chromosomes so, they produce eggs with X chromosome. All of her children (both girl and boy) receive X chromosome from their mother. So, genetic combination of mothers do not play a significant role in determining the sex of a new born.

Page No 77:

Question 28:

Mention three important features of fossils which help in the study of evolution.

Answer:

Important features of fossils that help in the study of evolution:

  • The fossils can be used to determine their age and the time period during which they lived.
  • The fossils provide information about morphology and anatomy of the past organisms which can be used to establish their relationship with the present and past organisms.
  • They provide tangible, physical evidence of ancient life and has provided the basis of the theory of evolution.

Page No 77:

Question 29:

Why do all the gametes formed in human females have an X chromosome?

Answer:

Human females have a pair of X chromosomes as sex chromosomes in addition to 22 pairs of homologous chromosomes (autosomes). During gamete formation, two X chromosomes segregate to different gametes. So, all gametes (eggs) in human females have an X chromosome in addition 22 autosomes.

Page No 77:

Question 30:

In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.

Answer:

In human beings, males possess two sex chromosomes (X and Y) so they produce two types of male gametes - 50%  sperms with X chromosome and 50% sperms with Y chromosome. So, the sex of the child is determined by the sex chromosome present in the male gamete or sperm. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50 : 50, the statistical probability of male or a female infant is also 50 : 50.

Page No 77:

Question 31:

A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.

Answer:

A small population has fewer individuals which breed among themselves. As a result, less variations appear in this population. This poses a threat to the existence of the small population. If there are changes in the environment, the individuals will fail to cope up with the environmental changes, they may become extinct. So, a very small population of a species faces a greater threat of extinction than a larger population.

Page No 77:

Question 32:

What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

Answer:

Homologous structures are those structures which have a common basic structure but perform different functions. For example, forelimbs of reptiles, amphibians and mammals. Yes, homologous structures always have a common ancestor from which they have evolved along different directions due to adaptations to different needs.

Page No 77:

Question 33:

Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.

Answer:

Yes, the occurrence of diversity of animals on earth does suggest their diverse ancestry. Because common ancestry may greatly limit the extent of diversity. As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animals is not the likely theory.

Page No 77:

Question 34:

Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(i) yellow seed
(ii) round seed

Answer:

      Dominant/Recessive
(i)  Given trait Yellow seed Dominant
  Contrasting trait Green Seed Recessive
(ii) Given trait Round seed Dominant 
  Contrasting trait Wrinkled seed Recessive

Page No 77:

Question 35:

Why did Mendel choose pea plant for his experiments?

Answer:

Mendel chose pea plant for his experiments because of the following reasons:

  • This plant can be easily grown.
  • This plant has short life cycle and produces large number of seeds.
  • It can self-fertilise.
  • It has easily distinguishable contrasting traits.
  • Because of its large flower, it can be easily crossed in a controllable manner.



Page No 78:

Question 36:

A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.

Answer:

In humans, women produce one type of eggs (all with X chromosome) and men produce two types of sperms - 50% with X chromosome and 50% with Y chromosome. All the children of a women receive X chromosome from her but second sex chromosome which is received from father, can be X or Y. So, the sex is determined by the sex chromosome present in the sperms of the father. If a woman has only daughters, it means father has contributed sperm with X chromosome.

Page No 78:

Question 37:

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

Answer:

Yes, geographical isolation of individuals of a species lead to formation of a new species. Suppose two sub-populations of beetle living in a mountain become separated by a river and there is very low gene flow between them. Over generations, due to the processes of genetic drift and natural selection, these two populations of beetles become different from each other and they are unable to reproducing with each other even if they happen to meet. Slowly the separated individuals will reproduce among themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

Page No 78:

Question 38:

Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.

Answer:

This is difficult to state that organisms with complex body plan like humans are more evolved than the organisms with simpler body plan like bacteria. If progressive trend in evolution is the emergence of more and more complex body designs, human beings are certainly more evolved than bacteria. But on considering the totality of life characteristics into account, it is hard to label either organism as evolved. Because organisms older designs are not inefficient. Many of the older and simpler designs still survive e.g.,  the simplest life forms, bacteria inhabit the most inhospitable habitats like hot springs, deep-sea thermal vents and the ice in Antarctica. So, human beings are not the pinnacle of evolution, but simply yet another species in the teeming spectrum of evolving life.

Page No 78:

Question 39:

All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.

Answer:

All the human races like Africans, Asians, Europeans, Americans and others share the following characteristics:

  • Common body plan, structure, physiology and metabolism.
  • Constant chromosome number
  • Common genetic blue print
  • Freely inter-breeding
Thus, based on the similarities in the above characteristics, it can be said that all human races might have evolved from a common ancestor.

Page No 78:

Question 40:

Differentiate between inherited and acquired characters. Give one example for each type.

