NCERT Exemplar Solutions Class 10 Science Heredity and Evolution

Multiple Choice Questions..........................

Question 1:  Exchange of genetic material takes place in

(a) vegetative reproduction

(b) asexual reproduction

(c) sexual reproduction

(d) budding 

Solution 1: (c) sexual reproduction 

Other choices, apart from sexual reproduction, include a form of asexual reproduction in which only one parent is involved. As a result, genetic material is exchanged during sexual reproduction.

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 fertilization 

Solution 2: (c) cross-fertilisation

When two pink flowers were crossed, one red, two pink, and one white flower progeny resulted. Cross-fertilization would be the nature of the cross.

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’ 

Solution 3:  (a) tallness is the dominant trait

Only dominant characters are represented in the first progeny of a monohybrid cross.

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 the production of every enzyme, there is a gene.

(d) For every molecule of fat, there is a gene 

Solution 4:  (d) for every molecule of fat there is a gene

Option (d) is incorrect since every protein, enzyme, and hormone is regulated by a specific gene, while fats are not controlled by a gene. 

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 the F1 generation are

(a) round and yellow

(b) round and green

(c) wrinkled and green

(d) wrinkled and yellow 

Solution 5:  (a) round and yellow 

Since round and yellow are the dominant characters, all seeds in the first generation will be round and yellow.

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) 

Solution 6:  (c) (iii) and (iv)

Owing to the half-size of the Y chromosome, there are sex-determining chromosomes that are not perfectly paired.

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 

Solution 7: (b) the Y chromosome in zygote 

The egg zygote will turn into a male child if sperm with the Y chromosome fertilise it. The egg zygote will turn into a female child if sperm with the X chromosome fertilise it.

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 

Solution 8:  (b) girl

The egg zygote will turn into a male child if sperm with the Y chromosome fertilises it. The egg zygote will turn into a female child if sperm with the X chromosome fertilise it.

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 heavyweight progeny

(d) Traits which are not inherited over generations do not cause evolution 

Solution 9:  (b) Reduction in weight of the organism due to starvation is genetically controlled 

Option (b) is incorrect since weight loss and gain are influenced by environmental factors rather than genetic factors.

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) 

Solution 10:  (a) (i) and (ii)

Evolution cannot occur because the genetic material changes and varies. As a result, evolution of new species necessitates changes in genetic material and chromosome variation.

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 a 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) 

Solution 11:  (c) (ii) and (iii)

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 

Solution 12:  (c) Radish and carrot 

They both have a similar structure and expand underneath the earth's surface (i.e. roots).

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

 Solution 13:   (a) Tendril of a pea plant and phylloclade of Opuntia are homologous

 Because of their identical shape and roots, a pea plant's tendon and an Opuntia phylloclade are homologous.

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

 Solution 14:  (b) the extinction of organism has occurred thousands of years ago

 Deep in the earth, older fossils can be found. As a result, choice (b) is the correct answer. 

Question 15:  Which of the following statements is not true with respect to variation? 

(a) All variations in a species have an 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 

Solution 15:  (a) All variations in a species have an equal chance of survival 

 Since only useful variation has a chance of surviving, statement a) is incorrect. To live, nature selects the most adaptable variety. 

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

 Solution 16:  (c) both maternal and paternal DNA 

 Both parents contribute DNA to their offspring, and therefore both parents contribute characteristics to their offspring.

Question 17:  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  

Solution 17:  (a) two individuals of a species

Since species is the lowest taxon, members of the same species have the greatest number of shared characteristics.

Question 18:  According to the evolutionary theory, the 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 

Solution 18:  (b) accumulation of variations over several generations

Several generations of DNA variation result in the formation of new organisms. Since there are no gametes involved in asexual reproduction, there would be no variation.) Individual movement from one ecosystem to another has no effect on DNA transition, so it cannot be the best solution.

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 

Solution 19:  (c) size of body 

The body's essence is determined by a person's eating habits. Regular exercise aids in the development of a muscular physique. Since body nature is not passed on to offspring, body size is not inherited. 

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 

Solution 20: (b) two different chromosomes 

This is the explanation for one progeny's expression in one edition and another progeny's expression in another.  

