VBQs Class 12 Biology Evolution

VBQs For Class 12

Please refer to VBQs for Class 12 Biology Evolution. All value based questions for Biology Class 12 have been provided with solutions. We have provided below important values questions and answers. Students should learn these solved VBQs for Class 12 Biology as these will help them to gain more marks and help improve understanding of important topics.

Evolution VBQs Class 12 Biology with Answers

Origin of Life

Very Short Answer Type Questions

Question. Name the scientist who disproved spontaneous generation theory.
Answer.Louis Pasteur disproved spontaneous generation theory and proved biogenesis.

Question. Write the hypothetical proposals put forth by Oparin and Haldane.
Answer. Hypothetical proposals given by Oparin and Haldane :
(i) Life originated spontaneously from pre-existing non-living organic molecules.
(ii) Formation of life was preceded by chemical evolution.

Short Answer Type Questions

Question. Name the scientist who has used the set-up shown. Write the purpose of ‘a’ in the set-up and the conclusion the scientist arrived at.

Answer. Stanley Miller had used the set up shown. In the figure ‘a’ represents electrodes, used for simulation of lightning. From the experiment, Miller concluded that complex organic molecules were formed from simple inorganic molecules.

Question. Write the Oparin and Haldane’s hypothesis about the origin of life on Earth. How does meteorite analysis favour this hypothesis?
Answer. Oparin and Haldane proposed that life originates from pre-existing non-living organic molecules, such as RNA, proteins etc. and formation of life was preceded by chemical evolution. Meteroite analysis confirmed presence of similar compounds elsewhere in space, maintaining that, life had reached earth in form of spores from other heavenly bodies.

Question. What was proposed by Oparin and Haldane on origin of life? How did S.L. Miller’s experiment support their proposal?
Answer. Oparin of Russia and Haldane of England proposed that the first form of life could have originated 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.
The Oparin-Haldane theory (also called chemical theory or naturalistic theory) was experimentally supported by Stanley Miller. Miller created laboratory conditions similar to primitive earth. Miller used mixture of methane, ammonia, hydrogen and water in an air tight apparatus and passed electrical discharged from electrodes at 800 °C. He passed the mixture through a condenser. He circulated the gases in same way for about a week and then analysed the contents. Formation of simple organic compounds supported chemical evolution of life.

Question. (a) Explain the theory of biogenesis.
(b) How did Miller demonstrate experimentally the chemical evolution that happened three billion years ago? 
Answer.
(a) Louis Pasteur disapproved abiogenesis (spontaneous generation) and put forth the Theory of biogenesis, which states that life originated from pre-existing life. He took broth in a long necked flask and then he bent its neck (swan neck). He boiled the broth in this flask to kill any microorganisms that might be present in it. This flask was kept for months but, no life appeared, as the germ laden dust particles in the air were trapped by the curved neck of the flask that served as filter. If the swan neck was broken off, the broth developed colonies of moulds and bacteria. Thus, he showed that the source of the microorganisms for fermentation or putrefaction was the air and the organisms did not arise from the nutrient media.
(b) Stanley Miller (1953), designed an apparatus for simulating conditions prevalent on earth at the time of abiogenic evolution of organic substances.The apparatus had a spark chamber with two electrodes (for simulation of lightning), a flask for boiling (simulation for evaporation and circulation) and a condenser. A control apparatus was also prepared but without electrodes in the spark chamber. Miller used a mixture of methane, ammonia, hydrogen and water in this apparatus. The mixture was exposed to electric discharges, followed by condensation. It was continued for one week. The experiment was repeated a number of times. The products were extracted and identified through chromatography. He found a large number of simple organic compounds including some amino acids such as alanine, glycine and aspartic aid. Miller proved that organic compounds were basis of life and organic compounds were formed from simple inorganic compounds.

Question. The figure given represents Miller’s apparatus used for his experiment. Name the chemicals found in the samples drawn from ‘c’. How did this experiment support evolution?

