CBSE Class 12 Biology Evolution Assignment Set 03

Very Short Answer Type Questions

Question. Rearrange the human activities mentioned below as per the order in which they developed after the modern Homo sapiens came into existence during ice age:
(i) Human settlement
(ii) Prehistoric cave art
(iii) Agriculture 
Answer: The order of activities is as follows:
(i) Pre-historic cave art
(ii) Agriculture
(iii) Human Settlement

Question. What is fossil?
Answer: Fossils are the remains or impressions of ancient organisms preserved in sedimentary rocks or other media.

Question. How do we compute the age of a fossil?
Answer: By radiocarbon dating.

Question. Identity the examples of convergent evolution from the following: 
(i) Flippers of penguins and dolphins
(ii) Eyes of octopus and mammals
(iii) Vertebrate brains
Answer: (i) Flippers of penguins and dolphins
(ii) Eyes of octopus and mammals

Question. Mention one example each from plants and animals exhibiting divergent evolution.
Answer: Thorn of Bougainvillea and tendrils of Cucurbita, forelimbs of whales, bats, cheetah and humans (all mammals)/vertebrate hearts/vertebrates brains. (Any one)

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 Bougainvillea and tendrils of Cucurbita.

Question. Write the similarity between the wing of a butterfly and the wing of a bat. What do you infer from the above with reference to evolution?
Answer: Wings of a bird and a bat perform the same function of flying despite their structural dissimilarity.
This infers that they are analogous organs. It can be inferred that it is of convergent evolution.

Question. “Sweet potato tubers and potato tubers are the result of convergent evolution.” Justify the statement.
Answer: Sweet potato tuber is a modified root whereas potato tuber is a modified stem. These are
anatomically different structures but perform the same function of food storage. Therefore, they are the result of convergent evolution.

Question. Comment on the similarity between the wing of a cockroach and the 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. Write the names of the following:
(a) A 15 mya primate that was ape-like
(b) A 2 mya primate that lived in East African grasslands 
Answer: (a) Dryopithecus
(b) Australopithecine/Homo habilis.

Question. How can you say the lobefin fish were the ancestors of amphibian? 
Answer: Lobefins fish have stout and strong fins, so they can move on land and swim in water to maintain a dual lives like amphibians.

Question. Write the characteristics of Ramapithecus, Dryopithecus, and Neanderthal man.
Answer: Ramapithecus: hairy, walked–like gorillas and chimpanzees, more man like.
Dryopithecus: hairy, walked–like gorillas and chimpanzees, more ape-like.
Neanderthal man: brain size is 1400 cc, used hides to protect their body, buried their dead.

Question. (a) Name the ancestors of progymnosperm.
(b) Name the ancestors of herbaceous and arborescent lycopod.
(c) Name the ancestors of cycads
Answer: (a) Psilophyton
(b) Zosterophyllum
(c) Progymnosperm.

Question. (a) Explain “founder effect”.
(b) State Oparin and Haldane Hypothesis.
(c) Describe Stanley and Miller’s experiment and give its significance.
Answer: (a) Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founder and the effect is called founder effect.
(b) Oparin–Haldane’s theory states that the first life form originated from non-living organic molecules like RNA, protein, etc.

Question. Explain the salient features of Hugo de Vries theory of mutation. How is Darwin’s theory of natural selection different from it? Explain. 
Answer: Salient features of theory of Hugo de Vries:
(i) Mutations cause evolution.
(ii) New species originate due to large mutations.

Question. Identify the following pairs as homologous or analogous organs:
(i) Sweet potato and potato
(ii) Eye of octopus and eye of mammals
(iii) Thorns of Bougainvillea and tendrils of Cucurbits
(iv) Forelimbs of Bat and Whale 
Answer: (i) and (ii) are analogous organs.
(iii) and (iv) are homologous organs.

Question. Explain adaptive radiation with the help of a suitable example. 
Answer: • It is the process of evolution of different species in a given geographical area starting from a common point and radiating to other geographical areas (habitats). Examples: 

Question. Why are the wings of butterfly and birds said to be analogous organs? Name the type of evolution of which the analogous organs are a result of. 
Answer: Wings of butterfly and birds are not anatomically similar structures though they perform similar functions. Hence, they are called analogous structures. Analogous organs result from convergent evolution.

Short Answer Type Questions

Question. “Post-industrialisation, the population of melanised moth increased in England at the expense of white-winged moths.” Provide explanations. 
                                                                                     ​​​​​​​​​​​​​​OR
Explain the increase in the numbers of melanic (dark winged) moths in the urban areas of post-industrialisation period in England. 
                 ​​​​​​​                 ​​​​​​​                                                   ​​​​​​​OR
In England, during the post-industrialised period, the count of melanic moths increased in urban areas but remained low in rural areas. Explain.
Answer:  Pre-industrialisation period had more white winged moth against grey lichens on tree trunks.
During industrialisation large amount of soot and smoke deposited on tree trunks, making the bark dark. Against the dark background white moths could easily be preyed upon. Melanised moth could camouflage against dark bark. This natural selection increased their number.

