CBSE Class 10 Science Important Questions Chapter 9 Heredity and Evolution Part 3

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3 Marks Questions

1. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Ans. Variations that confer an advantage to an individual organism may or may not survive in the population depending upon the social behaviour of the organism. A variation in a social animal like ant may not survive in a population while a variation in an animal like a leopard may survive.

2. What are the different approaches to determine evolutionary history of man?

Ans. To construct evolutionary history of man, there are three approaches-

(1) Historical method- It gives direct evidence in the form of fossil records. The age of fossils can be determined by carbon dating methods.

(2) Comparative method- By comparing several existing forms, we can makes ideas about their common ancestors and reconstruct their about possible history.

(3) Analytic method- By observing present day human being vestigial organs and by studying the development pattern from embryo to adult.

3. What is fossilization? How are fossils formed?

Ans. The process of fossils formation is called fossilization. Fossils are formed when organisms die; their bodies get decomposed and lost. Sometimes the body or a part of it may be in such an environment that it does not let it decompose completely. The mud will eventually harden and retain the impression of the body parts of the organism. This mud with the impression will be called fossil of the organism.

4. What are homologous and analogous organ? Explain with the help of example.

Ans. Homologous organs are those which have similar basic structure and origin but may have different functions. For example- Hands of human beings and wings of birds.

Analogous organs- Organs which have different basic structure and origin but have similar function are called analogous organs.

For example - (1) wing of bat and wing of bird.

(2) Wing of birds and wing of insect.

5. Differentiate between convergent and divergent evolution.


Convergent and Divergent Evolution
Convergent EvolutionDivergent Evolution
Adapted for similar function.Adapted for different function
Analogous organ.Homologous organ.
Do not indicate evolutionary relationship.Indicate evolutionary relationship.

6. What are the different ways in which individuals with a particular trait may increase in a population?

Ans. The factors which are responsible for raising a new species are selection of environmental conditions for survival of a particular species. If a variation occurs in a population and that variation results in better survival of the organism in the prevailing natural conditions, then the trait would be selected naturally and more in the population.

7. What are the different theories about origin of life?

Ans. (a) Theory of special creation- According to this theory the almighty god created life.

(b) Theory of spontaneous generation- According to this theory, life originated from nonliving materials by the process of a biogenesis wring mud, decomposing matter, sun, air and water, etc.

(c) Cosmozoic theory- It states that life came to Earth from some heavenly bodies in the form of spores or seeds.

(d) Biogenesis- This theory states that life originated from pre-existing life.

(e) Modern theory of origin of life- According to this, complex organic molecule was formed from simple inorganic molecules only in suitable condition.

8. What is the difference between chemical evolution and organic evolution?


Chemical Evolution and Organic Evolution
Chemical EvolutionOrganic Evolution
It is the formation of the complex organic compound from simple compound or element.It is formation of complex from of life from simple from of life.
It occurred at the time of origin of lifeIt is still occurring.
Speed of evolution is fast.Speed of evolution is slow.

9. Give difference between homologous and analogous organs.


Homologous and Analogous Organs
Homologous organsAnalogous organs
Similar in origin and basic structure but may differ in function.Dissimilar in origin and basic structure but may have similar function.
Provide idea of common ancestry.Do not provide the idea of common ancestry.
For Ex – hands of human beings and forelimbs of horse.For ex – wing of birds and insects

10. State three laws of Mendel.

Ans. Mendel’ s law-

(a) Law of dominance- when two dissimilar factors of a character are present in an organism only one expresses itself (dominant factor) while other remain unexpressed (recessive factor)

(b) Principle of segregation – two factors of a character are separated at the time of gamete formation and each gamete gets only one factor for that character.

(c) Principle of independent assortment- this principle states that inheritance of two or more pair of contrasting traits is such a way that one pair of contrasting traits is independent of the other pair of contrasting traits.

11. Describe how the sex of the offspring is determined in the zygote ins human beings?

Ans. The males can produce two types of gametes, either X-type or Y-type. The females produce only one type of gametes or ova, X-type. If X-type sperm fuses with the ovum, then the sex of the baby will be female. If Y-type sperm uses with the ovum, then the sex of the baby will be male. Sex of the baby is decided at the time. Sex of the baby is decided at the time of fertilization.

12. Give a suitable explanation for “geographical isolation of individual of a species lead to formation of a new species?

Ans. Reproduction barrier such as river (geographical isolation) between the sub population leading to:

(a) Genetic drift or random changes in the gene frequency by chance alone e. g. selection of red or blue beetles instead of green in presence of crows.

(b) Natural selection or selection of the fittest by nature itself eg. Selection of green beetles instead of red ones in the presence of crows.