Answer. Sample drawn from ‘c’ contained simple organic compounds containing amino acids like alanine, glycine and aspartic acid. This experiment proved chemical evolution of life. Miller proved that organic compounds were basis of life and organic compounds were formed from simple inorganic compounds.

Question. Mention the contribution of S.L. Miller’s experiment on origin of life. 
Answer. Miller’s experiment supported chemical evolution of life. He experimentally showed formation of complex organic molecules from simple inorganic compounds. In a closed flask, he circulated mixture of four gases (H2, CH4, NH4 and water vapour) and passed electric current through it at 800°C. Formation of some amino acids, proved that organic compounds were basis of life.

Short Answer Type Questions

Question. State the theory of Biogenesis. How does Miller’s experiment support this theory? 
Answer. Theory of biogenesis states that life originated from pre-existing forms.
Stanley Miller (1953), designed an apparatus for simulating conditions prevalent on earth at the time of abiogenic evolution of organic substances.The apparatus had a spark chamber with two electrodes (for simulation of lightning), a flask for boiling (simulation for evaporation and circulation) and a condenser. A control apparatus was also prepared but without electrodes in the spark chamber. Miller used a mixture of methane, ammonia, hydrogen and water in this apparatus. The mixture was exposed to electric discharges, followed by condensation. It was continued for one week. The experiment was repeated a number of times. The products were extracted and identified through chromatography. He found a large number of simple organic compounds including some amino acids such as alanine, glycine and aspartic aid. Miller proved that organic compounds were basis of life and organic compounds were formed from simple inorganic compounds.

Question. Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life. 
Answer.
(a) Louis Pasteur disapproved abiogenesis (spontaneous generation) and put forth the Theory of biogenesis, which states that life originated from pre-existing life. He took broth in a long necked flask and then he bent its neck (swan neck). He boiled the broth in this flask to kill any microorganisms that might be present in it. This flask was kept for months but, no life appeared, as the germ laden dust particles in the air were trapped by the curved neck of the flask that served as filter. If the swan neck was broken off, the broth developed colonies of moulds and bacteria. Thus, he showed that the source of the microorganisms for fermentation or putrefaction was the air and the organisms did not arise from the nutrient media.

What are the Evidences for Evolution ?

Very Short Answer Type Questions

Question. State the significance of the study of fossils in evolution. 
Answer.Fossils are remains of organisms of the past buried in different strata of the earth. The study of fossils helps in understanding about the past life.
(i) The fossil records have helped in reconstructing the phylogeny of many organisms e.g., of horse, elephant and man.
(ii) Fossils also indicate the connecting links between two groups of organisms e.g. Archaeopteryx shows features of both reptiles and birds.

Question. State the significance of biochemical similarities amongst diverse organism in evolution.
Answer.  Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry. Biochemical similarities point to the same shared ancestry as structural similarities among diverse organisms and hence show common ancestry and evolution of different groups of organisms.

Question. Why are analogous structures a result of convergent evolution?
Answer. Analogous organs are a result of convergent evolution. Convergent evolution is development of similar adaptive functional structures in unrelated group of organisms. e.g., wings of an insect and wings of bird show convergent evolution, both have similar function but different basic structure. 

Question. 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) Flippers of penguins and dolphins and
(b) eyes of octopus and mammals are analogous organs showing convergent evolution.

Question. 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. 
Answer.  Wing of bird and the forelimb of horse are homologous organs, as both have same fundamental structures but have different functions i.e., for flying in bird and in horse for running. Homology indicates common ancestry and shows divergent evolution.

Question. Identify the examples of homologous structures from the following.
(a) Vertebrate hearts
(b) Thorns in Bougainvillea and tendrils of Cucurbita.
(c) Food storage organs in sweet potato and potato. 
Answer.(a) Vertebrate hearts and (b) thorns of Bougainvillea and tendrils of Cucurbita are homologous organs, indicating common ancestry.

