Evolution Questions Class 12 Biology

ICSE Class 12 Biology

Origin of Life on Earth and Various Related Evidences

Very Short Answer Type Questions

Question. State a reason for the increased population of dark coloured moths with the loss of lichens (on tree barks) during industrialization period in England.
Answer : During industrialization period in England the lichens got wiped out due to air pollution and tree trunks became dark due to industrial smoke so that the dark coloured moths could camouflage in the dark background without any risk of predation. Thus, they escaped predation, survived and therefore increased in population, whereas white winged moth did not survive due to predation and industrial pollution.

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.

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.

Question. 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 ?
Answer : (i) The wings of a bird and the wings of a cockroach are analogous organs because these organs are used for flying.
(ii) They are different in structure. Each has evolved from a separate ancestral population as a means of more efficient mode of locomotion.

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

Question. State the significance of the study of fossils in evolution.
Answer : Fossils represent extinct organisms. Fossils show life forms restricted to certain geological time spans existing in the past. Fossils show ancestry of present day organisms. Some of the fossils are the connecting link between two groups of organisms.

Question. Name the scientist who disproved the spontaneous generation theory. 
Answer :
Louis Pasteur disproved the theory of spontaneous generation. He proved biogenesis

Question. “Sweet potato tubers and potato tubers are the result of convergent evolution.” Justify the statement.
Answer : Sweet potato tuber is a root modification and potato tuber is a stem modification but they show convergent evolution because both of them are unrelated and perform the functions similar like storage of food and vegetative reproduction.

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. 

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. 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. Name the type of evolution that has resulted in the development of structures like wings of butterfly and bird. What are such structures called.
Answer :
Convergent evolution. Such structures are called analogous structures.\

Short Answer Type Questions – l

Question. Explain with the help of an example the type of evolution homology is based on ?
Answer : Homology is based on divergent evolution. These have similar anatomical structure but perform different function.
Example : Thorns of Bougainvillea and tendrils of Cucurbita/Forelimbs of human and horse (any other appropriate example).

Question. State the evolutionary relationship giving reasons between the thorn of Bougainvillea and tendril of cucurbit.
Answer : Divergent evolution/Homologous organs Similar in origin but perform different function.

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. 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 Cucurbita.
(iv) Forelimbs of Bat and Whale.
Answer : (i) & (ii) Analogous.
(iii) & (iv) Homologous. 

Question. Mention the contribution of S.L. Miller’s experiments on Origin of Life.
Answer : S.L. Miller created an environment in a laboratory similar to the one that existed before life originated. In a closed flask containing CH4, H2, NH3 and water vapour at 800°C, electric discharge was created.
The conditions were similar to those in primitive atmosphere. After a week, they observed presence of amino acids and complex molecules like sugars, nitrogen bases, pigments and fats in the flask. This provided experimental evidence for the theory of chemical origin. 

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. 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. 

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

Answer : Name of the scientist is S.L. Miller.
Purpose of ‘a’ is to supply electric discharge as it is a substitute of thundering.
Conclusion : Life originates from pre-existing life. It proved the chemical evolution of life.

Question. List two main propositions of Oparin & Haldane.
Answer : (i) Chemical evolution from inorganic molecules to organic molecules.
(ii) First life formed by assembly and interaction of organic molecules.

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. How do Darwin’s finches illustrate adaptive radiation ? 
Answer : Original stock of seed-eating finches migrated to different habitats (of Galapagos Islands), adapted to different feeding methods by altered beak structure and evolved into different types of finches.

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. 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. 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. Divergent evolution leads to homologous structures. Explain with the help of an example.
Answer : Development of different functional structures from a common ancestral form due to their migration to different habitats and adaptation to new requirements is called divergent or adaptive radiation.
For example : Darwin’s finches of Galapagos Islands had common ancestors but now have different types of modified beaks according to their food habits. 

