Evolution  Important Questions for CBSE Class 12 Biology The Origin of Life and Evidences of Evolution

1.The study of history of life forms on earth is called evolutionary biology.

2.Evolution is a process that results in heritable changes in population spread over many generations leading to diversity of organisms on earth.

3.Origin of life is considered a unique event in the history of universe.
(i)The Universe

  • It is very old-almost 20 billion years ago. It contains huge galaxies.
  • Galaxies contain stars and clouds of gas and dust.
  • The origin of universe is explained by Big Bang theory.
  • The Big Bang theory states that a huge explosion occurred, the universe expanded, temperature came down and hydrogen and helium were formed later. The galaxies were then formed due to condensation of gases under gravitation.

(ii)The earth was supposed to have been formed about 4.5 billion years back in the  solar system of the milkyway galaxy.

  • Water vapour, methane, carbon dioxide and ammonia released from molten masses covered the surface.
  • UV rays from the sun broke up water molecule into hydrogen and oxygen and lighter hydrogen escaped.
  • Oxygen combined with ammonia and methane to form water, carbon dioxide and others.
  • Ozone layer formed, as it cooled, the water vapour fell as rain to fill depression and form oceans.
  • Life appeared 500 million (about 4 billion years back) years after the formation of earth.

4.Theories of origin of life were given by different thinkers and scientists.
(i)Theory of special creation states that God created life by his divine act of creation.
(ii)Theory of panspermia/cosmozoic theory, given by early Greek thinkers states that the spores or panspermia came from outer space and developed into living forms.
(iii)Theory of spontaneous generation states that life originated from decaying and rotting matter like straw, mud, etc.

  • Louis Pasteur rejected the theory of spontaneous generation and demonstrated that life came from pre-existing life.
  • In his experiment, he kept killed yeast cells in pre-sterilised flask and another flask open into air. The life did not evolved in the former but new living organisms evolved in the second flask.

(iv)Theory of chemical evolution or Oparin-Haldane theory states that life originated from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution.
The conditions on the earth that favoured chemical evolution were very high temperature, volcanic storms and reducing atmosphere that contained CH4,NH3, water vapour, etc.

5.Miller’s experiment provided experimental evidence for chemical evolution.
(i)The experiment was carried out by SL Miller and HC Urey in 1953.
(ii)He took a closed flask containing CH4,H2,NH3 and water vapour at 800 °C and created electric discharge. These conditions were similar to those in primitive atmosphere.
(iii)After a week, formation of amino acids were observed. Complex molecules like sugars, nitrogen bases, pigments and fats were seen in the flask by other scientist.
(iv)Analysis of the meteorite also revealed the presence of similar compounds.
(v)Chemical evolution of life was more or less accepted.
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6.Origin of First Cell
(i)First non-cellular life forms originated three million years ago.
(ii)These molecules were like RNA, protein and polysaccharides.
(ii)Cellular life form first evolved about 2000 million years ago.
(iv)These were single-celled formed in aquatic environment.
(v) This form of abiogenesis, i.e. the first form of life arose slowly through evolutionary  forces from non-living molecules It is accepted by many scientists.

7.Evidences of evolution come from
(i) Palaeontology                                                 (ii) Comparative anatomy and morphology
(iii) Biochemical/Physiology                 (iv) Biogeography
(v) Embryology

(i)Palaeontology is the study of fossils. The fossils are the remains of past organisms  preserved in sedimentary rocks

  • Rocks form sediments and a cross-section of earth’s crust indicates the arrangement of sediments one over the other during the long history of earth.
  • Different aged rock sediments contain fossils of different life forms, who died during the formation of the particular sediment,
  • Some organisms appear similar to modern organisms. They represent extinct organisms like dinosaurs.
  • A study of fossils in different sedimentary layers indicates the geological period in which they existed.
  • The study showed that life forms varied over time and certain life forms are restricted to certain geological time-scale Hence, new forms of life have evolved at different times in the history of earth,