Question. Name any two vertebrate body parts that are homologous to human forelimbs.
Answer.Forelimbs of whale and wings of birds are homologous to human’s forelimbs.

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. Wing of butterfly and wing of bat are analogous organs as they perform similar function of flying but have different origin and structures. Wings of butterfly are composed to chitinous membranes while wings of bat are composed of bony skeleton. This infer that they represent convergent evolution.

Question. How does ‘fitness’ of a population help in evolution?
Answer. The fittest organisms, i.e., the organism with beneficial variations, survives and adapts to ever changing harsh environmental condition. Therefore, fit bettter in an environment, produce more progeny and therefore will survive and hence are selected by the nature.

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.Wing of a cockroach and wing of bird are analogous organs as they have different basic structure but perform same function, and thus show convergent evolution

Question. “Sweet potato tubers and potato tubers are the result of convergent evolution.” Justify the statement. 
Answer. Sweet potato tubers (root modification) and potato tubers (stem modification) shows convergent evolution as both have different structure but perform similar function of storing food. Thus, these structures are analogous.

Question. Explain convergent and divergent evolution with the help of one example of each.
Answer. Divergent evolution is development of different functional structures from a common ancestral form. It represents adaptive radiation. Homologous organs show adaptive radiation or divergent evolution E.g., Darwin’s finches of the Galapagos islands. They had common ancestors but now have different types of modified beaks according to their food habits. Convergent evolution is development of similar adaptive functional structures in unrelated groups of organisms. It is called adaptive convergence or convergent evolution. E.g., wings of insect, bird and bat.

Question. State a reason for the increased population of dark coloured moths coinciding with the loss of lichens (on tree barks) during industrialisation period in England.
Answer. During industrialisation period in England, in the industrial areas, sulphur dioxide pollution from the burning of coal killed the lichens growing on the trees, exposing the darker bark which was further darkened by falling smoke particles. So, white moths were selectively picked up by birds and black moths escaped unnoticed and managed to survive resulting in more population of black moth than white moth.

Question. Are the thorn of Bougainvillea and tendril of Cucurbita homologous or analogous? What type of evolution has brought such a similarity in them? 
Answer. Thorn of Bougainvillea and tendril of Cucurbita are homologous organs. They both arise from axillary position but they perform different functions. Thorns provide protection and tendrils provide support. They have anatomical similarity but differ functionally. Divergent evolution has brought such a similarity in them.

Short Answer Type Questions

Question. Identify the following pairs as homologous and analogous organs:
(a) Sweet potato and potato
(b) Eye of octopus and eye of mammals
(c) Thorns of Bougainvillea and tendrils of Cucurbita.
(d) Forelimbs of bat and whale.
Answer.Homologous organs : (c) Thorns of Bougainvillea and tendrils of Cucurbita, (d) forelimbs of bat and whale.
Analogous organs: (a) Sweet potato and potato, (b) eye of Octopus and eye of mammals.

Question. Select two pairs from the following which exhibit divergent evolution. Give reasons for your answer.
(a) Forelimbs of cheetah and mammals.
(b) Flippers of dolphins and penguins.
(c) Wings of butterflies and birds.
(d) Forelimbs of whales and mammals.
Answer. The organs which exhibit divergent evolution are:
(a) Forelimbs of cheetah and mammals
(d) Forelimbs of whales and mammals
Whales, cheetah, bat and human (all mammals) share similarities in the pattern of bones of forelimbs. Though these forelimbs perform different functions in these animals, they have similar anatomical structure i.e., all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs. Hence, in these animals, the same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. 

Question. Explain with the help of an example the type of evolution homology is based on.
Answer. Homology is based on divergent evolution. It indicates common ancestry. Homologous organs have the same fundamental structure but are different in functions. These organs follow the same basic plan of organisation during their development. But in the adult condition, these organs are modified to perform different functions as an adaptation to different environments. Examples : The forelimbs of man, cheetah, whale and bat have the same basic structural plan. But have different shapes and functions.