Question. How does palaeontological evidence support the evolution of life on earth.
Answer : Fossils are the remains of life forms of the part preserved in the rock. The study of fossils is called paleontology. Rock sediments of different
ages contain fossils of different types. Early rocks contain fossils of simple organisms while recent rocks contain fossils of complex organisms and
some contain extinct organisms. Study of fossils in different sedimentary layers indicate the geological period in which they existed and accordingly also
indicate the evolutionary changes in the organisms. Hence, new forms of life evolved at different geologic times in the history of earth.

Short Answer Type Questions – ll

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

Question. How do homologous organs represent divergent evolution ? Explain with the help of a suitable example
Answer :
Organs with similar structure / same ancestry / anatomically same / same origin developed along different directions due to adaptation / different needs to perform different functions. 
For example: The fore limbs of some animals (Vertebrates) like whales, bats, cheetah and human have similar anatomical structure (i.e. humerus, radius, ulna, carpals, metacarpals and phalanges) develop differently to meet different needs / to perform different functions.
Detailed AnswerDifference between divergent and convergent evolution :

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.

Question. Differentiate between homology and analogy.
Give one example of each.
Answer :

Question. ‘‘Post-industrialization the population of melanised moth increased in England at the expense of white-winged moths.’’ Provide explanations. 
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. Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life. 
Answer : Two pre sterilised flasks with killed yeast, one sealed, other open to air, differential growth of life in two flasks / life was found only in open flask. The following diagram can be considered in lieu of above explanation, life comes from pre-existing life (it came from air entering the flask) / proved the theory of biogenesis.

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. How did industrialization play a role in Natural selection of light and dark coloured moth in England ?
Explain the increase in the numbers of melanic (dark winged) moths in the urban areas of postindustrialization period in England.
How does industrial melanism support Darwin’s theory of Natural Selection ? Explain
Answer : Industrial melanism is an example of natural selection. Before industrialisation, there were more white winged moth on trees than dark winged.
After industrialisation, due to industrial smoke and soot, tree trunks became dark because dark coloured moth survived by hiding among dark
coloured bark and the light coloured moth were easily spotted and picked by predators. Under this condition the white winged moths did not survive, due to predation. Dark coloured moth survive / able to camouflage to survive. This supports the principle of natural selection and supports the fact that species that can better adapt are fit and survive and increase in population size.

Question. What type of organs- eye of an Octopus and that of a human called ? Give another example from the animal group and one from the plants of such organs Name and explain the evolutionary process they exhibit.
Answer : Analogous 
(i) Flippers of Penguins & Dolphins / Eye of octopus and mammals.
(Any other appropriate & correct example)
(ii) Sweet potato (root modification) and potato (stem modification).
They are anatomically dissimilar structure though they perform similar function, convergent 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. (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. Refer to the figure given below and answer the questions that follow : Wolf Tasmanian Wolf
(i) Explain the process by which Tasmanian wolf evolved.
(ii) Name the process that has resulted in evolution of wolf and another similar animal such as Tasmanian wolf.
(iii) Compare and contrast the two animals shown?

Answer : (i) Adaptive radiation : The process of evolution of different species in a given geographical area starting from a point and radiating to other areas of geography (habitats).
(ii) Convergent evolution (Adaptive convergence): formation of functionally similar structures independently by unrelated organisms.
(iii) Wolf is a placental mammal whereas Tasmanian wolf is a marsupial mammal.

Question. How does the study of fossils support evolution ? Explain. 
Answer : Fossils are remains / hard parts of life forms, found in sedimentary rocks, some of them appear similar to modern organisms / some represent extinct organisms, study of fossils in different sedimentary layers indicates the geological period in which they existed (provide palaeontological evidence).

Question. State the contribution of Louis Pasteur in understanding the origin of life on earth. Explain the procedure that he followed to arrive at his conclusion.
Answer : Pasteur in his experiment took a flask containing sugar solution and added yeast to it, then boiled the contents of the flask so that yeast got killed.
In pre-sterilized sealed flask (open to air) life comes from pre existing life, new living organisms arose in presence of killed yeast.

