NCERT Exemplar Solution Class 10 Science Chapter 9
NCERT Exemplar Solution Class 10 Science Chapter 9
NCERT Exemplar Solution Class 10 Science Chapter 9
and Evolution
Soln:
Explanation:
Apart from sexual reproduction other options are type of asexual reproduction where only single parent is
involved. Hence exchange of genetic material takes place in sexual mode of reproduction.
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
Soln:
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’
Soln:
Explanation:
Soln:
Explanation:
Every, protein enzymes and hormones are controlled by specific gene whereas fats are not controlled by gene
hence option d is a wrong statement.
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
Soln:
Explanation:
Round and yellow are the dominant characters hence in f1 generation all seeds will be round and yellow.
6. In human males all the chromosomes are paired perfectly except one. This/these unpaired chromosome
is/are
Soln:
These are sex determining chromosomes that are not paired perfectly due to half size of Y chromosome.
Soln:
Explanation:
If sperm with Y chromosome fertilize the egg zygote will develop into male child. If sperm with X chromosome
fertilize the egg zygote will develop into female child.
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
Soln:
Explanation:
If sperm with Y chromosome fertilize the egg zygote will develop into male child. If sperm with X chromosome
fertilize the egg zygote will develop into female child.
Soln:
Answer is (b) Reduction in weight of the organism due to starvation is genetically controlled
Explanation:
Option b) is a wrong statement because weight loss and gain are controlled by external factors and they are not
controlled genetically.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
Soln:
Explanation:
Evolution will not takes place without change and variation the genetic material. Hence change in genetic material
and variation in chromosome is required for the evolution of new species.
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
Soln:
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
Soln:
Explanation:
They both have similar structure and they both growth beneath the earth( Roots)
Soln:
Answer is (a) Tendril of a pea plant and phylloclade of Opuntia are homologous
Explanation:
Tendril of a pea plant and phylloclade of Opuntia are homologous because they have similar design and origin.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
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
Soln:
Answer is (b) the extinction of organism has occurred thousands of years ago
Explanation:
Older fossils are found deep in the earth. Hence option b) is the right answer.
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
Soln:
Explanation
Statement a) is wrong s because only useful variation have chance of survival. Nature choose the fittest variation
to survive.
Soln:
Explanation:
DNA is contributed to an offspring by both the parents hence traits are contributed by both the parents.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
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
Soln:
Explanation:
Species is the lowest taxon hence members of same species share maximum number of common characteristics.
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
Soln:
Explanation:
New species are formed due to variation in the DNA for several generations. Asexual reproduction will not result
in variation as there are no gametes involved. ) Movement of individuals from one habitat to another will not
affect DNA change hence it cannot be right answer.
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
Soln:
Explanation:
Person’s food habits decide the nature of the body. Regular exercise helps in building muscular body. Body nature
is not transferred to offspring hence size of the body is not inherited.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
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
Soln:
Explanation:
This is the reason behind expression of one progenies in one version and other versions in another progeny.
Soln:
Explanation:
Satement ii) is wrong because genes code for specific proteins. Statement 4 is wrong because chromosomes have
many number of genes.
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
Soln:
Answer is (b) 3 : 1
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
Explanation:
A cross between pure tall plant (TT) and short plant (tt) would produce progenies with following genotypes.
TT(Pure tall), tt( Pure short) andTt ( Mixed tall). This makes the ratio between tall and short plants is 3:1.
23. The number of pair (s) of sex chromosomes in the zygote of humans is
(a) one
(b) two
(c) three
(d) four
Soln:
Explanation:
23rd pair of chromosome determines the sex of the offspring hence it is called as sex chromosome.
Soln:
Explanation:
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
Soln:
Explanation:
Dinosaurs had feathers but could not fly using them. Birds, later adapted the feathers for flight. Since, dinosaurs
were reptiles, this means that birds have evolved from them.
Soln:
Sex of the individual is determined the genes inherited from the parents. If a newborn acquires X
chromosomes from father child will be a female and if newborn receives Y chromosome from father it will be
a male.
27. Do genetic combination of mothers play a significant role in determining the sex of a new born?
Soln:
No Sex of a new born will be determined by the chromosome donated by father. Mothers have XX in their 23 rd
chromosome pair and they always donate One X. But fathers have X And Y in their 23 rd chromosome pair. If
father donates X child will be girl and if father donates Y child will be a boy.
28. Mention three important features of fossils which help in the study of evolution.
Soln:
29. Why do all the gametes formed in human females have an X chromosome?
Soln:
Females possess XX in their 23 pair of chromosome. During meiosis one X chromosome enters each gamete
hence all females gametes possess X chromosome.
30. In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a
suitable explanation.
Soln:
Sex of the offspring is determined by the gamete donated by male. Male possess X and Y chromosomes in their
23rd pair. The ration between X and Y is 1:! Hence the probability of getting either a male or female child is 50:
50.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
31. A very small population of a species faces a greater threat of extinction than a larger population.
Provide a suitable genetic explanation.