Question 21:  Select the statements that describe characteristics of genes 

(i) genes are a 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) 

Solution 21:  (b) (i) and (iii)  

Since genes code for particular proteins, statement (ii) is incorrect. Since chromosomes may have any number of genes, statement (iv) is incorrect. 

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 

Solution 22:  (b) 3: 1 

Progenies with the genotypes below will result from a cross between pure tall plant (TT) and short plant (tt). TT (Pure tall), tt (Pure short), and Tt (Pure short) ( Mixed tall). This results in a 3:1 ratio between tall and small plants. 

Question 23:  The number of pair (s) of sex chromosomes in the zygote of humans is

(a) one 

(b) two 

(c) three 

(d) four 

Solution 23:  (a) one 

The identity of the offspring is determined by the 23^rd pair of chromosomes, which is why it is called a sex chromosome. 

Question 24:  The theory of evolution of species by natural selection was given by 

(a) Mendel 

(b) Darwin 

(c) Morgan 

(d) Lamarck 

Solution 24:  (b) Darwin 

Mendel proposed heredity rules. 

Morgan discovered a drosophila mutation. 

The use and disuse theory was proposed by Lamarck. 

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 

Solution 25:  (a) reptiles have evolved from birds  

Dinosaurs had wings, so they couldn't fly. The feathers were later modified for flight by birds. Dinosaurs were reptiles, which suggest that birds descended from them. 

Short Answer Questions..........................

Question 26:  How is the sex of a newborn determined in humans? 

Solution 26:   The individual's sex is determined by the genes he or she inherited from their parents. If a newborn receives X chromosomes from the father, the child will be female; if the newborn receives Y chromosomes from the father, the child will be male. 

Question 27:   Do genetic combination of mothers play a significant role in determining the sex of a newborn? 

Solution 27:    The chromosome donated by the parent will not decide the sex of a newborn. Mothers' 23rd chromosome pair contains XX, and they still donate One X. Fathers, on the other hand, have the X and Y chromosome pairs in their 23rd chromosome pair. If the father donates X, the child is a girl, and if the father donates Y, the child is a boy. 

Question 28:  Mention three important features of fossils which help in the study of evolution. 

Solution 28: 

• Fossils are extinct animals that have been preserved. 

• Fossils aid in the identification of evolutionary variations between animals and their forefathers and mothers. 

• Fossils are used to determine how long a species lived. 

Question 29:  Why do all the gametes formed in human females have an X chromosome? 

Solution 29:   In their 23 pairs of chromosomes, females have XX. Since each gamete receives one X chromosome during meiosis, all female gametes have an X chromosome.  

Question 30:  In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation. 

Solution 30:   The gamete donated by the male determines the sex of the offspring. The 23rd pair of chromosomes in males are X and Y. The proportion of X to Y is 1:1. As a result, the chances of having a male or female child are 50:50. 

Question 31:   A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation. 

Solution 31:    Because of the following factors, a very small population of a species poses a greater threat of extinction than a larger population. 

Inbreeding: 

Inbreeding is encouraged by a small population. Inbreeding leads to fewer variants.

Genetic drift: 

Genetic drift occurs when a small population is exposed to a rapid shift in the climate. Genetic drift may result in the extinction of small-population species.

 Inbreeding depression:

 This causes negative population growth, which is harmful to the survival of small-population organisms.

Question 32:  What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor? 

Solution 32:   Homologous structures have the same basic structure as each other but execute different functions. Reptiles, amphibians, and mammals, for example, have forelimbs. They are referred to as similar structures if they do not have a common ancestor.

Question 33:  Does the occurrence of the diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution. 

Solution 33:   Animals do not have a common ancestor, despite the fact that they have a wide range of systems. This is due to the fact that shared heritage can severely restrict diversity. Since all of the species share the same environment, evolution through geographical isolation and speciation is unlikely. As a result, shared ancestry for all species is unlikely.

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 

Solution 34: 

(i) Yellow is dominant 

     Green is Recessive 

(ii) Roundness is dominant 

      Wrinkled ness is Recessive 

Question 35:  Why did Mendel choose pea plant for his experiments? 

Solution 35:   Pea plants were chosen for Mendel's experiments because they are easy to grow, have a short life cycle, and produce larger flowers. Pea plants are also self-pollinated. 