Question. (a) Select the homologous structures from the combinations given below :
(i) Forelimbs of whales and bats
(ii) Tuber of potato and sweet potato
(iii) Eyes of octopus and mammals
(iv) Thorns of Bougainvillea and tendrils of Cucurbita.
(b) State the kind of evolution they represent.
Answer.(a) (i) Forelimbs of whales and bats and (iv) thorns of Bougainvillea and tendrils of Curcurbita are homologous organs.
(b) These structures represent divergent evolution, indicating common ancestry, having same fundamental structure but different function.

Question. Explain how natural selection operates in nature by taking an example of white winged and dark winged moths of England. 
Answer. Natural selection is the process by which those organisms that are best suited to their environment and are able to reproduce well in changed environmental conditions, survive. One of the most striking examples, which demonstrates the action of natural selection in the wild is the case of peppered moth, Biston betularia that lives in all parts of England.
Due to industrial smoke and soot the pale tree trunks became more and more blackened. As a result, the light moths stood out in contrast to its background, increasing the possibility of being easily detected and eaten by their predators, such as birds, in much greater number than the dark melanic variety. Decrease in the number of light winged moths and increase in the number of dark variety was the ultimate result. Therefore, evolution favoured the dark winged melanic moths to reproduce more successfully for their adaptation in the polluted areas of England. Evolution of darker form in response to industrial pollution is known as industrial melanism.

Question. 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? 
Answer. Comparative study of forelimbs of bat, horse and human shows common ancestry or common embryonic origin. Bat, horse and human share similarities in the pattern of bones of forelimbs, as they have similar anatomical structure—humerus, radius, ulna, carpals, metacarpals, and phalanges, but perform different functions, (in bat for flying, running in horse and walking in humans). These limbs are categorised as homologous organs as same structure developed along different directions due to adaptations to different needs.

Question. Convergent evolution leads to analogous structures. Explain with the help of an example.
Answer. Convergent evolution is development of similar adaptive functional structure in unrelated groups of organisms, resulting in analogous organs in unrelated organisms, which have similar functions but different developmental patterns. E.g., the wings of bee, bird and bat.

Question. What does the comparison between the eyes of octopus and those of mammals say about their ancestry and evolution? 
Answer. Eyes of octopus and mammals are analogous organs, which represent convergent evolution, i.e., development of similar adaptive functional structures in unrelated group of organisms. These organs have different structure but perform similar functions.

Question. Choose two pairs of homologous structures from the following and mention why they are so called :
(a) Hearts of humans and monkeys
(b) Eyes of octopus and mammals
(c) Thorns of Bougainvillea and tendrils of cucurbits
(d) Flippers of penguins and dolphins.
Answer.(a) Vertebrate hearts i.e., hearts of humans and monkeys and (b) thorns of Bougainvillea and tendrils of cucurbits are homologous organs, as they have same structure but perform different functions.

Question. Divergent evolution leads to homolgous structures. Explain with the help of an example.
Answer. Divergent evolution is development of different functional structures from common ancestral form, as the ancestors migrated to different habitats and organs became modified in adaptations to new requirements. i.e., homologous organs. Different mouth parts of some insects. The mouth parts of cockroach, honey bee, mosquito and butterfly have the same fundamental part. In each of these insects, the mouth parts comprise labrum, a pair of mandibles and two pairs of maxillae, but they have different functions to perform, keeping in view their different feeding habits. The mouth parts in cockroach are adapted for biting and chewing. In honey-bee for chewing and lapping, in mosquito for piercing and sucking, in house-fly for sponging and in butterfly for siphoning.