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. 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.

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.

Question. With the help of any two suitable examples explain the effect of anthropogenic actions on organic evolution.
Answer : New species evolve in a short time scale of months or years due to anthropogenic actions or human activities. This hastens the evolutionary process. 
For example,
(i) During post industrialisation period in England, the tree trunks were covered by dust, coal particles and thus became dark. On such trunks, white moths could be easily picked up leaving the dark-peppered moths.
(ii) Due to excessive use of antibiotics or herbicides, new resistant varieties of organisms appeared. These resistant varieties got selected over the non-resistant varieties. 

Question. State the theory of Biogenesis. How does Miller’s experiment support this theory ?
(i) Explain the theory of biogenesis.
(ii) How did Miller demonstrate experimentally the chemical evolution that happened three billion years ago ?
Answer : Theory of Biogenesis : A living organism arises from another living organism.
Miller’s experiment : An electric discharge was created in a closed flask containing CH4, H2, NH3, and water vapour at 800° C, thus creating condition of early earth with reducing environment, high energy radiations and high temperature in the laboratory. This resulted in the formation of amino acids, supports chemical evolution of life.
// Miller’s experiment does not support theory of Biogenesis it supports chemical evolution of life.

Question. A student was simulating Urey and Miller’s experiment to prove the origin of life. The set up used by the student is given

(i) Find out the reasons why he could not get desired results?
(ii) What conclusion was drawn by Urey and Miller hrough this experiment ?
(iii) Compare the conclusion drawn with the theory of spontaneous generation.
Answer : (i) He could not get desired results because :
(a) O2 was used instead of H2.
(b) Temperature maintained was 80°C instead of 800°C. 
(ii) It was concluded that life could have come from pre-existing non-living organic molecules and their formation was preceded by chemical evolution.
(iii) They observed formation of amino acids when in a closed flask CH4, H2, NH3 and water vapour were heated at 800°C in presence of electric discharge. Analysis of meteorite content also reveals similar compounds indicating that similar process are occurring elsewhere in space / chemical evolution. Urey & Miller proved that life originated abiogenetically whereas theory of spontaneous generation emphasized that units of life called spores were transferred to different planets including earth.

Question. Excessive and continuous use of pesticides lead in evolution of some new species of pests. Explain what must have led to this. What is this type of evolution called ?
Answer : 
Excessive use of pesticides has resulted in selection of resistant varieties in a much lesser time scale, as evolution is stochastic process based on chance events in nature and chance mutation in organism. Evolution by anthropogenic action.

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.

Long Answer Type Questions

Question. (i) List any four evidences of evolution.
(ii) Explain any one of the evidences that helps to understand the concept of evolution.
Answer : (i) Four evidences = Fossils / comparative anatomy / homologous organs / Analogous organs / Biochemical evidences / embryological evidences.
(ii) Any one evidence explained 
Definition / concept
How it explains evolution.

Question. (i) What was proposed by Oparin and Haldane on origin of life ? How did S.L. Miller’s experiment support their proposal ?
(ii) Which human chromosome has (1) maximum number of genes, and which one has (2) fewest genes ?
(iii) Write the scientific importance of single nucleotide polymorphism identified in human genome.
Answer : (i) Oparin and Haldane believed in the chemical evolution of life. They proposed that the first form of life could have come from pre – existing non-organic molecules. S.L. Miller created electric discharge in a closed flask containing CH4, H2, NH3 and water vapour at 800° C, thus creating the condition of early earth with reducing environment, high energy radiation and high temperature. This resulted in the formation of amino acids Miller’s experiment thus supports the chemical evolution of organic molecules from the inorganic ones, a condition being the basis requirement conducive to the formation of early life. 
(ii) Chromosome 1, Y 
(iii) It help to find chromosomal locations for disease, associated sequences and tracing human history. 