(ii)Comparative anatomy and morphological evidences show the similarities and  differences among the organisms of today and those that existed years ago.
The evidences come from comparative study of external and internal structure.
I.(a) The organs with same structural design and origin but different functions are called homologous organs. Examples are forelimbs of some animals like whales, bats and cheetah have similar anatomical structure, such as humerus, radius, ulna, carpals, metacarpals and phalanges.
(b)Homology in organ indicates common ancestry.
(c)Other examples of homology are vertebrate hearts or brains. In plants also, thorns and tendrils of Bougainvillea and Cucurbita represent homology.
(d)Homology is based on divergent evolution. The same structure developed along different directions due to adaptations to different needs. The condition is called divergent evolution.
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II.(a) Organs which are anatomically different but functionally similar are called analogous organs. For example, wings of butterfly and birds.
(b)Analogy refers to a situation exactly opposite to homology.
(c)Analogous organs are a result of convergent evolution. It is the evolution in which different structures evolve for same function and hence, have similarity.
(d)Other examples of analogy are eyes of Octopus and mammals; flippers of penguins and dolphins. In plants, sweet potato (root modification) and potato (stem modification)
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III.Vestigial organs like homologous organs provide evidences for organic evolution.
These are degenerate, non-functional and rudimentary organs to the possessor, while correspond to fully developed and functional organs of related organisms.
(a)There are about 90 vestigial organs in the human body. Same of them are tail bone (coccyx), wisdom teeth, nictitating membrane, vermiform appendix, etc.
(b)Some examples from other animals are hip girdles and bones of the hind limbs in some whales and certain snakes and wings of flightless birds.
(iii)Biochemical Evidences

  • The metabolic processes in organisms are similar with same new materials and end products. For example, energy released by oxidation is stored in ATP which then powers the energy requiring process.
  • Molecular homology is the similarity among animals at the molecular level.

For example, human DNA differs in only 1.8% of its base pairs from chimpanzee DNA and there is no difference between the two in the amino acid sequence for the protein cytochrome-c.
(iv)Biogeographical evidences The species restricted to a region develop unique features. Also, species present in far separated regions show similarity of ancestry.
This can be explained with the help of following processes:
I.Adaptive radiation is an evolutionary process in which an ancestral stock gives rise to new species adapted to new habitats and new ways of life. Examples are
(i) Darwin’s finches These were small black birds, which Darwin observed in Galapagos island.

  • He observed many varieties of finches in the same island.
  • All varieties of finches had evolved from original seed-eating finches.
  • There was alternation in beaks enabling some to become insectivorous and some vegetarian.

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(ii)Marsupials of Australia A number of marsupials, different from each other evolved from an ancestral stock, all within the Australian island continent.
II.Parallel evolution refers to independent development of similar characters in two animal groups of common ancestry living in similar habitats of different continents. Examples are
Marsupial mammals in Australia show parallel evolution as they have evolved from placental mammals. All these closely resemble and look similar to a corresponding marsupial.
Few examples are mentioned in the table.
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III.Convergent evolution is development of similar adaptive functional structures in unrelated groups of organisms. Examples are:

(i) Wings of insect, bird and bat.

(ii) Spiny anteater and scaly anteater belong to different orders of class-Mammalia. They have acquired similar adaptations for food, e.g. leg ants, termites and insects.

(v) Embryological evidences Study of comparative embryology shows common patterns of development.

  • The principles of embryonic development were given by Von Baer.
  • Ernst Haeckel propounded The theory of recapitulation or Biogenetic law which states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny), i.e. ontogeny recapitulates phylogeny.
  • This means that the life history of an animal reflects its evolutionary history.

For example, during the life history, frog’s tadpole larva resembles fishes, the ancestors of amphibia.The presence of gill clefts in all vertebrate embryos including human provides a strong evidence in support of organic evolution.

(vi)Anthropogenic evidences Excess use of herbicides, pesticides, etc has resulted in selection of resistant varieties in a lesser time scale. This is also true for microbes against which antibiotics or drugs have been used. All these evidences tell us that ‘Elvolution is a stochastic process based on chance events in nature and chance mutation in the organisms’.

Previous Year  Examinations Questions
1 Mark Questions

1.Why are analogous structures a result of convergent evolution?[All India 2014]
Ans.When two species have structures that are  similar in function but differ in origin and anatomy are called analogous structures. This is because both move from different areas to a habitat where they adapt themselves accordingly, therefore it is called convergent evolution.

2.Name the type of evolution that, has  resulted in the development of structures like wings of butterfly and bird. What are such’structures Called?   [Delhi 2014 C]
Ans.Convergent evolution has resulted in the  development of structures like wings of butterfly and bird and such structures are called analogous organs.

3.State the significance of the study of  fossils in evolution.  [Delhi 2012]
Ans.Fossils help us to know the morphological  details of the organisms in the past and relate them to the organisms in the present for understanding the process of evolution. We can also trace the time at which the organism existed.