Question. What is divergent evolution? Explain taking an example of plants.
Answer. When lineages split and evolve along separate adaptive pathways showing increased morphological differences in a given biospace, it is called as divergent evolution. Thorns of Bougainvillea and tendrils of Passiflora are modified branches and are axillary in position. It means axillary branches in Bougainvillea are modified into thorns for protection from burrowing animals and in Passiflora into tendrils for climbing. Presence of homologous organs in different groups confirms that difference in appearance is due to divergent evolution, i.e., the ancestors migrated to different habitats and organs became modified in adaptation to new requirements.

Question. Explain divergent evolution with two examples.
Answer. Divergent evolution is development of different functional structures from a common ancestral form. It represents adaptive radiation. Homologous organs show adaptive radiation. E.g., Darwin’s finches of the Galapagos islands. They had common ancestors but now have different types of modified beaks according to their food habits. Locomotion in mammals is also an example of divergent evolution, as forelimbs of cheetah, whale, bat and man have same structural plan but different functions.

Question. How does palaeontological evidences support evolution of organisms on earth?
Answer.Palaeontology is the study of past life based on fossil records. Their study reveals the type of life forms in past and illustrates the course of evolution of plants and animals.
The distribution of fossils in the rocks of different ages fully supports the concept of evolution. It shows that wing forms became more and more complex as we proceed from earliest to recent. From the fossil records it has been concluded that evolution has taken place from simple to complex in a gradual manner.

Question. Why are thorn of Bougainvillea and tendrils of Cucurbita called homologous? What does this homology indicate?
Answer.  Thorns of Bougainvillea and tendrils of Cucurbita are homologous organs, as both arise in the axillary position but are modified for different functions. Thorns for protection and tendrils as support for climbing. Thus, homology indicates common ancestry and relationship between different groups. Difference in appearance are due to divergent evolution i.e., the ancestors migrated to different habitats and organs became modified in adaptations to new requirements.

Short Answer Type Questions

Question. Explain convergent evolution taking one example for plants.
Answer. Convergent evolution refers to the development of similar adaptive functional structures in unrelated group of organisms. It is also called adaptive convergence. E.g., The cladode of Ruscus are analogous to leaves of other plants. Both look alike and perform the same function of photosynthesis but are different in origin. 

Question. What are analogous structures? How are they different from homologous structures? Provide one example for each.
Answer.Difference between analogous structures and homologous structures.

Question. Explain taking one example of vertebrate anatomy that evolution of life forms has occurred on earth. 
Answer. Study of comparative anatomy and morphology shows similarity and differences among organisms of today and those that existed millions of years ago. These informations give a clue to whether a common ancestor was shared or not. Development of many vertebrate organs (e.g., heart, brain, kidney) indicate the possible path of evolution as well as the common ancestry of vertebrates. For example, during its development, the heart of a mammal or bird is initially two-chambered (as in fishes), then threechambered (as in amphibians and some reptiles) and ultimately four-chambered. It clearly shows that birds and mammals have originated from fishes through amphibians and reptiles.

Question. Differentiate between divergent and convergent evolution. Give one example of each.
Answer. Difference between divergent evolution and convergent evolution.

Question. How does the study of fossils support evolution?
Explain. 
Answer. Fossils refer to the petrified remains or impressions of organisms that lived in past and got preserved in the sedimentary rocks. These include bones, teeth, shells and other hard parts of animal or plant body, and also any impressions or imprints left by previous organisms in the soft mud or the moulds and casts of entire organisms.

Question. The study of
(a) Fossils of dinosaurs
(b) Forelimbs of cheetah, bat, whale and human
(c) Thorns of Bougainvillea and tendril of Cucurbita. 
Show that evolution of life forms has indeed taken place on earth. Explain.
Answer.
(i) Fossils of dinosaurs – Dinosaurs are organisms that existed in the past but are now extinct. The 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 spans.
(ii) Forelimbs of cheetah, bat, whale and human are homologous organs as they share similarities in the pattern of bones, though these perform different functions. This shows divergent evolution.
(iii) Thorns of Bougainvillea and tendrils of Cucurbita are also homologous structures as they both arise from axillary position but in Bougainvillea it helps in prolection but in Cucurbita it helps in support. Homology shows divergent evolution.