Question. How did Darwin explain adaptive radiation ?
Give another example of animals exhibiting adaptive radiation.
Answer : The process of evolution of various species in certain geographical area beginning from a point and spreading or radiating to other geographical
areas or habitats is remains as adaptive radiation. One of the best example of this phenomenon is that of Darwin’s Finches.
Darwin observed many varieties of finches on the same island all of which have evolved on the island itself from original seed eating features.
This has led to many other forms with altered beaks, 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 is called adaptive radiation.
Another example = Australian Marsupials.

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.

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. 

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. Evolution is a change in gene frequencies in a population in response to changes in the environment in a time scale of years and not centuries. Justify this statement with references to DDT. How does the theory of Hugo de Vries support this.
Answer : The use of DDT for the first time resulted in the death of maximum number of mosquitoes but few survived. Later on it was found that mosquitoes continue to survive and reproduce even in the presence of DDT. It is because the sustained use of DDT made the mosquitoes resistant to DDT within a few years due to variation and change in gene frequencies in their population in relation to changes in environment within a time span of few years only. According to Hugo de Vries, the evolution is caused by a single step large mutation arising out suddenly in a population.

Evolutionary Theories, It’s Mechanism and Evolution of Man

Question. Name the common ancestor of the great apes and man.
Answer :

Question. What role does an individual organism play as per Darwin’s theory of natural selection ?
Answer :
Individual with reproductive fitness passes on the useful gene to the next generation. 

Question. According to De-Vries what is saltation?
What is ‘Saltation’ according to De Vries?
Answer :
Saltation is a single step large mutation which brings major change as speciation.

Question. Write the basis of origin of variations in organisms as described by Hugo de Vries.
Answer :
Saltations (Mutation), large differences arising out all of a sudden in a population.

Question. State the significance of coelacanth in evolution.
Answer :
Coelacanth is a special type of fish called lobfin caught in S. Africa in 1938. It is significant in evolution because it is a missing link between fishes and the amphibians. They evolved into the first amphibians that lived on both land & water.

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 :
(i) Pre-historic cave art.
(ii) Agriculture / Human Settlement. 

Question. Name the common ancestor of great apes and man.
Answer :
Dryopithecus africanus.

Question. If the frequency of one allele is ‘p’ and for another, it is ‘q’ for one gene, what will be the formula to calculate allele frequency in future generations according to Hardy-Weinberg genetic equilibrium ?
Answer :
The formula to calculate allele frequency is :
(p + q)2 = p2 + 2pq + q2 = 1

Question. Write the names of the following:
(a) A 1.5 mya primate that was ape-like.
(b) A 2 mya primate that lived in East African grasslands.
Answer :
(a) Dryopithecus. ½
(b) Australopithecines / Australopithecus / Homo habilis. 

Question. Rearrange the following in increasing order of evolution.
Gnetales, Ferns, Zosterophyllum, Ginkgo.
Answer :
Zosterophyllum → Ferns → Ginkgo → Gnetales.

Question. List the two characteristics of mutation that help in explaining evolution.
Answer :
(i) Mutation are random and inheritable.
(ii) Same type of mutations may occur in a number of individuals of same species. 


Study the ladder of human evolution given above and answer the following questions.
(i) Where did Australopithecus evolve?
(ii) Write scientific name of Java man.

Answer : (i) East Africa.
(ii) Homo erectus.

Short Answer Type Questions – l

Question. Name the first human like hominid. Mention his food habit and brain capacity.
Answer :
Homo habilis were first human like hominid. They probably did not eat meat/vegetarian, and their brain capacities were between 650-800 cc. 

Question. Describe the mechanism of evolution as explained by Hugo de Vries.
Answer :
While working on evening primrose, Hugo de Vries put forward the idea of mutation, which he described as the large change arising out all of a sudden in a population. It is believed that evolution is not due to minor heritable continuous variations as proposed by Darwin but this is due to mutation which cause evolution. According to Darwin, the evolution is a gradual and slow process but de- Vries believed that it is due to saltation, single step large change called mutation and is a discontinuous process. It brings about speciation.