4.State the significance of biochemical similarities among diverse organisms in evolution.[Delhi 2012]
Ans.Similarities in biochemicals such as DNA, helps in deriving the line of evolution. Organisms with more similar DNA sequences are considered close relatives or have evolved from the same ancestor,

5.Write the similarity between the wing of a butterfly and the w*ng of a bat. What do  you infer from the above, with reference to evolution?[Delhi 2012]
or
Comment on the similarity between the wings of a cockroach and the wings of a bird. What do you infer from the above, with reference to evolution?  [All India 2012]
or
Comment on the similarity between the flippers of dolphin and penguins, with reference to evolution.       [Foreign 2012,2009]
Ans.Similarity between the wings of both the  organisms is that they perform similar functions. They are thus, analogous organs. With reference to evolution, it can be inferred that these are result of convergent evolution

6.Name the scientist who disproved spontaneous generation theory.[Delhi 2010]
Ans.Louis Pasteur disproved the spontaneous  generation theory.

7.Why are wings of butterfly and wings of bat called analogous?[Delhi 2009]
Ans.They are called analogous because they  perform similar functions, but are dissimilar in their development and basic structure.

8.Mention the type of evolution that has brought the similarity as seen in potato tuber and sweet potato.[Delhi 2009]
Ans.Convergent evolution has bought the  similarity as seen in potato tuber and sweet potato.

9.Are the thorn of Bougainvillea and  tendrils of Cucurbita homologous or analogous? What type of evolution has brought such a similarity in them?   [HOTS; Delhi 2009]
or
Are the wing of a bird and the forelimb of a horse homologous or analogous? Name the type of evolution that explains the development of such structures.[Foreign 2009]
Ans.They are homologous. Divergent evolution has brought this similarity in them

10.Name any two vertebrate body parts  that are homologous to human forelimbs.   [All India 2008]
Ans.Wings of birds and forelimbs of horses are  homologous to human forelimb.

11.Name the placental mammals corresponding to the Australian spotted Cuscus and Tasmanian tiger cat, which have evolved as a result of convergent evolution.[All India 2008 C]
Ans.Australian spotted cuscus – Lemur  Tasmanian tiger cat – Bob cat.

2 Marks Questions

12.Identify the following pairs as homologous of analogous organs:
(i)Sweet potato and potato.
(ii) Eye of Octopus and eye of mammals.
(iii)Thoms of Bougainvillea and ‘ tendrils of Cucurbits.
(iv)Forelimbs of bat and whale.[Delhi 2014]
Ans.The given pairs are identified as
(i) Analogous organs.
(ii) Analogous organs.
(iii) Homologous organs.
(iv) Homologous organs.

13.What was proposed by Oparin and  Haldane on origin of life? How did SL Miller’s experiment support their proposal? [Foreign 2014]
Ans.Oparin and Haldane proposed that life originated on earth sponataneously from non-living matter, i.e. organic molecules. SL Miller conducted an experiment where he created conditions similar to primitive atmosphere, in laboratory such as high temperature, reducing atmosphere
consisting of CH4, NH3, etc. When he created a electric discharge in the flask containing all of these at 800 °C. Organic molecules, e.g. amino acids were formed. This supports the above hypothesis that life could have originated from organic matter.

14.List the two main propositions of  Oparin and Haldane.               [All India 2013]
Ans.Two main propositions of Oparin and Haldane were
(i) The primitive atmosphere was reducing,
i.e.free oxygen was absent.
(ii) There was high temperature, high methane, ammonia and hydrogen gas in the atmosphere.

15.Write the Oparin and Haldane’s hypothesis about the origin of life on earth. How does meteorite analysis favour this hypothesis? [All India 2013]
Ans.Oparin-Haldane theory states that origin of  life is the result of a long series of physicochemical changes, brought about first by chemical evolution and then by biological evolution.
Analysis of meteorites also revealed the presence of similar compounds as found in the atmosphere, indicating occurrence of similar processes else where in space.

16.Write about the ancestry and evolution of bat, horse and human on the basis of a comparative study of their forelimbs. What are these limbs categorised as? [Delhi 2013c]
Ans.Bat, horse and human (all mammals) share  similarities in the pattern of bones of forelimbs. Though these forelimbs perform different function in these animals, they have similar anatomical structure, i.e. all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.