13. State the evolutionary force which leads to origin of a new species.

Ans. various elemental forces of evolution are –

(a) Mutation

(b) Recombination (Crossing over during meiosis, Random assortment of gene at the time of gamete formation) .

(c) Natural selection or survival of the fittest.

(d) Genetic drift.

14. What is a fossil? How do fossils tell us about the process of evolution?

Ans. The dead remains of former living organisms are called fossils. The branch of biology which deals with the study of fossils is called paleontology. The study of fossils tells us that species arose from previously existing ones or that the evolution has occurred in nature and is still continuing.

15. Give difference between diploid and haploid.


Diploid and Haploid
Two chromosomes set.One chromosome set.
Chromosomes present in pairs.Chromosomes present in singly.
Formed due to mitosisFormed due to meiosis
Found in Human beings and higher plants.Found in lower plants.

16. Who disproved Lamarckism and how?

Ans. The concept of inheritance of acquired character of Lamark was disproved by August Weismann. He cuts the tail of rat at the time of birth and continued this for 21 generation. But tailless rats were never born. This trait do not change the DNA of germ cells so cannot be inherited. Hence, the changes in non-reproductive tissue of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution.

17. How does Archaeopteryx provide evidence for organic evolution?

Ans. Archeoptyrx has some features of reptiles, characters of dinosaurs as well as some features of birds like wings. This shows that birds are closely related to reptiles. Birds could evolve from reptiles.

18. What is divergent evolution? Explain with the help of an example.

Ans. The formation of dissimilar looking organisms from common ancestors is called divergent evolution. This is also known as adaptive radiation which represents evolution of new forms in several directions from the common ancestors type. The current example of such a process is the evolution of wild cabbage. For over more than 200 years, humans have cultivated wild cabbage as a food plant and generated different vegetables (like cabbage, broccoli, cauliflower, kohlrabi and kale etc) from it by different artificial selections. Thus all these structures of different vegetables are descended from the same ancestor i.e.. wild cabbage.

19. What is the difference between reproductive and non-reproductive variations?


Non-Reproductive Variations
Non-Reproductive VariationReproductive Variation
Variation in somatic cells.Variation in germ cells.
Not passed from one generation to another because they do not change the DNA of germs cells.Passed from one generation to another because they change the DNA of germs cells.
Die with the death of the organism.Do not die with the death of the organism.
Cannot direct evolution.Can direct evolution.

20. Write similarities between Mendalian’ s factors and gene.

Ans. Mendel proposed the inheritance of traits from parents to offsprings by hereditary units called factors. Mendel suggested that every character is controlled by a pair of factors. Sutton and Boveri (1902) found striking similarities between the behaviours of Mendelian factors and the chromosomes during meiosis and fertilization. Factor and chromosomes are present in paired condition in the parents, seprate during meiosis and again get paired after fertilization.

21. How does the creation of variations in a species promote survival?

Ans. Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.

22. How do Mendel’ s experiments show that traits may be dominant or recessive?

Ans. In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in generation are tall and in generation, 75% of pea plants are tall but 25% are dwarf. This shows that traits are dominant or recessive.

23. How do Mendel’ s experiments show that traitsare inherited independently?

Ans. When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in generation all the plants have round yellow seeds. But in generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently.

24. 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?

Ans. No, the information is not enough because the blood group is determined by a pair of gene. One inherited from mother and other from father. In this case, the child inherited gene for O blood group from mother as well as father.

25. How is the sex of the child determined in human beings?

Ans. A child which inherits X chromosome from her father will be a girl and one who inherits Y chromosome from him will be a boy.

26. What factors could lead to the rise of a new species?

Ans. Following factors could lead to the rise of new species:

(a) Changes in gene frequency in small breeding isolated populations.

(b) Natural selection

(c) Changes in number of chromosome.

27. Will geographical isolation be a major factor in the speciation of self-pollinating plant species? Why or why not?

Ans. No, because geographical barrier do not allow breeding between such individuals of a population which reproduce sexually. Moreover asexually reproducing organism pass on the parental DNA to offspring which gives no chance of speciation.

28. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Ans. Yes, due to geographical isolation, the two populations are separated. The levels of gene flow between them will decrease. The isolated population will breed with local population resulting in entry of isolated population into new population.

29. What are fossils? What do they tell us about the process of evolution?

Ans. Preserved traces if living organisms are called fossils found closer to the surface of earth are more recent in origin than the fossils we find in deeper layers. Fossils also help us to find evolutionary relation between organisms.

30. A study found that children with light-coloured eyes are likely to have parents with light coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Ans. No, since two copies of traits are inherited from parents, one from mother and the other form father. Unless we know the nature of these two variants of traits we cannot tell which is dominant and which is recessive. Recessive traits appear when both the parents contribute recessive allele. From this statement we can only presume are that both parents are contributing recessive allele.