Question. Differentiate between homology and analogy.Give one example of each. 
Answer.The differences between homology and analogy are as follows :

Question.

What do these pictures ‘a’ and ‘b’ illustrate with reference to evolution? Explain. 
Answer. In picture ‘a’ the light-coloured species is well adapted to the lighter background of the lichen covered trunks of trees. Here it is not seen by the predatory birds. In contrast, the dark winged moths are quite visible against the lighter background hence, are spotted and picked by the predatory birds. In the industrial areas, as in picture ‘b’ sulphur dioxide pollution from the burning of coal killed the lichens growing on the trees, exposing the darker bark, which was further darkened by the falling smoke particles. Against a dark background, the light-coloured moths are conspicuous and are picked up by the predatory birds. For the survival, nature has favoured the dark-coloured melanic species from the light-coloured species. The former has a much better chance of survival under the new conditions created by pollution. 

Long Answer Type Questions

Question. (a) Anthropogenic actions have caused evolution of species. Explain with the help of two examples.
(b) Differentiate between divergent and convergent evolution. 
Answer. 
(a) Evolution is not a directed process in the sense of determinism. It is a stochastic process based on chance events in nature and chance mutations in the organisms. Anthropogenic actions also leads to evolution. E.g.
(i) Excess use of herbicides, pesticides, etc. has resulted in selection of resistant varieties.
(ii) Resistant varieties of microbes develop against which, antibiotics are applied.
(b)Difference between divergent evolution and convergent evolution.

Question. (a) Differentiate between analogy and homology giving one example each of plant and animal respectively.
(b) How are they considered as an evidence in support of evolution?
Answer.
(a) The differences between homology and analogy are as follows :

(b) Both homologous and analogous organs provide concrete evidence in support of evolution. Homology, (similarity between organs of different animals) indicates common ancestry, or common embryonic origin. Analogy shows that evolution of similar adaptive features in different groups of organisms is due to similar habitat.

What is Adaptive Radiation?

Very Short Answer Type Questions

Question. Name the placental mammals corresponding to the Australian ‘Spotted cuscus’ and Tasmanian ‘tiger cat’ which have evolved as a result of convergent evolution. 
Answer.  Placental mammal Lemur corresponds to Spotted cuscus and Bobcat corresponds to Tasmanian tiger cat.

Question. Write the term used for resemblance of varieties of placental mammals to corresponding marsupials in Australia.
Answer. Adaptive radiation.

Short Answer Type Questions

Question. How do Darwin’s finches illustrate adaptive radiation? 
Answer. 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. Darwin’s finches represent one of the best example of this phenomenon, as many varieties of finches were observed to be present in the same island. All the varieties, evolved on the island itself from the original seed-eating finches that lead to various modifications in the finches according to their food habits. This evolution in finches enabled the birds to become insectivorous, vegetarian, wood pecking, ground feeding etc.

Short Answer Type Questions

Question. What is adaptive radiation? When can adaptive radiation be referred to as convergent evolution? Give an example. 
Answer. The 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 e.g., Darwin’s finches. Adaptive radiation can be referred to as convergent evolution, when more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats). E.g., A number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent.

Question. Name and explain the evolutionary concept represented in the illustration given below:

Answer. Given illustration represents adaptive radiationof Australian marsupials within Australian island continent. A number of marsupials, each different from the other evolved from an ancestral stock, but all within Australian island continent. This pattern occurs when organisms coming from different stocks evolve similar features and adapt to the same habitat. This is also referred to as convergent evolution.