Answer:

Inherited Characters Acquired Characters
Inherited characters are those characters that a person gets from his/her ancestors. Acquired characters are the characters that a person gets during his/her lifetime.
These characters develop due to changes in DNA of germ cells so, these are passed on from one generation to another. These characters do not develop due to changes in DNA of germ cells hence, they are not inherited to the next generation.
Examples - attached or free earlobes, colour of the eye, skin colour, etc. Examples - decrease in weight due to starvation, muscular body, etc.

Page No 78:

Question 41:

Give reasons why acquired characters are not inherited.

Answer:

Acquired characters are those characters that an organism gets during its lifetime. These characters do not bring any change in the DNA of germ cells so these characters are not inherited.

Page No 78:

Question 42:

Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.

Answer:

All living organisms existing on earth show immense diversity in size, form, structure and morphological features but at the molecular
level, these organisms exhibit unbelievable similarity. For instance, these organisms are made up of the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. which show remarkable similarity in all of them. DNA in all organisms is made up of same units (nucleotides) and has the same double-helical structure. So, evolution has exhibited a greater stability of molecular structure when compared with morphological structures.

Page No 78:

Question 43:

In the following crosses write the characteristics of the progeny

Cross      Progeny
(a) RR YY × RR YY ...........................
Round, yellow Round, yellow
...........................
(b) Rr Yy × Rr Yy ...........................
Round, yellow Round, yellow
...........................
(c) rr yy × rr yy ...........................
wrinkled, green wrinkled, green
...........................
(d) RR YY × rr yy ...........................
Round, yellow wrinkled green
...........................

Answer:

(a) Parents -                RRYY           ×              RRYY
                             Round, yellow                   Round, yellow
Gametes -                     RY                                     RY
Progeny -                        RRYY
                                     Round, yellow

(b)  Parents -              RrYy                 ×            RrYy
                              Round, yellow                    Round, yellow

Gametes -              RY, rY, Ry, ry                        RY, rY, Ry, ry
 

  RY rY Ry ry
RY RRYY
Round, yellow
RrYY
Round, yellow
RRYy
Round, yellow
RrYy
Round, yellow
rY RrYY
Round yellow
rrYY
Wrinkled, yellow
RrYy
Round, yellow
rrYy
Wrinkled, yellow
Ry RRYy
Round, yellow
RrYy
Round, yellow
RRyy
Round, green
Rryy
Round, green
ry RrYy
Round, yellow
rrYy
Wrinkled, yellow
Rryy
Round, green
rryy
Wrinkled, greem

(c) Parents -      rryy                 ×          rryy
                    Wrinkled, green               Wrinkled, green

Gametes -           ry                                      ry

Progeny -              rryy
                        Wrinkled, green

(d) Parents -                   RRYY                              ×                rryy
                                 Round, yellow                                       Wrinkled, green
Gametes -                    RY                                                         ry
Progeny -                   RrYy
                             Round, yellow

Page No 78:

Question 44:

Study the following cross and showing self pollination in F1, fill in the blank and answer the question that follows

Parents RRYY × rryy
  Round, yellow   wrinkled, green
F1 – Rr Yy × _?_
  Round, yellow    

Answer:

Parents -                     RRYY                  ×              rryy
                              Round, yellow                        Wrinkled, green

Gametes -                        RY                                           ry

F1-                          RrYy                      ×                         RrYy
                             Round, yellow                                     Round, yellow

Page No 78:

Question 45:

In question 44, what are the combinations of character in the F2 progeny? What are their ratios?

Answer:

The different combinations of characters in F2 progeny are as follows:
(i) Round, yellow – 9 
(ii) Round, green – 3
(iii) Wrinkled, yellow – 3
(iv) Wrinkled, green – 1

F2 Ratio – 9:3:3:1

Page No 78:

Question 46:

Give the basic features of the mechanism of inheritance.

Answer:

Genes present on the chromosomes control characters or traits. A gene controls a character and has two or more forms and one form may be dominant over the other. An individual has two similar or dissimilar forms of a gene controlling a trait, one inherited from each parent. The two forms of a gene separate during gamete formation so that each gamete has only one form. These two forms of a gene are brought together in the zygote when gametes fuse at the time of fertilisation.

Page No 78:

Question 47:

Give reasons for the appearance of new combinations of characters in the F2 progeny.

Answer:

The two or more genes are inherited independent of each other and they recombine in the zygote to form new combinations in F2 generation. For example, when a tall pea plant with round seeds is crossed with a short pea plant with wrinkled seeds, the gene controlling plant height (tall/short) segregate independent of the gene controlling seed shape (round/wrinkled) and they recombine in the zygote to form new combinations (tall and wrinkled seeds and short and round seeds).



View NCERT Solutions for all chapters of Class 10