CBSE Class 12 Biology Evolution Assignment Set D

Very Short Answer Type Questions

Question. Why are analogous structures, a result of convergent evolution ?
Answer : Analogous structures are a result of convergent evolution because they are not anatomically similar structures though they perform similar functions. 
Detailed Answer :
Analogous structures are said to be the result of convergent evolution because, though they perform a similar function but they are different in their structural details and origin e.g. wings of insects, birds and bats.

Question. Identify the examples of homologous structure from the following :
(i) Vertebrate hearts.
(ii) Thorns of Bougainvillea and tendrils of Cucurbita.
(iii) Food storage organs in potato and sweet potato
Answer : (i) Vertebrate hearts.
(ii) Thorns of Bougainvillaea and tendrils of Cucurbita are homologous organs. They are similar in origin but different in function. They indicate common ancestry and divergent evolution. 

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 : Similar in function (fly) / different in structure and origin / analogous organs, convergent evolution.
Detailed 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 and are the result of convergent evolution. 

Question. State the significance of biochemical similarity amongst diverse organisms in evolution.
Answer : The biochemical similarities in proteins and genes performing a given function among diverse organisms gives a clue that they share a common ancestry as evolution of diverse group of organisms. 

Question. State two postulates of Oparin and Haldane with reference to origin of life.
Answer : (i) First form of life could have come from pre-existing non-living organic molecules such as RNA & Protein.
(ii) Formation of life was preceded by chemical evolution or formation of diverse organic molecules from inorganic constituents. 

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. Is sweet potato analogous or homologous to potato tuber ? Give reasons to support your answer.
Answer : Analogous, sweet potato-root modification, potato tubers – stem modification. They are structurally different but both are functionally similar as they both store food. 

Question. What is chance mutation ? Explain this phenomenon using application of D.D.T. as an example.
Answer : DDT is an insecticide-kills most of the insects but some become resistant varieties in much less time scale of just month or years. It is a chance event in nature-so chance mutation. 

Short Answer Type Questions

Question. (i) Select the homologous structures from the combinations given below:
(a) Forelimbs of whale and bat
(b) Tuber of potato and sweet potato
(c) Thorns of Bougainvillea and tendrils of Cucurbita.
(ii) State the kind of evolution they represent
Answer : (i) (a) Fore limbs of whale and bat and
(b) Thorns of Bougainvillaea and tendrils of Cucurbita are homologous organs.
(ii) They represent divergent evolution as they have same fundamental structure, common ancestry but different functions. 

Question. What do the forelimbs of whales, bats and cheetah with respect to evolution signify ? Provide one such example in plants.
Answer : Homologous organs or divergent evolution. 
Thorns of Bougainvillea and tendrils of Cucurbita / any other suitable correct example. 

Question. The figure given in question no. 8 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 : Chemicals found in the samples drawn from ‘c’ are sugar, proteins and amino acids.
It provided experimental evidences for the theory of chemical evolution of life. It proved that life originates from pre-existing life. 

Question. Write the Oparin and Haldane’s hypothesis about the origin of life on earth. How does meteorite analysis favour this hypothesis?
Answer : Oparin–Haldane theory of chemical evolution states that life originated from pre-existing nonliving organic molecules.
In 1953, S.L. Miller observed formation of amino acids from CH₄, H₂, NH₃ and water vapour at 800°C.
It states that life originated from pre-existing nonliving organic molecules (e.g., RNA, protein, etc.).
When the meteorites were analysed, there were similar compounds which conclude that similar process is going on elsewhere in the space. 

Question. What does the comparison between the eyes of octopus and those of mammals say about their ancestry and evolution ?
Answer : The eyes of octopus and those of mammals show convergent evolution. They are different in origin and structures which have evolved for the same function and hence have similarity. They are thus analogous structures and they do not share any common ancestry and are thus a result of convergent evolution. 

Question. Choose two pairs of homologous structures from the following and mention why they are so called?
(i) Heart of humans and monkeys
(ii) Eyes of octopus and mammals
(iii) Thorns of Bougainvillaea and tendrils of cucurbits
(iv) Flippers of penguins & dolphins.
Answer : Following are homologous organs :
(iii) Thorns of Bougainvillaea and tendrils of cucurbits.
(iv) Flippers of penguins and dolphins.
They are homologous organs because they are similar in origin and fundamental structural plan but due to their different need they have developed differently, hence different in functions. They indicate divergent evolution. 

