CBSE Class 12 Biology Evolution Assignment Set B

POINTS TO REMEMBER

Artificial Selection : It is the process carried out by man to select better breeds of plants and aminals.
Bio-geography : The study of patterns of distribution of plants and aminals in different parts of earth.
Founders Effect : A genetic drift in human population where a population in a new settlement have different gene frequency from that of the parent population. The original drifted population said to be founder.
Gene Pool : Sum total of all the genes in a population.
Genetic Drift : Chance elimination of genes of certain traits from a population due to migration or death.
Panspermia : Units of life in the form of so called spores, which were transferred to earth from outer space (as believed by some scientists).
Saltation : Single step large mutations.
Speciation : It is the formation of new species from the pre-existing ones. Organic (Biological) Evolution : Changes in the characteristics/features of organisms or groups of such populations over a number of generations.
Homologous organs : These have same basic structure and embryonic origin but perform different functions in different species.
Analogous organs : These organs are different in their basic structure and embryonic origin but perform similar functions.
Human Evolution : Ramapithecus ® Australopithecus ® Homo habilis ® Homo erectus ® Homo sapiens ® Homo sapiens sapiens. The Theories of Origin of Life
1. Theory of Special Creation : According to this theory God has created life within 6 days.

Long Answer Type Questions

Question. Name the law that states that the sum of allelic frequencies in a population remains constant. What are the five factors that influence these values?
Answer : Hardy-Weinberg Principle states that the sum of allelic frequencies in a population is stable and is constant from generation to generation, i.e., the gene pool (total genes and their alleles in a population remains constant. This is called genetic equilibrium. The sum total of all the allelic frequencies is Five factors that influence these values are
(i) Gene Migration or Gene Flow When migration of a section of population to another place occurs, gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population. There would be gene flow if this gene migration, happens multiple times.
(ii) Genetic Drift It refers to the elimination of the genes of certain traits when a section of population migrates or dies of natural calamity. It is an evolutionary force operating in small populations whereby gene frequency changes by chance leadings to loss of some genes or gain of others irrespective of their selective advantages or disadvantages.
(iii) Mutation The sudden heritable change which is directionless in gene is called mutation. It alters the genetic frequency or genetic make up of an individual.
(iv) Genetic Recombination This phenomenon occurs during gamete formation when chromosomes pass from parents to offsprings which show new combination of characteristics.
(v) Natural Selection It is a phenomenon by which some members of population having traits that enable them to grow and reproduce at higher rater are favoured. Hence, they leave more surviving offspring in the next generation than others.

Question. Explain divergent evolution in detail. What is the driving force behind it?
Answer : Divergent evolution is the evolution of a number of different forms of animals or plants froms of a common ancestral form. The driving force behind, it is adaptations to newly involved habitat and the prevailing environmental conditions there. As the original population increases in size, it spreads out from its centre of origin to exploit new habitas and food resources. In time this results in a number of populations each adapted to its particular habitat, eventually these populations will differ from each other sufficiently to become new species. A good example of this process is the evolution of the Australian marsupials into species adapted as carnivores, herbivores, burrowers, fliers, etc. Another example is that of peritadactyl limb in mammals. The flipper of a seal, wing of a bat, forelimb of a male, front legs of horse and the arm of a man perform different functions, but exhibit the same structural plan including same pentadactyl pattern of bones.

Question. You have studied the story of peppered moths in England. Had the industries been removed, what impact could it have on the moth population? Discuss. 
Answer : In the population of pepper moth two variants exist the dark and the light coloured. Before industrialisation, the light coloured moths were prevalent because they blended well with the lichen covered bark of the trees. The predators were unable to spot them and hence, their population were more in number. With industrialisation, the barks got covered with soot. The growth of lichens reduced, the light coloured moths were thus, spotted by the predators and their number decreased. However, the black variants were camouflased better on soot covered barks and their number increased drastically. If the industries were removed, the population of black moths would have declined because as stated before, they would not be able to camouflage against a light background (no black soot). Also the growth of lichens would increase. Therefore, the dark variants would be spotted better by predators and be eaten more frequently.

Question. What are the key concepts in the evolution theory of Darwin?
Answer : Key concepts of Darwin’s theory of evolution are as follows
(i) Over Production Living beings have an innate ability of producing own kind for the continuity of race. It has been observed that more individuals of each kind are produced than could possibly survive.
(ii) Struggle for Existence Individuals multiply in geometric ratio, whereas space and food remain almost limited.
(iii) Variations Members of a population vary is size, form and other characteristics even though they look superficially similar, no two individuals are alike. These variations are gradual and those with adaptive value are passed on to next generation.
(iv) Survival of the Fittest and Natural Selection During struggle for existence only those individuals could survive which exhibit beneficial variations and adapt better to changing environment. This is known as natural selection.
(v) Origin of Species Natural Selection results in modification of traits within a lineage, which over a period of long time can bring about evolution of original species into new one.

Question. Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Taking examples, describe the phenomenon.
Answer : This phenomenon indicated in the question is convergent evolution where by organisms, not closely related, evolve similar traits independently as a result of adaptation to similar environment. e.g.,
(i) Streamlined shape of sharks and dolphins. The former is a fish, while dolphin is a mammal, but both of them depend on swift movement through the water, so a streamlined shape is essential. Thus, it is the similar habitat that resulted in selection of similar adaptive features in different groups of organisms, but toward the same function.
(ii) Spines (modified leaves) and thorns (modified stems), both look similar and provide protection to the plant, but the plants to which they belong are distantly related.

