Short Answer -Class 10 -Science-Biology-Chapter 8 :Heredity and Evolution

Class 10 -Science-Short Answer -Biology-Chapter 8 :Heredity and Evolution

Q1. (a)Explain giving examples how artificial selection has helped in the formation of newer varieties of cauliflower.

 (b) List the steps involved in the formation of new species.

 (c) How different races of human beings belong to the same species?

Ans :  a. Formation of newer varieties, e.g., Broccoli, cauliflower, red cabbage, etc. by man.

 b. Migration, gene flow, natural selection, new species.

c. Capable of interbreeding among themselves.

Q2. a.Why traits such as intelligence and knowledge cannot be passed on to the next generation?

b. How can we say that birds are closely related to reptiles and have evolved from them?

Ans :

a. Traits such as intelligence and knowledge are not heritable traits, which do not bring upon any changes in the DNA of the germ cells and, therefore, cannot be passed on to the progeny.

b. This can be said because traits such as feathers were first seen in reptiles like Dinosaurs, which performed the function of providing insulation to them in cold weather although they could not fly using the feathers but later birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptiles.

Q3. What is speciation? Discuss any two factors that lead to speciation.

Ans :   Speciation means creation of new species from pre exiting ones.

The two main factors which could lead to the formation of a new species are natural selection leading to accumulation of adaptation in geographically separated populations of a species and development of reproductive barrier among them.

Complete separation of sub-populations of a spice (Genetic drift) and difference in way of Natural selection in them for many generations results in speciation i.e. formation of new species that cannot interbreed under natural conditions.

Q4 Fore limbs of amphibians, reptiles, birds and mammals show similarity in their bones but Wings of bat and bird don’t. What conclusion can be drawn from such observation regarding their ancestry?

Ans:

The organs which have similar basic structure and mode of origin but perform different functions in different animals are called homologous organs, e.g., forelimbs of amphibians, reptiles, birds and mammals. Homologous organs give evidence of common ancestry and evolutionary relationship between apparently different species. Analogous organ are the organs in different organisms which have different basic structure but have similarity in shape and function, e.g., wings of bat and bird. These organs do not provide an evidence in support with common ancestry.

Q5. What are fossils?

b. Explain the importance of fossils in evolutionary relationship.

Ans : a. Impressions of the body parts of the organisms and preserved traces of the living organisms are called fossils.

b. The presence of fossilized remains of the organism is the evidence of existence of organisms million years ago which have now become extinct. Fossils also help in determining the connecting links between various groups and their origin from their primitive ones.

Q6. We cannot pass on to our progeny the experiences and qualifications earned during our lifetime”. Justify the statement giving reason and examples.

Ans :  Acquiring knowledge / skill in one’s lifetime such as learning dance, music, physical fitness or any other suitable example. Reason:

a.     Such characters / experiences acquired during one’s lifetime do not bring any change in the DNA of the reproducing cell/germ cell.

b.    Only germ cells are responsible for passing on the characters from the parents to the progeny.

Q7. Give reasons for the following:

a. Traits acquired during lifetime of an individual are not inherited.

b. All the human beings belong to a single species.

c. Variations keep on accumulating during reproduction and do not disappear in next generation.

 Ans :   a. These are acquired traits that do not make any change to the DNA of an organism.

b. Homo sapiens originated in Africa and spread across the globe in stages. The humans with different colours in different regions have come into being as an accident of evolution, so that they could live their lives the best they could. So all belong to the same species.

c. Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. So the changes keep on accumulating generations after generations.

Q8. Explain with an example for each, how the following provides evidences in favour of evolution in organisms:

a. Homologous organs

b. Analogous organs

c. Fossils

Ans :  a. Homologous organs – study of homologous organs suggests that the organs having same structure but performing different functions have evolved from a common ancestor. Example: forelimbs of a frog, lizard, bird and man.

b. Analogous organs – show adoption of organs for common use. Example: wings of butterfly and wings of bat.

c. Fossils – provide the missing links between two species. Example: – Archeopteryx / fossils of some dinosaurs with feathers.

Q9. Variation is useful for the useful over long time. But the variants have unequal chances of survival. Explain this statement.

Ans :  Variation are minor differences among members of a population.

They are useful for the process of evolution which take place over long time. But some of the variants find it more advantageous in the present environmental conditions to survive than others variants by virtue of the variation possessed by them hence they have unequal chances of survival.

Thus some get selected and others get eliminated. Those which survive pass their genes to next generation therefore frequency of genes possessed by them increase in frequency in the population.

 Example – in a population of beetles, a new variation (green colour) get survival benefit/advantage to green beetles whereas other (red) perishes.

Q10. Give reasons for the following:

a. Traits acquired during lifetime of an individual are not inherited.

b. All the human beings belong to a single species.

c. Variations keep on accumulating during reproduction and do not disappear in next generation.

Ans :  a. These are acquired traits that do not make any change to the DNA of an organism.

b. Homo sapiens originated in Africa and spread across the globe in stages. The humans with different colours in different regions have come into being as an accident of evolution, so that they could live their lives the best they could. So all belong to the same species.

c. Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. So the changes keep on accumulating generations after generations.