Heredity & Evolution
NCERT Exemplar Problems
Long Answer
Part 1
Question 1: Does geographical isolation of individuals of a species lead to formation of a new species? Provide a suitable explanation.
Answer: Geographical isolation of individuals of a species has the potential to lead to formation of a new species. Turtles of the Galapagos Islands show a good example of speciation due to geographical isolation. Turtles on different islands were geographically isolated. Individuals from one island could not meet with those from another island. So, genetic flow between different groups of turtle could not take place. Over several generations, the degree and types of variations were markedly different in different groups. This led to formation of new species. Turtles on different islands represent altogether different species.
Question 2: 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.
Answer: It depends on how do we view evolution. If complexity of body design is the benchmark for evolution then human beings are more evolved than bacteria. While bacteria have the most simple body design, human beings have the most complex body design. However, if ability to survive in extreme conditions is the benchmark for evolution then bacteria score much higher compared to human beings. While human beings can survive only in certain conditions, bacteria can survive even under the most extreme conditions. Many bacteria are known live in sulphur springs and in craters of volcanoes. From this perspective, bacteria appear to be more evolved than human beings.
Question 3: 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.
Answer: The fact that all human beings on this earth have the capability to interbreed shows that all of them belong to the same species. As they belong to the same species, they show the maximum number of common characters. Some of the common characters in all human beings are as follows:
- Similar size of brain.
- Bipedal locomotion.
- Hair on body.
- Ability to handle tools.
- Ability to communicate using language.
- Highly complex social behaviour.
- Same body design.
Similarity in traits indicate towards common ancestry for all human beings; irrespective of the races they belong to.
Question 4: Differentiate between inherited and acquired characters. Give one example for each type.
Answer:
| Inherited characters | Acquired characters |
|---|---|
| These traits alter the genotype and phenotype. | These traits alter the phenotype only. |
| These traits are transmitted to the next generation. | These traits are not transmitted to the next generation. |
| These traits are the result of genetic recombination. | These traits are the result of organism's response to environmental challenges. |
| Example: hair colour, eye colour, skin colour. etc. | Example: muscular body, ability to excel in a certain field, etc. |
Question 5: Give reasons why acquired characters are not inherited.
Answer: As the name suggests, acquired characters appear in an individual because of his/her response to the external stimuli. These traits develop because of constant exposure to a certain stimulus and the resultant response by the individual. Let us take the example of a wrestler. The wrestler develops good physique because of continuous exercise and suitable diet. Given proper exposure and opportunities, the wrestler may be able to excel in his chosen field. But this does not mean that the son of the wrestler would do equally well in wrestling. He may end up being a cricketer or a film star.
Acquired characters do not bring any change in the germ cells. Hence, acquired characters are not inherited from one generation to the next generation.
Question 6: Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Answer: Morphological structures are those structures (in an organism) which can be easily seen by us. Molecular structure; as the name suggests; are at molecular level. We know that various biomolecules are required to make an organism.
Whatever diversity we see around us is because of diversity in morphological structure. Life began as simple forms; as unicellular organisms. Gradually, it evolved into many complex organisms. Thus, it can be said that morphological structures show the least stability.
However, when we look at the molecular level all the organisms are made up of same biomolecules. DNA, protein, lipid, carbohydrates, etc. are present in all organisms. The structure of DNA is same in every organism, albeit the number of DNAs varies from one organism to another. Irrespective of the type of organism, a DNA molecule or a protein molecule would have the same structure. Hence, it can be said that molecular structures show great stability.