 Question. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Answer: 

Question. Explain convergent evolution with the help of two examples. 
Answer: Different structures evolved similarly due to same functions. This is called convergent evolution.
Examples:
(i) Wings of butterfly and birds.
(ii) Sweet potato (root modification) and potato (stem modification).

Question. Explain the interpretation of Charles Darwin when he observed a variety of small black birds on Galapagos Islands.
Answer: In Galapagos Islands, the small black birds amazed Darwin and he later called them finches. He realised that there were many varieties of finches in the same island. All the varieties evolved on the island itself. This process of evolution was called adaptive radiation, According to Darwin this evolution was based on available resources, food and space. There is survival of the fittest.

Question. Differentiate between the explanations given by Darwin and de vries respectively on the mechanism of evolution.
Answer: Table 7.5: Differences between Darwin’s and de Vries’ theory of evolution  

Question. What is disturbance in Hardy-Weinberg genetic equilibrium indicative of? Explain how it is caused. 
Answer: Disturbance in Hardy-Weinberg equilibrium is an indicator of change of frequency of allele in a population, resulting in evolution.
It is caused by any of the following factors:
(i) Genetic drift
(ii) Gene flow or gene migration
(iii) Mutation
(iv) Genetic recombinations
(v) Natural selection

Question. (a) Write the Hardy–Weinberg principle.
(b) Explain the three different ways in which natural selection can affect the frequency of a heritable trait in a population shown in the graph given below.

Answer: (a) Hardy–Weinberg principle states that the gene pool (total genes and their alleles in a population) remains constant, i.e., the allele frequencies in a population are stable and constant from generation to generation. This biological phenomenon is called genetic equilibrium.
(b) Natural selection can lead to stabilisation (in which more individuals acquire mean character value), directional change (more individuals acquire value other than the mean character value) or disruption (more individuals acquire peripheral character value at both ends of the distribution curve).
For diagram, refer to Fig. 7.8.

Question. (a) What was proposed by Oparin and Haldane on origin of life? How did S.L. Miller’s experiment support their proposal?
(b) Which human chromosome has (i) maximum number of genes, and which one has
(ii) fewest genes?
(c) Write the scientific importance of single nucleotide polymorphism identified in human genome. 
Answer: (a) Theory of chemical evolution or Oparin–Haldane theory: This theory states that life originated from pre-existing non-living organic molecules (e.g., RNA, protein, etc.). S.L. miller conducted an experiment where he created conditions similar to primitive atmosphere in a flask like high temperature, reducing atmosphere consisting of HCl, NH3, etc. When an electric discharge was created at 800°C, after a week, presence of amino acids and complex molecules like sugars, nitrogen bases, pigments, fats were observed in the flask.
(b) Chromosome 1 has most genes (2968) and the Y chromosome has fewest genes (231).
(c) This information promises to revolutionise the processes of finding chromosomal locations for disease-associated sequences and tracing human history.

Question. (a) What are fossils? How are they an evidence for evolution?
(b) “Anthropogenic action can lead to evolution.” Explain with the help of an example.
Answer: (a) Fossils are remains or impression of hard parts of life-forms that existed in past. They are found in rocks.
Study of fossils in different sedimentary layers indicates the geological periods in which they existed and showed that life forms varied over time.
(b) Excess use of herbicides, pesticides, etc., has only resulted in selection of resistant varieties in a much lesser time scale. This is also true for microbes against which we employ antibiotics or drugs against eukaryotic organisms/ cell. Hence, resistant organisms/cells are appearing in a time scale of months or years and not centuries. These are examples of evolution by anthropogenic action.

Question. (i) Natural selection operates when nature selects for fitness. Explain.
(ii) The rate of appearance of new forms is linked to the lifespan of an organism. Explain with the help of a suitable example. 
Answer: (i) Natural resources are limited, populations are stable in size, members of a population vary in characteristics even though they look superficially similar. Theoretically, population will increase exponentially but the population sizes in reality are limited thus leading to competition. Only the ones which are fit and adapt themselves are able to survive. They grow at the cost of others and flourish. This was called as natural selection by Darwin.
(ii) According to Darwin, the fitness of an organism is measured by its reproductive ability. Also the appearance of new forms is linked to the lifespan of an organism. The greater its lifespan,the more it can reproduce and hence, greater new forms would appear. This can be observed in the development of dark-winged moths due to industrial melanism. For details, refer to the above qustion.

Question. (a) How do the observations made during moth collection in pre- and post-industrialized era in England support evolution by Natural Selection?
(b) Explain the phenomenon that is well represented by Darwin’s finches other than natural selection.
Answer: (a) Organisms we see today were created as such.
(b) The process of evolution of different species in a given geographical area starting from a point, radiating to other areas of geography (habitats) is called adaptive radiation. Finches evolved in the same island from original seed eating features. Many other altered beaks arose enabling them to became insectivorous and vegetarian finches.