Question. Select two pairs from the following which exhibit divergent evolution. Give reasons for your answers.
(i) Forelimbs of cheetah and mammals
(ii) Flippers of dolphins and penguins.
(iii) Wings of butterflies and birds.
(iv) Forelimbs of whale and mammals.
Answer : (i) Forelimbs of cheetah and mammals.
(iv) Forelimbs of whales and mammals.
All these animals show similarities in pattern of bones of forelimb but they perform different functions. They have similar anatomical structure.
Hence, the same structural organs in these animals have developed in different directions because of adaptations to their different requirements. This shows thus the divergent evolution and that the structures/ organs are homologous. 

Question. Write the technical term that describes each one of the following statements with reference to their evolution :
(i) Microbes developing resistance to antibiotics in a much lesser time scale.
(ii) Resemblance of varieties of placental mammals to corresponding marsupials in Australia.
Answer : (i) Evolution by anthropogenic action i.e. by human activities.
(ii) Adaptive radiation (convergent evolution).

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

Question. (a) Differentiate between analogous and homologous structures.
(b) Select and write analogous structures from the list given below:
(i) Wings of butterfly and birds
(ii) Vertebrate hearts.
(iii) Tendrils of Bougainvillea and Cucurbita
(iv) Tuber of sweet potato and potato.
Answer : (a) Differences between analogous and homologous structures:
Analogous: Anatomically not similar though perform similar functions/ is a result of convergent evolution. 
Homologous: Anatomically similar (but perform different functions)/ is a result of divergent evolution. 
(b) Option (i) Wings of butterfly and birds.
(iv) Tubers of sweet potato and potato

Question. ‘‘Post-industrialization the population of melanised moth increased in England at the expense of white-winged moths.’’ Provide explanations. 
                              ​​​​​​​               ​​​​​​​               OR
How can evolution by natural selection be explained by melanised moths before and after industrialisation in England?
Answer : Pre-Industrialisation had more white winged moth against grey lichens on tree trunk, industrialisation led to deposition of soot and smoke on tree bark, making bark of trees dark, against the dark background. White moth could not survive because they could easily be spotted out and preyed upon by the predators, therefore the melanised moth could camouflage against dark bark and increased in number (through reproduction)/natural selection. 

Question. (i) What are fossils ? How are they an evidence for evolution?
(ii) ‘‘Anthropogenic action can lead to evolution.’’
Explain with the help of an example.
Answer : (i) Fossil-remains / impression of hard parts of life-forms existed in past, preserved in sedimentary rocks, volcanic ash, peat, etc.
They are written documents of evolution.
Study of fossils in different sedimentary layers indicates the geological periods in which they existed and showed that life forms varied over time. This indicates that new forms of life have evolved at different geological times in the history of earth.
(ii) Anthropogenic action i.e. human activities has led to the evolution of a number of new species in a short time scale. This hastens the process of evolution. For example excess use of herbicides and pesticides in crop production has resulted in selection of resistant varieties of pests in a much lesser time scale / use of antibiotics or drugs, against microbes leads to resistant organism in lesser time scale. 

Question. (i) Name the different gases contained in the flask used as an experimental setup by S.L. Miller.
(ii) On the basis of composition of gases in this experiment, what was the condition in the flask ?
(iii) Write the conclusion drawn from this experiment.
Answer : (i) CH₄, NH₃, H₂O and H₂.
(ii) Anaerobic / Anoxygenic.
(iii) Life come from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution. 
Detailed Answer :
(i) Harold Urey and Stanley Miller made electric discharge in a closed flask containing CH₄, NH₃, H₂ and water vapour at 800° C.
(ii) They created a condition similar to that of primitive earth i.e. Anaerobic or anoxygenic.
(iii) Conclusion from the experiment is that life originated from pre-existing non-living organic molecules and that formation of life was preceded by chemical evolution.

Question. What do you infer from the resemblance between flying squirrel and flying phalanges with reference to their evolution. 
Answer : Evolution of marsupial mammals has resulted in flying phalanger, through adaptive radiation.
Evolution of placental mammals has led to the evolution of a flying squirrel (independently). 
The resemblance between the two, proves convergent evolution. 