Question 36:   A woman has only daughters. Analyse the situation genetically and provide a suitable explanation. 

Solution 36:   The fact that a woman has only one daughter suggests that the embryo has already obtained the X chromosome from the sperm. If sperm donates X chromosomes, the child will be female; however, if sperm donates Y chromosomes, the child will be male. 

Long Answer Questions..........................

Question 37:  Does geographical isolation of individuals of a species lead to the formation of a new species? Provide a suitable explanation. 

Solution 37:   Genetic drift occurs when individuals of a genus are isolated geographically. This restricts the divided population's sexual reproduction. Separated individuals reproduce among themselves as a result of  this. This results in the emergence of a new variation. New organisms will emerge as a result of the accumulation and transmission of these variations across generations. 

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. 

Solution 38:   This is a contentious subject. It all depends on how we assess evolution. If the body's complexity is a criterion, humans are much superior to bacteria. Bacteria organise themselves on a cellular basis, while humans organise themselves on an organ level. On the other hand, bacteria have evolved faster than humans in terms of survival capacity. Humans can survive in any climate as long as they are protected artificially. Humans are unable to survive in harsher environments, while bacteria can be found anywhere on the planet. They can withstand extreme environments including hydrothermal vents and sulphur springs. 

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. 

Solution 39:   While all human races tend to be distinct, they all share a common ancestor. The evidence in support of this viewpoint is as follows. 

• Brain size is comparable. 

• Bipedal movement 

• The presence of body hair. 

• The ability to work with materials. 

• The ability to connect through words. 

• Extremely complicated social conduct. 

• Body construction is the same. 

Question 40:  Differentiate between inherited and acquired characters. Give one example for each type.

Solution 40:

Question 41: Give reasons why acquired characters are not inherited. 

Solution 41:  Our bodies' responses to external stimuli such as food, illness, and climate change result in acquired characters. This leads to the emergence of a specific trait characterised by phenotypic transition. However, in order for characters to be passed on from generation to generation, the organism's genotype must be altered. The DNA of germ cells does not alter in acquired characters. As a result, acquired characters cannot be passed on.

Question 42:  Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion. 

Solution 42:   Morphological structures are structures that are visible to our eyes. Molecular structures are biomolecules that are essential parts of living organisms. We are surrounded by a lot of diversity. Because of the variation in morphological structures, this diversity is possible. This demonstrates that the least stable structures are morphological structures. On the earth, life started as simple forms and has evolved into several complex forms.

While life has evolved over millions of years, the structure of basic biomolecules like DNA has not changed. The DNA of a human and a mouse is identical. A protein in a bird and a fungus has the same structure. So, for all these years, the molecular basis of life has remained unchanged. When opposed to morphologic evolution, this shows that molecular structure has become more stable.

Question 44:  Study the following cross and showing self- pollination in F1, fill in the blank and answer the question that follows:

Parents RRYY x rryy

Round, yellow wrinkled green

F1 — Rr Yy x ?

Round, yellow 

Solution 44:

Question 45:  In question 44, what are the combinations of character in the F2 progeny? What are their ratios? 

Solution 45:

(i) Round yellow — 9

(ii) Round green — 3

(iii) Wrinkled yellow — 3

(iv) Wrinkled green — 1

9 : 3 : 3: 1

Question 46:  Give the basic features of the mechanism of inheritance. 

Solution 46:   The following are the basic characteristics of the inheritance mechanism:

• Characters are regulated by genes.
• Genes exist in two or more forms.
• One type of a gene can be dominant over the others.
• Genes are found on chromosomes.
• Each gene exists in two types, which may be identical or dissimilar.
• At the time of gamete development, two types of the gene differ.
• In the zygote, two types of genes are brought together.

Question 47:  Give reasons for the appearance of new combinations of characters in the F2 progeny. 

Solution 47:   The seeds of F1 plants are round and yellow. In the F2 generation, crosses between generations will result in new combinations of round-yellow, round green, wrinkled yellow, and wrinkled green in the ratio of 9: 3: 3: 1.

This demonstrates that whether a pea seed is round or wrinkled is unrelated to whether it is yellow or green. As a result, each pair of alleles is unrelated to the other. This is referred to as a self-contained assortment.