Question. Mention the evolutionary significance of the following organisms :
(i) Shrews
(ii) Lobefins
(iii) Homo habilis
(iv) Homo erectus
Answer :
(i) First mammals
(ii) First amphibians (lived both on land and in water) / fish with stout and strong fins which could move on land and go back to water.
(iii) First human like being / hominid / brain capacity from 650 – 800 cc / did not eat meat. 
(iv) Large brain around 900 cc / eat meat. 

Short Answer Type Questions – ll

Question. Explain the interpretation of Charles Darwin when he observed a variety of small black birds on Galapagos Island.
Answer :
Charles Darwin observed an amazing variety of small black birds called Darwin’s finches in the same island. All the varieties evolved on the island itself from ancestral stock and have radiated to different habitats where they have undergone adaptive changes. Darwin interpreted the formation of a number of divergent species from a common ancestral stock with new species adapting different habitats as adaptive radiation resulting into the divergent evolution.
According to Darwin this evolution was also based on available resources of food and space and on this basis therefore by observing their characteristics on the Galapagos islands, he proposed his famous theory known as the ‘theory of natural selection’. The main postulates of this theory are as follows :
(i) All organisms possess an enormous power of fertility.
(ii) There is a struggle for the existence within a species as well as between two different species for food, space and resources.
(iii) Nature will favour the survival of the fittest.
(iv) Darwin believed that variations ultimately lead to the formation of new species.

Question. (i) Rearrange the following in an ascending order of evolutionary tree : reptiles, salamander, lobfins, frogs.
(ii) Name two reproductive characters that probably make reptiles more successful than amphibians.
Answer : (i) Lobefins, frogs, salamanders and reptile.
(ii) Two reproductive characters that made reptiles more successful than amphibians are :
(a) Reptiles lay eggs on land.
(b) Reptiles lay thick shelled egg which do not get dry up in sun shine unlike those of amphibians.

Question. Compare and contrast the theories of evolution proposed by Darwin and Hugo De Vries.
Answer :

Question. Describe the three different ways by which Natural selection can affect the frequency of a heritable traits in population.
Answer :
(i) Stabilization, in which more individual acquire average character value i.e., medium sized individuals. 
(ii) Directional, more individuals acquire value other than the average character value.
(iii) Disruptive, more individuals acquire peripheral character value at both ends of distribution curve. Consequently the original population is disrupted into two or more separate groups that later evolved into new species.

Question. How can Hardy-Weinberg equilibrium be affected?
Explain giving three reasons.
Answer : (i) Gene migration / gene flow : When migration of a section of population occurs to another place and gene frequencies change in the original as well as in the new population.
(ii) Genetic drift : If the same change occurs by chance / new genes / alleles are added to the new population and these are lost from the old population.
(iii) Mutation : Pre existing advantageous mutations when selected will result in new phenotypes.
(iv) Genetic recombination : Variation in characteristics will be there because of genetic recombination during meiosis and also due to random fusion of gametes.
(v) Natural selection : Heritable variations enabling better survival enabled organisms to reproduce and leave greater number of progeny.

Question. What does Hardy-Weinberg principle of equilibrium indicate? List any two factors that could alter the alteration. What would such an alteration lead to ?
Answer :
(i) Allele frequencies are stable and constant from generation to generation / the gene pool (total genes and their alleles in a population) remains a constant / sum total of all allelic frequencies is one.
Hence, p2 + 2pq + q2 = 1 (where p and q represent the frequencies of gene A and allele a).
Factors : Gene migration, gene flow, genetic drift, mutation, genetic recombination, natural selection.
(ii) Such an alteration causes variations at the genetic level and thus leads to evolution.