Question. How do fossils help us in understanding the evolutionary history ? 
Answer : (i) Fossils in different sedimentary layers indicate the period in which they existed. 
(ii) They show that life forms varied over time. 
(iii) New forms of life have arisen at different times in the history of earth. 

Question. Describe the experiment of S.L. Miller on the origin of life. Write the conclusion drawn at the end of the experiment. 
Answer : Miller’s experiment:

The set-up created conditions like that of primitive atmosphere, Electrical discharge with electrodes in closed flask, containing CH₄, NH₃, H₂ , H₂ vapour, observed formation of amino acids.
Conclusion : The first form of life arose through evolutionary forces from non-living molecules / abiogenesis. 

Question. Explain adaptive radiation with the help of a suitable example. 
Answer : The process of evolution that starts from a single point and radiates in different directions is called adaptive radiation e.g. Australian marsupials have evolved from a single ancestor and placental mammals exhibit similarities with their corresponding marsupials such as placental wolves and Tasmanian wolves.

Detailed Answer :
Adaptive radiation is the process of evolution of different species in a given geographical area or starting habitat from a point spreading or radiating to other geographical areas or habitats e.g. members of marsupials, different from each other have evolved from a common ancestral stock and variety of placental mammals exhibit resemblance with corresponding marsupials. Adaptive radiation can be called as the convergent evolution as more than one adaptive radiations have taken place in different habitats of an isolated geographical area.

Question. (i) Explain adaptive radiation with the help of a suitable example.
(ii) Cite an example where more than one adaptive radiation have occurred in an isolated geographical area. Name the type of evolution your example depicts and state why it is so named.
Answer : (i) Adaptive radiation is the process of evolution of different species in a given geographical area from a point and spreading or radiating to other geographical area or habitats. For example: Drawin’s finches / black birds (on Galapagos islands) evolved from original seed eating features into insectivorous and vegetarian features in different habitat / islands. 
(ii) Number of Australian marsupials and placental mammals, different from each other have evolved from an ancestral stock within Australian island continent. 
This is a type of convergent evolution, because more than one adaptive radiation occurred in isolated geographical area. 
Detailed Answer :
(i) Darwin during his journey to Galapagos Islands observed that there were many varieties of small black birds later called Darwin’s finches.
(a) All the varieties he conjectured, evolved on the island itself.
(b) 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.
(ii) E.g. Australian marsupials and placental mammals. Number of marsupials, different from each other evolved from an ancestral stock, but all within the Australian island continent.
Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be ‘similar’ to a corresponding marsupial (e.g., Placental wolf and Tasmanian wolf).
Convergent evolution : This is because, more than one adaptive radiation has occurred in isolated geographical area. 

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 categorized as ? 
Answer : The forelimbs of frog, lizard, pigeon, bat, whale and horse have the same basic structural plan as human hand. In each case, the forelimb consists of an upper arm, forearm, wrist, palm and fingers.
The upper arm is made up of humerus, forearm is composed of radio-ulna, the wrist consists of carpals and the palm contains metacarpals and digits. The forelimbs of all these vertebrates are categorized as homologous organs because these are similar in structure and arrangements but are different in shape and function because they developed along different direction due to adaptation to different needs. 

Question. What is adaptive radiation ? When an adaptive radiation be referred to as convergent evolution? Give an example ?. 
Answer : The process of evolution of different species from one species in a given geographical area starting from a point and radiating or spreading to other geographical areas or new habitats is called adaptive radiation. This is called as divergent evolution as this involves the formation of different functional forms of basic similar structures e.g. Darwin’s finches and Australian marsupials. However when more than one adaptive radiation appeared to have taken place in different habitats of an isolated geographical area, the adaptive radiation can be referred to as convergent evolution. This involves the development of similar adaptive functional structures in unrelated groups of organisms e.g. Australian marsupials and placental mammals. 

Question. Name the scientist who influenced Darwin and how? 
Answer : Darwin was influenced by Thomas Malthus and his book ‘‘An essay on the principles of population’’ in which he discussed that there are ‘positive checks’ that control geometrically growing population. The work of Malthus on human population growth in fact influenced him. 

