Evolution (Biology): Solved CBSE Questions from previous Class 12 Board Exams

 

 CHAPTER - EVOLUTION

Class12 Biology : CbseNcertSolution.Com

(Questions taken from previous CBSE Class XII Board Exams)

SECTION-A (1 Mark Question)

Question: Identify the examples of homologous structures from the following -

(i) Vertebrate hearts.

(ii) Thorns in Bougainvillea and tendrils of Cucurbita.

(iii) Food storage organs in sweet potato and potato.

Answer:

(i) Vertebrate hearts,

(ii) Thorns in Bougainvillaea and tendrils of Cucurbita.


SECTION-B (2 Marks Question)

Question: How do Darwin's finches illustrate adaptive radiation?

Answer: Darwin during his journey to Galapagos Islands observed that there were many varieties of small black birds later called Darwin's finches.

All the varieties he conjectured, evolved on the island itself.

From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches.

This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.


SECTION-C (3 Marks Question)


Question: (a) How does the Hardy-Weinberg's expression (p2+2pq+ q2=1) explain that genetic equilibrium is maintained in a population? (b) List any two factors that can disturb the genetic equilibrium.

Answer:

(a) Gene frequencies in a population are stable, constant from generation to generation, until some change in frequency happens, due to some factor.

(b) Gene migration/gene flow/gene drift/mutation/genetic recombination/natural selection.

Question: Comment on the similarity between the wing of a cockroach and wing of a bird. What do you infer from the above, with reference to evolution?

Answer: They are similar in function. Thus, we infer that these organs are analogous which has resulted in convergent evolution.

Question: How does industrial melanism support Darwin's theory of Natural Selection? Explain.

Answer: Before industrial revolution the environment was unpolluted. The lichens on the barks of trees were pale. The white-winged moths could easily camouflage, while the dark-winged were spotted out by the birds for food. Hence, they could not survive. After industrial revolution the lichens became dark (due to soot deposit).

This favored the dark-winged moths while the white-winged were picked by birds. The population of the former which was naturally selected increased.


SECTION-D (5 Marks Question)

Question: Explain the salient features of Hugo De Vries of mutation. How is Darwin's theory of natural selection different from it? Explain.

Answer: Hugo de Vries based his work on evening primrose, brought forth the idea of mutations-differences arising suddenly in a population. He believed large single step mutation called salutation, caused speciation.

Darwin's theory:

(i) Directional

(ii) Gradual / slow.

(iii) Continuous variation.

Hugo De Vries's theory:

(i) Directionless.

(ii) Sudden.

(iii) Random.

Question: (a) Name the primates that lived about 15 million years ago. List their characteristics features.

(b) (i) Where was the first man-like animal found? (ii) Write the order in which Neanderthals, Homo habilis and Homo erectus appeared on earth. State the brain capacity of each one of them. (iii) When did modern Homo sapiens appear on this planet?

Answer:

(a) Dryopithecus & Ramapithecus.

Dryopithecus is ape like and hairy, walked like Gorillas and Chimpanzees

Ramapithecus is more man like.

(b)

(i) Ethiopia/Tanzania/Eastern Africa. (ii) Order of appearance: Homo habilis, Homo erectus, Neanderthals. Cranial capacity: Homo habilis = 650 - 800 cc, Homo erectus = 900 cc, Neanderthals = 1400 cc. (iii) Modern Homo sapiens appeared on this planet during ice age i.e. 75000 - 10000 yrs ago.

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