Question. With the help of an algebraic equation, how did Hardy-Weinberg explain that in a given population the frequency of occurrence of alleles of a gene is supposed to remain the same through generations ?
Answer : In a population of diploid organisms If frequency of allele A = p and frequency of allele a = q
Genotype frequency under random mating are
AA = p2 (for the AA homozygotes)
aa = q2 (for the aa homozygotes)
Aa = 2pq (for the Aa heterozygotes)
(In absence of selection, mutation, genetic drift or other forces, allelic frequency p and q are constant through generation).
Therefore, p2 + 2pq + q2 = 1 

Question. (i) State Hardy-Weinberg principle. Name any two factors which affect it.
(ii) Draw a graph to show that natural selection leads to directional change.
Answer :
(i) Hardy-Weinberg principle states that the total genes and their alleles in a population remains constant i.e. allelic frequencies in a population are stable and constant from generation to generation. Gene flow, genetic drift, mutation, genetic recombination, natural selection.

Question. What does the following equation represent ?
p2 + 2pq + q2 = 1
p2 + 2pq + q2 = 1. Explain this algebraic equation on the basis of Hardy Weinberg’s principle.
Answer :
The equation p2 + q2 + 2pq = 1 represents the
genotypic frequencies of a population, when it is in Hardy-Weinberg equilibrium.
According to this law, the frequency of occurrence of alleles of a gene in a population remains constant through generations unless disturbances, such as mutation and non-random mating are introduced.
Individual frequencies are represented as p and q such as in diploid where p and q represent the frequency of allele A and a respectively. The sum total of allelic frequencies is
The frequency of genotypes, AA is p2, that of aa is q2 and that of Aa is 2pq.
Hence p2 + 2pq + q2 = 1 which is expansion of binomial expression (p + q)2. When frequency measured differs from expected values the difference indicates the extent of evolutionary change.

Question. Fitness is the end result of the ability to adapt and get selected by nature. Explain with suitable example.
Answer : Industrial Melanism : Before industrialisation started in England it was observed, there were more white – winged peppered moth on trees than dark winged moth but after industrialisation, there were more dark – winged moths in the same area, predators spot a moth against a contrasting background, post industrialisation the tree trunk became dark due to industrial smoke and soot, Under this condition the white- winged moth did not survive due to predators, but the dark-winged moth managed to survive.
Note : Any other example explained under the following heads in the text book – fitness, selection and adaptation.

Question. When does a species become founders to cause founder effect ?
How does a population become founders’ of a new species.
Answer : When a few members or a small group of members from a certain population invades a new geographical region, they may have a different type of or changed allele frequencies from that of the original drifted population, they become the founders of new species and the effect is called as the founder’s effects.

Question. Write in what context did Darwin use that terms ‘fitness‘, ‘survival‘ and ‘selection‘ while elaborating the mechanism of evolution. 
Answer :
Fitness refers to reproductive fitness (will leave more progeny) – more survival and hence selected by nature – natural selection

Question. (i) How does the Hardy – Weinberg’s expression
(p2 + 2pq + q2 = 1) explain that genetic equilibrium is maintained in a population ?
(ii) List any two factors that can disturb the genetic equilibrium.
Answer : (i) The gene pool i.e. the total genes and their alleles in a population tend to remain constant, this is called genetic equilibrium.
Sum total of all allelic frequencies is 1. Individual frequencies can be named p, q, etc. In a diploid, p and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p2.
This is simply stated in another way i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities i.e. p2 . Similarly of aa is q2, of Aa 2pq. Hence, p2 + 2pq + q2 = 1. When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change. Disturbance in genetic equilibrium or Hardy – Weinberg equilibrium i.e. change of frequency of alleles in a population would then be interpreted as resulting in evolution.
(ii) Gene migration / gene flow / gene drift / mutation / genetic recombination / natural selection.

Question. Branching descent and natural selection are the two key concepts of Darwinian Theory of
Evolution. Explain each concept with the help of a suitable example. 
Answer : Branching descent : Different species descending from the common ancestor – get adapted in different habitats.
E.g. Darwin finches – varieties of finches arose from grain eaters / Australian marsupials – evolved from common marsupial. Natural selection : A process in which heritable variations enable better survival of a species to reproduce in large number. e.g. White moth surviving before the industrial revolution and black moth surviving after industrial revolution / Long necked giraffe survived / DDT resistant mosquito survive. 