Question. Explain the interpretation of Charles Darwin when he observed a variety of small black birds on Galapagos Islands. 
Answer. During his journey, Darwin went to Galapagos island, where he observed amazing diversity of small black birds called Darwin’s Finches. From original seed-eating birds, many different varieties, with altered beaks arose, such as insectivorous finches, vegetarian finches, etc. Birds of Galapagos Islands influenced Darwin to think about evolutionary change. He reasoned that after originating from common ancestral seed eating stock, the finches must have radiated to different habitats and undergone adaptive changes in their beaks which enable them to become insectivorous, vegetarian, etc. This process of evolution of different varieties of Darwin finches in a given geographical area is called adaptive radiation.

Question. (a) How did Darwin explain adaptive radiation?
(b) Give another example exhibiting adaptive radiation. 
Answer.
(a) 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. Darwin’s finches represent one of the best example of this phenomenon, as many varieties of finches were observed to be present in the same island. All the varieties, evolved on the island itself from the original seed-eating finches that lead to various modifications in the finches according to their food habits. This evolution in finches enabled the birds to become insectivorous, vegetarian, wood pecking, ground feeding etc.
(b) Another example is Australian marsupials. A number of marsupials, each different from the other evolved from an ancestral stock, but all within the Australian island continent.

Biological Evolution

Short Answer Type Questions

Question. Explain Darwinian theory of evolution with the help of one suitable example. State the two key concept of the theory. 
Answer.
Darwinian theory of evolution is based on Natural Selection. For example, resistance of insects to pesticides, when DDT was introduced, it was found to be highly effective against mosquitoes, flies and other insects. However, within a few years, populations of mosquitoes and flies were found to be mostly resistant to it. Other pesticides have also caused development of resistant forms. DDT did not give resistance to mosquitoes but acted as an environmental factor that resulted in natural selection. DDT brought about a change in gene frequencies in the population and gave direction to evolution.
Two key concepts of Darwinian theory of evolution are Branching descent and Natural Selection.

Question. Name the scientist who influenced Darwin and how? 
Answer. Darwin was influenced by a book ‘An Essay On The Principles of Populations’ by Thomas Malthus. In this, he discussed that there are ‘positive checks’ that control geometrically growing population. Darwin noticed the conflict between resources of population and its continued reproductive pressure. Darwin considered that like humans, competition exist among all living things. Thus, work of T.R. Matlhus on human population growth influenced him.

Short Answer Type Questions

Question. Fitness is the end result of the ability to adapt and get selected by nature. Explain with suitable example. 
Answer.  Nature selects for fitness which is the end result of the ability of an organism to adapt and get selected by the nature. For example, a colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component. A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions. In due course of time this variant population outgrows the others and appears as new species.

Question. Branching descent and natural selection are the two key concepts of Darwinian theory of evolution. Explain each concept with the help of suitable example. 
Answer. Branching descent and natural selection are two key concepts of Darwinism. Branching descent refers to convergent evolution. When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats) it is referred to as convergent evolution. E.g., Australian marsupials and placental mammals show convergent evolution.
Natural selection is the process by which those organisms that are best suited to their environment and are able to reproduce well in changed environmental conditions, survive. One of the most striking examples, which demonstrates the action of natural selection in the wild is the case of peppered moth, Biston betularia that lives in all parts of England.
Due to industrial smoke and soot the pale tree trunks became more and more blackened. As a result, the light moths stood out in contrast to its background, increasing the possibility of being easily detected and eaten by their predators, such as birds, in much greater number than the dark melanic variety. Decrease in the number of light winged moths and increase in the number of dark variety was the ultimate result. Therefore, evolution favoured the dark winged melanic moths to reproduce more successfully for their adaptation in the polluted areas of England. Evolution of darker form in response to industrial pollution is known as industrial melanism.