Soln:
A very small population of a species faces a greater threat of extinction than a larger population because of the
following reasons
Inbreeding:
Genetic drift:
Small population is vulnerable to sudden change in environment. Because of genetic drift chances of species with
small population may wipe out.
Inbreeding depression:
This lead to negative population growth which is detrimental for the survival of the species with smaller
population.
32. What are homologous structures? Give an example. Is it necessary that homologous structures always
have a common ancestor?
Soln:
Homologous structures are those which has common basic structure and performs different functions. e.g.
fore limbs of reptiles, amphibians and mammals. If they don’t have common ancestry they are called as
analogous structure.
33. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this
point in the light of evolution.
Soln:
Inspite of the fact that animals have different variety of structures they don not have common ancestry. This
is because common ancestry may greatly limit the extent of diversity. Many of the animals are inhabiting the
same habitat, their evolution by geographical isolation and speciation is also not likely. Hence common
ancestry for all the animals is not the likely theory.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
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
Soln:
i) Yellow- dominant
Green- Recessive
ii) Round-dominant
Wrinkled-Recessive
35. Why did Mendel choose pea plant for his experiments?
Soln:
Mendel choose pea plant for his experiments for the following reasons
36. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Soln:
A woman has only daughter; it means egg always received X chromosome from the sperm. If sperm donates X
chromosomes the resultant child will be female and if Sperm donates y chromosome baby will be a male.
37. Does geographical isolation of individuals of a species lead to formation of a new species? Provide a
suitable explanation.
Soln:
Geographical isolation of individual of a species leads to genetic drift. This limits sexual reproduction of the
separated population. This results in separated individuals reproducing among themselves. This leads to formation
of new variation. Accumulation and transfer of these variations through generation will lead to the formation of
new species.
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
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.
Soln:
This is an issue of debate. It depends on the way we evaluate evolution. If complexity of the body is a parameter
then Human are far superior than bacteria. Bacteria has cellular level of organization and humans have organ level
organization.
On the other hand if we consider the ability of survival bacteria have evolved more than human beings. Humans
can live in any environment but with artificial protection. Humans cannot live in harsher climate whereas bacteria
can be found anywhere on earth. They can survive even harsh climates such as
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.
Soln:
All humans races appear to be different but they have evolved from common ancestry. Following are the evidence
to support this view.
40. Differentiate between inherited and acquired characters. Give one example for each type.
Soln:
Soln:
Acquired characters are the results of our body’s response to external stimuli such as food, disease, climate
change. This results in a development of particular trait where change of phenotype is observed. But for
characters to get inherited to generation Genotype of an organism should be changed. In acquired characters there
is no change in the DNA of germ cells. Hence acquired characters cannot be inherited.
42. Evolution has exhibited a greater stability of molecular structure when compared with morphological
structures. Comment on the statement and justify your opinion.
Soln:
Structure which are apparent to our eyes are called morphological structures. Molecular structures are those
biomolecules which are the integral components of organisms. We see lot of diversity all around us. This diversity
is possible because of diversity in morphological structures. This shows that morphological structures are least
stable. Life which began as simple forms on the earth in now composed of many complex forms.
Life has evolved for millions of years but the structure of basic biomolecules such as DNA remains same. A DNA
is same in a human and in a mouse. A protein has same structure in a bird and in a fungi. So, the molecular basis
of life has not changed through all these years. This proves that evolution has exhibited a greater stability of
molecular structure when compared with morphological structure.
Cross Progeny
a) RR YY x RR YY ........................... Round,
yellow Round, yellow
b) Rr Yy x Rr Yy ........................... Round,
yellow Round, yellow
c) rr yy x rr yy ........................... wrinkled,
green wrinkled, green
d) RR YY x rr yy ........................... Round,
yellow wrinkled green
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
Soln:
Cross Progeny
a) RR YY x RR YY ........................... Round, Round, yellow
yellow Round, yellow
b) Rr Yy x Rr Yy ........................... Round, yellow Round, yellow
Round, yellow Round, green
Wrinkled, yellow
Wrinkled, green
c) rr yy x rr yy ........................... wrinkled, green Wrinkled, green
wrinkled, green
d) RR YY x rr yy ........................... Round, yellow Round, yellow
wrinkled green
44.Study the following cross and showing self pollination in F1 , fill in the blank and answer the question
that follows
F1 — Rr Yy x ?
Round, yellow
Soln:
rryy
ry ry ry ry
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RRYY
NCERT Exemplar for Class 10 Science Chapter 9 Heredity
and Evolution
45. In question 44, what are the combinations of character in the F2 progeny? What are their ratios?
Soln:
rryy
ry ry ry ry
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RY RrYy RrYy RrYy RrYy
RRYY
Soln:
47. Give reasons for the appearance of new combinations of characters in the F2 progeny.
F1 plants have round and yellow seeds. Cross between generations can give rise to new combinations in F2
generation with round-yellow, round green, wrinkled yellow and wrinkled green in the ratio of 9 : 3 : 3 : 1.
This shows that the chances for the pea seed to be round or wrinkled do not depend on their chances to be yellow
or green. Hence each pair of alleles is independent of the other pair. This is called as independent assortment.