Question. Name the ancestors of man based on the features given below—
(i) Human like, meat eater with 900 cc brain, lived in Java.
(ii) More human with brain size 1400 cc, lived in central Asia, used hides & buried their dead.
(iii) Human like, vegetarian, with brain capacity between 650 cc & 800 cc.
(iv) Man like primate, that existed about 15 mya. Fossils found in Tanzania.
Answer : (i) Homo erectus
(ii) Homo sapiens neanderthalensis
(iii) Homo habilis
(iv) Australopithecus africans/Ramapithecus

Long Answer Type Questions

Question. (i) Explain Darwinian theory of evolution with the help of one suitable example. State the two key concepts of the theory.
(ii) Mention any three characteristics of Neanderthal man that lived in near east and central Asia.
Answer : (i) Darwinian theory of evolution :
(a) According to Darwin, evolution took place by natural selection.
(b) The number of life forms depends upon the life span of the organisms and their ability to multiply.
(c) Another aspect of natural selection is the survival of the fittest, in which nature selects the individuals that are most fit to adapt to their environment.
(d) Darwin also observed that variations are inheritable and the species that fit to survive the most, leaves more offsprings. Hence, the population’s characteristics change, giving rise to the evolution of new life forms.
An example of such selection is the antibiotic resistance in bacteria. When a bacterial population was grown on an agar plate
containing antibiotic penicillin, the colonies that were sensitive to penicillin died, whereas one or a few bacterial colonies that were resistant to penicillin survived.
This is because these bacteria had undergone chance mutation, which resulted in the evolution of a gene that made them resistant to penicillin drug. Hence the resistant bacteria multiplied quickly compared with the non-resistant (sensitive) bacteria, thereby increasing their number. Hence, the advantage of an organism over the other helps in the struggle for existence.
The two key concepts of the theory are :
(1) Branching descent : According to this concept, various species have come into existence from a common ancestor.
(2) Natural selection : According to this concept, nature selects the individuals that are most fit to adapt to their environment.
(ii) Characteristics of Neanderthal man :
(a) They possess a brain capacity of 1300 – 1600 cc.
(b) They were short but very strong with outward-curved thigh bones.
(c) They used hides to protect their body. They buried the dead.

Question. (i) How did Darwin explain adaptive radiation ?
Give another example exhibiting adaptive radiation.
(ii) Name the scientist who influenced Darwin and how ?
Answer : Darwin explained the phenomenon of adaptive radiation on the basis of his investigation on fauna of Galapogas islands. Finches of Galapogas island offer the best example of adaptive radiation.
(i) During his journey, Darwin went to Galapogas island and observed that there were many varieties of finches in the same island. They varied from normal seed-eating ones to those that ate insects. Another example of adaptive radiation is evolution of the Australian marsupials from a single ancestor. 
(ii) Work of Thomas Malthus influenced Darwin.
He gave an idea about population growth and food availability. He said that present growth of human population is more than what food and other resources can sustain. This means that many people would die of starvation to level out the population. His views gave the Darwin the idea about “survival of fittest”. 

Question. (i) Describe Hardy – Weinberg Principle.
(ii) List any four factors which affect genetic equilibrium.
(iii) Describe founder effect.
Answer :
(i) Allele frequencies in a population are stable and constant / gene pool, total genes and their alleles in a population remain constant from generation to generation and maintain genetic equilibrium.
(ii) Factors affecting genetic equilibrium are —
(a) Gene migration / gene flow.
(b) Genetic drift.
(c) Mutation.
(d) Genetic recombination.
(e) Natural selection. (Any four)
(iii) (a) Change in allele frequency.
(b) New genes develop, old genes are lost.
(c) Migration.
(d) Drift.
(e) New species.
When section of population gets separated due to migration or genetic drift, gene frequencies changes, sometimes this change in allele frequency is different in the new population so that they becomes new species, this is called founder effect.