Question. How does Darwin’s theory of natural selection explain the appearance of new forms of life on earth?
Answer. The theory of natural selection is based on the following factors :
(i) Rapid multiplication among organisms leads to population growth.
(ii) Limited environmental resources such as food and space leads to struggle for existence.
(iii) Due to variation, some individuals would adust better than others.
(iv) Variations cause natural selection or survival of the fi0ttest.
(v) Inheritance of useful variation leads to formation of new species.

Question.(a) Natural selection operates when nature selects for fitness. Explain.
(b) The rate of appearance of new forms is linked to the life span of an organism. Explain with the help of a suitable example.
Answer.
(a) During the struggle for existence, only those individuals could survive which exhibit variations that are more beneficial in facing the hardships and rigours of environment or which change to adapt themselves to the changing environmental conditions.
Only the fittest organism survive in changed environmental condition and those unfit are destroyed. During the evolution of reptiles, giant reptiles, the dinosaurs etc., appeared. Majority of them were herbivorous, but due to certain climatic changes, the vegetation disappeared and, therefore, most of them became extinct. However, small animals who could change their feeding habits from herbivorous to carnivorous diet survived, because they could easily get adapted to the changed environment. These, therefore, survived and reproduced successfully and hence were selected by nature.
(b) The rate of appearance of new forms is linked to the life cycle or the life span. Microbes that divide fast have the ability to multiply and become millions of individuals within hours. A colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component. A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions. In due course of time this variant population outgrows the others and appears as new species. is would happen within a few days. For the same thing to happen in a fish or fowl, it would take million of years as life span of these animals are in years. 

Mechanism of Evolution

Very Short Answer Type Questions

Question. Write the basis of origin of variations in organisms as described by Hugo de Vries.
Answer.According to de Veries, mutations are the basis of origin of variations in organisms.

Question. Mention the key concepts about the mechanism of biological evolution/speciation according to (a) de Vries and (b) Darwin.
Answer. 
Hugo de Vries gave mutation theory to explain biological evolution. According to this theory, mutations are large and discontinuous variations (mutations) which appear suddenly and are heritable. Two key concept of Darwin theory of evolution are branching descent and natural selection.

Question. Mention how is mutation theory of Hugo de Vries different from Darwin’s theory of natural selection. 
Answer. According to Hugo de Vries, mutations are sudden and heritable variations which causes evolution, hence called it saltation (single step large mutations). While Darwin’s theory of natural selection states that speciation is due to accumulation of small, directional, and heritable variations, and is a gradual process.

Question. According to De-Vries what is saltation?
Answer.Saltation is single step large mutation that causes species formation, thus causing evolution.

Question. List the two characteristics of mutation that help in explaining evolution. 
Answer. According to mutation theory of evolution:
(i) Mutations are random, inheritable and appear in all conceivable directions.
(ii) Same type of mutations can appear in number of individuals of a species. 

Short Answer Type Questions

Question. Describe the mechanism of evolution as explained by Hugo de Vries.
Answer. Hugo de Vries (1901), on the basis of his experiment on O. lamarkiana put forward mutation theory to explain the mechanism of evolution. According to him, mutation causes species formation (and hence called it saltation) and thus evolution.
These mutations are random and directionless.Salient features of the mutation theory are
(i) Mutations are discontinuous variations and the raw material of evolution.
(ii) Mutations appear all of a sudden. They become operational immediately.
(iii) Unlike Darwin’s continuous variations or fluctuations, mutations do not revolve around the mean or normal character of the species.
(iv) The same type of mutations can appear in a number of individuals of a species.
(v) All mutations are inheritable.
(vi) Mutations appear in all conceivable directions.
(vii) Useful mutations are selected by nature. Lethal mutations are eliminated. However, useless and less harmful ones can persist in the progeny.
(viii) Accumulation of variations produce new species. Sometimes a new species is produced from a single mutation.
(ix) Evolution is a jerky and discontinuous process.

Question. How is Darwin’s theory of natural selection different from it? Explain.
Answer. 
Difference between Hugo de Vries’ mutation theory and Darwinian’s theory are as follows :