NCERT Class X Science Class: Chapter –9. Heredity and Evolution – Part-7

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Question 32:

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


Structures which have a common basic structure but perform different functions are called homologous structures. e.g. fore limbs of reptiles, amphibians and mammals. Yes, they have common ancestor but variously modified to carry out different activities.

Image the homologous structures

Image the Homologous Structures

Question 33:

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


Though animals have a vast diversity in structures they probably do not have a common 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.

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


Contrasting Traits of the Following Characters in Pea Plant
Contrasting traits of the following characters in pea plant















Question 35:

Why did Mendel choose pea plant for his experiments?


(a) Easy to grow

(b) Short life span

(c) Easily distinguishable characters

(d) Larger size of flower

(e) Self-pollinated

Image why mendals choos pea plant to study

Image Why Mendals Choos Pea Plant to Study

Question 36:

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


(a) The woman produces ova with ‘X’ chromosome

(b) The man produces sperms with X and Y chromosome which actually determines the sex of the baby.

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