Question. (i) How did Darwin explain adaptive radiation by taking an example of finches ?
(ii) How did Darwin’s view on evolution differ from that of de-Vries ?
Answer : (i) Darwin conjectured that the Darwin’s finches evolved on the island itself.
There were seed-eating finches and other finches with altered beaks arose allowing different types of food eating habits like insectivorous and vegetarian finches. 
This process of evolution of different species in a given geographical area starting from a point and radiating to other areas of (geographical) habitats is called adaptive radiation.

Question. How does the process of natural selection affect Hardy–Weinberg equilibrium ? Explain. List the other four factors that disturb the equilibrium.
(i) Write Hardy–Weinberg principle.
(ii) Explain the three different ways the natural selection can affect the frequency of a heritable trait in a population shown in the graph given below.

Answer : (i) Hardy–Weinberg’s principle says that allele frequencies in a population are stable and constant from generation to generation. The
gene pool remains constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1. Individual frequencies e.g. can be named p, q etc. Natural selection disturbs the allelic frequencies. Through natural selection either the frequency of p increases or the frequency of q it disturbs the natural frequency. In a diploid, p and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p2.
This is simply stated in another ways i.e. the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is the product of the probabilities.
Hence, p2 + 2pq + p2 = 1.
The factors that affect the Hardy–weinberg’s equilibrium are : Migration, Gene flow, Genetic drift, mutation and genetic recombination.
(ii) Variation due to mutation or recombination during gametogenesis or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation. Natural selection can lead to stabilization (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).

Question. (i) How do the observations made during moth collection in pre and post-industrialized era in England support evolution by Natural Selection ?
(ii) Explain the phenomenon that is well represented by Darwin’s finches other than natural selection.
Taking an example of white-winged moths and dark-winged moths of England in pre and post industrialised era, explain evolution by natural selection.
Answer :
(i) (a) Before industrialisation white coloured lichen covered the trees in which white winged moths camouflaged themselves from predators.
(b) More white winged moths existed on trees than dark winged or melanised moths.
(c) After industrialisation there were more dark winged moths in the same area i.e., proportion was reversed,
(d) Predators would spot a moth easily against a contrasting background.
(e) During post industrialisation tree trunks became dark due to industrial smoke and soot.
(f) White winged moth did not survive due to detection by predators whereas dark winged survived.
(ii) 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 become insectivorous and vegetarian finches. 

Question. (i) Name the primates that lived about 15 million years ago. List their characteristic features.
(ii) (a) Where was the first man-like animal found ?
(b) Write the order in which Neanderthals, Homohabilis and Homo erectus appeared on earth. Statethe brain capacity of each one of them.
(c) When did modern Homo sapiens appear on thisplanet ? 
Answer :
(i) Dryopithecus, Ramapithecus.
They were hairy.
Dryopithecus is ape like Gorillas and Chimpanzees.
Ramapithecus more man like.
(ii) (a) Ethiopia / Tanzania / Eastern Africa.
(b) Order of appearance from earliest to the latest = Homo habilis, Homo erectus, Neanderthals.
Cranial capacity = Homo habilis = 650 – 800 cc,
Homo erectus = 900 cc, Neanderthals = 1400 cc. 
(c) During ice age / 75000 – 10000 years ago.

Question. Study the schematic representation of evolutionary history of plant forms given below and mention.
(i) The plant form ferns and conifers are most related to
(ii) The nearest ancestors of flowering plants.
(iii) The most primitive group of flowering plants.
(iv) Common ancestry of psilophyton provides to.
(v) Common ancestors of psilophyton and seed ferns.
(vi) Common ancestors of mosses and tracheophytes.
Answer :
(i) Psilophyton.
(ii) Seed ferns.
(iii) Chlorophyte ancestor.
(iv) Ferns, conifers & seed ferns.
(v) Tracheophyte ancestor.
(vi) Chlorophyte ancestor.

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