17.Divergent evolution leads to homologous stmctures. Explain with the help of an example.[All India 2011 C]
Ans.Divergent evolution is a process where the same structure develops along different directions in different organisms due to adaptations to different needs.  Divergent evolution leads to homologous structures, as they all have similar anatomical structure and origin, but perform different functions.
Examples, the thorn of Bougainvillea and tendrils of Cucurbita are homologous organs as both of them are modified stem which perform different functions.

18.Convergent evolution leads to analogous stmctures. Explain with the help of an example. [All India 2011 c]
Ans.Convergent evolution is a process of evolution, where anatomically dissimilar structures in different organisms perform similar functions.
It leads to analogous structures, in different group of organisms as they perform similar function, but are anatomically different,Example, potato (stem modification) and sweet potato (root modification), flippers of penguins and dolphins

19.Mention the contribution of SL Miller’s experiments to origin of life.[Delhi 2010]
Ans.SL Miller’s experiment provided experimental evidence for chemical evolution. Result of the experiment showed that the first non-cellular forms of life were created about three million years ago. Experiment also demonstrated that non-cellular biomolecule exist in the form of DNA, RNA, polysaccharides and proteins.

20.Why are wings of butterfly and birds said to be analogous organs? Name the type of evolution the analogous organs are a result of. [Foreign 2010]
Ans.Wings of butterfly and birds are analogous structures because they are morphologically different but performs same function.i.e, flying. It occurs due to convergent evolution.

21.What is adaptive radiation? How did  Darwin explained this process of evolution? [Delhi 2008 C]
Ans.Adaptive radiation is the process of  evolution of different species in a given geographical area starting from a point and radiating to other habitats.Darwin went to Galapagos islands and observed that there were many varieties of finches in the same island. All the varieties evolved on the island itself. Darwin reasoned that after originating from a common ancestral seed eating stock, the finches must have radiated to different geographical areas and undergone adaptive changes in their beaks enabling some to become insectivorous.

22.(i) Explain adaptive radiation with  the help of suitable example.
(ii)Cite an example where more than one adaptive radiations have occurred in an isolated geographical area. Name the type of evolution your example depicts and state why it is so named?  [All India 2014]
Ans.(i)The process of evolution of different  species in a given geographical area starting from a point and literally radiating to other areas or habitat is called adaptive radiation such as alterations in beaks of finches on Galapagos island.
(ii) An example where more than one adaptive radiations have occur in an isolated geographical area is Australian Marsupials, where a number of different marsupials evolved from an ancestral stock but within the isolated Australian island, but adapted to different habitats, e.g. Tasmanian wolf (marsupial) and placental wolf (placental mammals).
The above cited example depicts convergent evolution as these marsupials show development of similar adaptive functional structures in unrelated groups of organisms

3 Marks Questions

23.Given below is a diagrammatic representation of the experimental set-up used by SL Miller for his experiment
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(i)Write the names of different gases contained and the conditions set for the reaction in the flask A.
(ii)State the type of organic molecule he collected in the water at B. [Delhi 2013C]
(iii)Write the conclusion he arrived at. [Foreign 2011]
Ans.(i)Gases are methane, ammonia,  hydrogen and water vapour. In ‘A’ flask-electric discharge is created using electrodes.
(ii) The organic molecules collected in water at’B’ are amino acids.
(iii) He concluded that life could have come from pre-existing non-living organic molecules and their formation was preceded by chemical evolution.

24.State the theory of biogenesis. How does Miller’s experiment support this theory?[Delhi 2012]
or
State the views of Oparin and Haldane on evolution. How does SL Miller’s experiment support their views?   [Delhi 2011 c]
Ans.The theory of biogenesis was proposed by Oparin and Haldane. It states that life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was preceded by chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents.
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In 1953, Urey and Miller conducted an experiment to prove this theory. They created the conditions of primitive earth-high temperature, volcanic storms, reducing atmosphere containing CH4, NH3, etc. at laboratory scale. They then stimulated electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 800 °C. They observed formation of amino acids. In similar experiments, others observed formation of sugars, nitrogen bases, pigment and fats. These small organic molecules are the building blocks for proteins and other components. Hence, this experiment supported that life has came from pre-existing non-living organic molecules

25.Convergent evolution and divergent evolution are the two concepts explaning organic evolution. Explain each one with the help of an example.[Foreign 2011; Delhi 2010]
Ans.Divergent evolution is a process where the same structure develops along different directions in different organisms due to adaptations to different needs.  Divergent evolution leads to homologous structures, as they all have similar anatomical structure and origin, but perform different functions.
Examples, the thorn of Bougainvillea and tendrils of Cucurbita are homologous organs as both of them are modified stem which perform different functions.
Convergent evolution is a process of evolution, where anatomically dissimilar structures in different organisms perform similar functions.
It leads to analogous structures, in different group of organisms as they perform similar function, but are anatomically different,Example, potato (stem modification) and sweet potato (root modification), flippers of penguins and dolphins