Question. State the hypothesis proposed by Oparin and Haldane. How was it experimentally proved by
S.L. Miller ? Explain.
Answer : The first form of life could have come from pre-existing non living organic molecules (RNA, protein etc.), and that formation of life was preceded by chemical evolution or formation of diverse organic molecules from inorganic constituents, the condition on earth were high temperature (Volcanic storms), reducing atmosphere (containing CH₄, NH₃, etc.), Miller in his experiment created electric discharge in a closed flask, containing CH₄, H₂, NH₃ and water vapour at 800° C, and observed the formation of amino acids / organic compounds, which supported chemical evolution. 
Detailed Answer :
Oparin and Haldane proposed the theory of chemical evolution of life. It states that, the first form of life was originated from non-living inorganic and organic molecules such as CH₄, NH₃, H₂O, sugar, proteins, nucleic acids, etc. Harold Urey and Stanley Miller conducted an experiment to prove this theory. They created a condition similar to that of primitive earth. They made electric discharge in a closed flask containing CH₄, NH₃, H₂ and water vapour at 800° C and observed the formation of amino acids, which supported chemical evolution.

Question. (i) How does the study of fossils help to understand evolution.
(ii) How did S.L. Miller provide an experimental evidence in favour of Oparin and Haldane’s hypothesis? Explain.
Answer : (i) The fossils are the written documents of evolution. Study of fossils in different sedimentary layers indicates the geological period in which they existed and showed that life forms varied over time. This indicates that various forms of life have evolved at different geologic times and hence new forms of life similar to modern organisms have arisen at different times in history of earth and from the study of fossil record. Thus, it has been concluded that evolution has taken place from simple to complex in a gradual manner.
(ii) Oparin and Haldane gave the hypothesis of chemical evolution of life. They suggested that life could have come from pre-existing nonliving organic molecules and that the formation of life was preceded by chemical evolution.
Miller created electric discharge in a closed flask, containing methane, hydrogen, ammonia and water vapour at 800°C and thus created conditions similar to prehistoric earth in the laboratory. He observed formation of amino acids thus supporting that life originated from pre-existing, non-living organic molecules.

Question. (i) Explain the observations and the conclusion drawn by Darwin during his visit to Galapagos islands.
(ii) Write the two key concepts of Darwin’s theory of natural selection.
Answer : (i) Small black birds-Darwin’s finches-Many varieties of finches in the same island, which he conjectured evolved in the island itself, Seed eating-altered beaks arose-insectivorous. Thus, the process of evolution of different species in a given geographical area starting from a point and radiating to other areas of geographical habitats is Adaptive Radiation. 
(ii) Branching descent, struggle for existence, competition, survival of fittest.
Detailed Answer :
(i) (a) During his visit to Galapagos islands Darwin observed a great diversity of small black birds called Darwin’s Finches. He described Galapagos islands as the living laboratory of evolution. He observed that there were 13 species of finches differing from each other as well as from main land finches in their size, beaks and food habits. From these observations, Darwin concluded that from original seed eating birds many different varieties with altered beaks have evolved such as finches, vegetarian finches etc. He further concluded that after originating from common ancestral seed bearing stock the finches must have spread or radiated to different geographical areas or habitats and undergone adaptive changes in their beaks according to food habits to become vegetarian or insectivorous. This process of evolution of different species of Darwin’s finches in a given geographical area starting from a point and radiating or spreading to other areas of geographical habitats is called adaptive radiation.
(ii) Two key concepts of Darwin’s theory of natural selection
(a) Branching descent (adaptive radiation).
(b) Struggle for existence and competition and
(c) Survival of the fittest.

Question. How they are considered as an evidence of evolution.
Answer : Analogy and homology of structures indicate the evidences of evolution from comparative study of morphology and anatomy of form, structure, relative position of different organs and their functions. Analogy indicates that similar environmental conditions and habitat result in the selection of similar adaptive features in different groups of organisms towards the similar function. This shows the evolution of similar functional structures from unrelated organs. This is the result of convergent evolution.
Homology includes the organs having similar structure origin and development, developed to have different forms so as to perform different functions in different groups of organisms.
This phenomenon of producing functionally different forms from structurally similar organs is the result of divergent evolution. It indicates towards the common ancestry.