CBSE Class 12 Biology Evolution Question Bank

CBSE Class 12 Biology Evolution Question Bank. There are many more useful educational material which the students can download in pdf format and use them for studies. Study material like concept maps, important and sure shot question banks, quick to learn flash cards, flow charts, mind maps, teacher notes, important formulas, past examinations question bank, important concepts taught by teachers. Students can download these useful educational material free and use them to get better marks in examinations.  Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

Biology: Chapter 7 – Evolution (Question Bank)

1 mark questions
Identify the examples of convergent evolution from the following:
(a) Flippers of penguins and dolphins
(b) Eyes of octopus and mammals
(c) Vertebrate brains

Answer: (a) and (b).

What did Louis Pasteur's experiments on killed yeast demonstrate? Name the theory that was disproved on the basis of his experiment.

Answer: They showed that life comes only from pre-existing life. The theory of spontaneous generation was disproved.

The coelacanth was caught in 1938 in South Africa. Why is it very significant in the evolutionary history of vertebrates?

Answer: The coelacanth is a fish with stout, strong fins that could be used to move on land and go back to the water. It is thought to be related to the ancestors of the first amphibians. It was thought to be extinct, so it is a living fossil.

List the two characteristics of mutation that help in explaining evolution according to De Vries.

Answer: Mutations are random and directionless.

Why are lichens regarded as pollution indicators?

Answer: Lichens are very sensitive to pollutants such as sulphur dioxide, so they do not grow in polluted areas. Their presence shows that the air is clean.

Pick out the ancestral line of angiosperms from the list given below: conifers, seed ferns, cycads, ferns.

Answer: Seed ferns.

Mention the type of evolution that has brought about the similarity seen in a potato tuber and a sweet potato.

Answer: Convergent evolution. The potato tuber (a stem) and the sweet potato tuber (a root) are analogous structures, which have evolved for the same function.

2 marks questions
List the two main propositions of Oparin and Haldane.

Answer:

1. The first form of life could have come from pre-existing non-living organic molecules, such as RNA and proteins.
2. The formation of life was preceded by chemical evolution, that is, the formation of diverse organic molecules from inorganic constituents.

How does palaeontological evidence support the evolution of organisms on Earth?

Answer: Palaeontology is the study of fossils. Fossils show (i) the geological time period in which the organisms existed, (ii) that life forms varied over time, and certain life forms are restricted to certain geological time periods, and (iii) that new forms of life have appeared at different times in the history of the earth. This supports evolution.

What does the comparison between the eyes of an octopus and those of mammals say about their ancestry and evolution?

Answer: The eyes of an octopus and of mammals are analogous structures, which have resulted from convergent evolution. They have not evolved from a common ancestor.

Categorise the following pairs of examples as convergent or divergent evolution:
(a) Eyes of an octopus and of mammals
(b) Wings of a butterfly and of birds
(c) Tuber of sweet potato and of potato
(d) Thorns in bougainvillea and tendrils in cucurbits

Answer:

How do Darwin's finches illustrate adaptive radiation?

Answer: Adaptive radiation is the process of evolution of different species in a given geographical area, starting from a point and radiating to other areas of geography (habitats). Darwin's finches were small black birds that Darwin observed on the Galapagos Islands. A single ancestral seed-eating finch reached the islands. Living in isolation for a long time, new kinds of finches evolved, with different beaks adapted to different food, and they could survive in the new habitats.

How does the fitness of a population help in evolution?

Answer: According to Darwin, fitness refers ultimately and only to reproductive fitness. Those that are better fit in an environment will outbreed the others and leave more progeny. They survive better and are selected by nature to reproduce, so their population size increases, and the population slowly changes over generations.

How is genetic drift different from gene flow (gene migration)? Explain.

Answer:

3 marks questions
State the theory of abiogenesis. How does Miller's experiment support this theory?

Answer: The theory of chemical evolution (abiogenesis) was proposed by Oparin and Haldane. It states that the first form of life could have come from pre-existing non-living organic molecules like RNA and proteins, and that the formation of life was preceded by chemical evolution, that is, the formation of diverse organic molecules from inorganic constituents.
Miller's experiment:

1. He created conditions similar to those of the primitive earth in the laboratory.
2. An electric discharge was produced in a closed flask containing methane, hydrogen, ammonia and water vapour.
3. The temperature was kept at 800°C.
4. After a week, he observed the formation of amino acids.
5. Such molecules must have reacted among themselves to form giant, self-replicating molecules, and then the first form of life.

Evolution is the change of gene frequencies in a population in response to changes in the environment, in a time scale of years and not centuries. Justify the statement with reference to DDT. How does the theory of Hugo de Vries support this?

Answer: As the environment changes, the organisms that are better adapted to the changed environment survive better and reproduce.

1. When DDT was used, most of the mosquitoes died at first, but a few survived.
2. These few mosquitoes reproduced, and their offspring were also resistant to DDT.
3. Today, the population of mosquitoes mostly consists of DDT-resistant mosquitoes.
4. So DDT-resistant mosquitoes evolved in a time scale of years or months, and not centuries. Evolution is not a directed process; it is a stochastic process based on chance events.

According to Hugo de Vries, evolution occurs due to mutations, which are large differences arising suddenly in a population. A large, single-step mutation, called saltation, could have been the cause of DDT resistance in the mosquitoes.

How did Darwin's theory of natural selection explain the appearance of new forms on the earth?

Answer: Darwin's theory of natural selection:

1. Any population has built-in variation for every character.
2. The individuals with those characters that enable them to survive better would outbreed the others, which are less adapted.
3. Fitness, according to Darwin, is reproductive fitness: individuals that are better fit in an environment leave more progeny than the others.
4. So nature selects the better-fit individuals, and over a long period of time, through a number of generations, the population slowly changes into a different form, or a new species. This is evolution.

5 marks question
(a) How does the Hardy–Weinberg equation explain genetic equilibrium?
(b) Describe how this equilibrium gets disturbed, which may lead to the founder effect.

Answer: (a) The Hardy–Weinberg principle states that the allele frequencies in a population are stable and remain constant from generation to generation. This is called genetic equilibrium. The sum total of all the allele frequencies is one. For two alleles with frequencies p and q, \(p+q=1\), and the genotype frequencies are \(p^2+2pq+q^2=1\). The equilibrium is disturbed by gene flow, genetic drift, mutation, genetic recombination and natural selection.
(b) Genetic drift is the change in allele frequencies that occurs only by chance events. Sometimes the change in the allele frequency is so different in the new sample of the population that they become a different species. The original drifted population becomes the founder of the new population, and this effect is called the founder effect.

Value-based question
The giant squirrel (Ratufa indica) occurs along the west coast. The population living in the moist deciduous forests of Maharashtra has light brown fur, the population living in the dry deciduous forests of Gujarat has yellow fur, and the one living in the wet evergreen forests of Kerala has chocolate brown fur.
(a) Give reasons for the difference in the fur colour of the squirrels.
(b) How would you justify that, despite these differences, they all belong to the same species?
(c) What value is indicated in this?

Answer:

1. The differences in the colour of the fur are adaptations to the different habitats. The colour acts as camouflage against the background, so the animals can escape from their predators.
2. Although they differ in fur colour, they can interbreed in nature and produce viable, fertile offspring. So they belong to the same species.
3. Nature provides protection to all life forms.