26.Explain adaptive radiation and convergent evolution by taking example of some of Australian marsupials and Australian placental mammals. [Foreign 2010]
or
Australian marsupials and placental mammals are suitable examples of adaptive radiation and convergent evolution. Explain giving reasons.  [All India 2010 c]
or
(i)What is adaptive radiation?
(ii)Explain with the help of a suitable example, where adaptive radiation has occurred  to represent convergent evolution.  [Delhi 2009 c]
Ans.The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitat) is called adaptive radiation. Australian marsupials are a good example.
Many Australian marsupials, each different from the other, e.g. kangaroo, sugar glider, etc. evolved from a common ancestral stock, but all within the Australian island continent.
When more than one adaptive radiation occur in an isolated geographical area, it can be called as convergent  evolution.
Australian placental mammals also show adaptive radiation in evolving into varieties of such placental mammals, each one of which appear similar to a corresponding marsupial, e.g. placental wolf and Tasmanian wolf, anteater and numbat, etc.

27.Anthropogenic action hasten evolution. Explain with the help of suitable
example.   [Foreign 2010]
Ans.Human activities’ i.e. anthropogenic action are found to enhance evolution.
For example,
(i) Excessive use of DDT as a fertiliser in crops resulted in evolution of DDT resistant mosquitoes.
(ii) Evolution of antibiotic resistant microbes occur due to overuse of antibiotics.

  • When DDT was used first time, many mosquitoes died, but few survived.
  • Survived mosquitoes showed resistance to DDT and reproduced in presence of DDT.
  • Offspring produced by these mosquitoes were also resistant to DDT.
  • Hence, DDT is not affective on mosquito population today

28.(i) Mention the specific geographical region, where these organisms are found.
(ii)Name and explain the phenomenon that has resulted in the evolution of such diverse species in the region.
(iii)Explain giving reasons the existence of placental wolf and Tasmanian wolf sharing  the same habitat.   [Delhi 2009]
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Ans.(i) Australia
(ii) The phenomenon responsible for evolution to such diverse species in the region is the adaptive  radiation. It is evolutionary phenomenon in which different species are evolved in a given geographical area starting from a point and literally radiating to other habitats in that area.
(iii) Tasmanian wolf and placental wolf share same habitat since, they exhibit adaptive radiation and evolved into varieties.

29.(i)Write your observations on the variations seen in the Darwin’s finches shown  below.
(ii) How did Darwin explain the existence of different varieties of finches on Galapagos islands? [All India 2009]
or
Darwin observed a variety of beaks in small black birds inhabiting Galapagos islands. Explain what conclusion did he draw and how?   [All India 2009]
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Ans.(i)Darwin’s finches show variations in beaks due to adaptation to different food habits.
(ii) Darwin’s explanation

  • All the varieties must have evolved within the same island itself. The original finches were  seed-eating. From them, some arose with altered beaks as insectivorous and some as vegetarian finches.     .
  • This process of evolution of different species in a given geographical area starting from a point  and radiating to other habitats is called adaptive radiation.

30.The study of
(i)fossils of dinosaurs.
(ii) forelimbs of cheetah, bat, whale and human.
(iii) thorns of Bougainvillea and tendril of Cucurbita.
Shows that evolution of life forms has indeed taken place on earth. Explain.[Alt India 2008 C]
Ans.(i) Fossils of dinosaurs provide palaeontological evidences for evolution. Different aged rock  sediments contain fossils of different life forms who probably died during the formation of the particular sediment. Some of them appear similar to modern organisms. They represent extinict organisms (e.g. dinosaurs).
(ii) Forelimbs of cheetah, bat, whale and human provide evidences from comparative anatomy and morphology. These organisms share similarities in the pattern of bones of forelimbs. Though these forelimbs perform different functions in these animals, they have similar anatomical structure.
(iii) Thorns of Bougainvillea and tendril of Cucurbita provide evidences from comparative anatomy and morphology. The thorns of these plants represent homology. They are not anatomically similar structures, though they perform similar functions. Hence, analogous structures are a result of convergent evolution.
These evidences indicate that the evolution of life forms has indeed taken place on earth
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