Question. We are told that evolution is a continuing phenomenon for all living things. Are humans also evolving? Justify your answer.
Answer : New research suggests that despite modern technology and industrialisation, ‘humans continue to evolve’. In the last 10,000 years or so, the pace of our evolution has speeded up 100 times creating more mutations in our genes and hence, greater natural selection.
Some clues that show humans are evolving are
(i) Lactose Tolerance Historically the gene that regulated human’s ability to digest lactose was shut down as infants are weaned off of their mother’s breast milk. However, adult human in regions of Africa and Northern Europe developed the ability to tolerate lactose in their diets as recent as 5,000 or 6,000 years ago due to mutations.
(ii) Wisdom Teeth Our ancestors had much bigger jaws than we do to lactose their eating habits. Today our jaws are much smaller and wisdom teeth are often impacted estimates say that they will disappear in the coming population.

Question. Had Darwin been aware of Mendel’s work would he been able to explain the origin of variations. Discuss.
Answer : Yes, had Darwin been aware of Mendel’s work, he would have been able to explain the origin of variations. Darwins observation of different forms of an individual in a population could be related to the presence of different forms of alleles of a gene. The gene express as the most adaptive traits are selected naturally and become more abundant than those that are expressed as less adaptive traits. Over the time, the accumulation of these traits might change the species to an extent that it develops into a new one and adapted to the specific environment.

Important Questions for NCERT Class 12 Biology Evolution

Question. Mutations are :
(a) Random
(b) Directionless
(c) Both 1 and 2
(d) Always small
Answer : C

Question. Stanley Miller performed his experiment for explanation of origin of life, in which year ?
(a) 1953
(b) 1970
(c) 1870
(d) 1960
 Answer : A

Question. In some animals, the same structures developed along different directions due to adaptions to different needs this is called as :
(a) Divergent evolution
(b) Convergent evolution
(c) Parallel evolution
(d) None of these
 Answer : A

Question. Conventional religious literature tells us about the theory of special creation. Which of the following is/are included in the theory ?
(a) All living organisms that we see today were created as such
(b) The diversity was always the same since creation  and will be the same in future.
(c) Earth is about 4000 year old.
(d) All of these
 Answer : D

Question. Cranial capacity of homo erectus was about :
(a) 650-800 cc
(b) 1400 cc
(c) 900 cc
(d) 1600 cc
Answer : C

Question. Out of the following the theory of natural selection is based on certain observations, which are :
(A) Natural resources are limited
(B) Populations are stable in size except for seasonal fluctuations.
(C) Members of a population vary in characteristics even though they look superficially similar
(D) Most of variations are inherited
(a) A, C and D
(b) A, B, C and D
(c) B and C
(d) A, B and C
Answer : B

Question. The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas is called as :
(a) Convergent evolution
(b) Adaptive radiation
(c) Parallel evolution
(d) Continental drift
 Answer : B

Question. Why, pouched mammals survived in Australia?
(a) Divergent evolution
(b) Continental drift
(c) Adaptive radiation
(d) Convergent evolution.
Answer : B

Question. Dinosours disappeared around :
(a) 200 million years ago
(b) 20 million years ago
(c) 65 million years ago
(d) 65 billion years ago
 Answer : C

Question. The animals which evolved into the first amphibian that lived on both land and water, were :
(a) Jawless fish
(b) Lobefins
(c) Ichthyosours
(d) Shrew
 Answer : B

Question. Darwin worked on, which island for explanation of natural selection ?
(a) Malay archipelago
(b) Galapagos
(c) Sumatra
(d) Port Blaier
 Answer : B

Ques. From his experiments, S.L. Miller produced amino acids by mixing the following in a closed flask.
(a) CH₄, H₂, NH₃ and water vapor at 800°C
(b) CH₃, H₂, NH₄ and water vapor at 800°C
(c) CH₄, H2, NH₃ and water vapor at 600°C
(d) CH₃, H₂, NH₃ and water vapor at 600°C
Answer: A

Ques. Which of the following is the correct sequence of events in the origin of life?
I. Formation of protobionts
II. Synthesis of organic monomers
III. Synthesis of organic polymers
IV. Formation of DNA-based genetic systems
(a) I, II, III, IV (b) I, III, II, IV
(c) II, III, I, IV (d) II, III, IV, I
Answer: C

Ques. Following are the two statements regarding the origin of life.
(A) The earliest organisms that appeared on the earth were non-green and presumably anaerobes.
(B) The first autotrophic organisms were the chemoautotrophs that never released oxygen.
Of the above statements which one of the following options is correct?
(a) Both (A) and (B) are correct.
(b) Both (A) and (B) are false.
(c) (A) is correct but (B) is false.
(d) (B) is correct but (A) is false. 
Answer: A

Ques. Which one of the following is incorrect about the characteristics of protobionts (coacervates and microspheres) as envisaged in the abiogenic origin of life?
(a) They were partially isolated from the surroundings.
(b) They could maintain an internal environment.
(c) They were able to reproduce.
(d) They could separate combinations of molecules from the surroundings. 
Answer: C

Ques. The concept of chemical evolution is based on
(a) interaction of water, air and clay under intense heat
(b) effect of solar radiation on chemicals
(c) possible origin of life by combination of chemicals under suitable environmental conditions
(d) crystallisation of chemicals. 
Answer: C

Ques. Which of the following amino acids was not found to be synthesised in Miller’s experiment?
(a) Alanine
(b) Glycine
(c) Aspartic acid
(d) Glutamic acid
Answer: D

Ques. Which one of the following experiments suggests that simplest living organisms could not have originated spontaneously from non-living matter?
(a) Larvae could appear in decaying organic matter.
(b) Microbes did not appear in stored meat.
(c) Microbes appeared from unsterilised organic matter.
(d) Meat was not spoiled, when heated and kept sealed in a vessel. 
Answer: D

Ques. According to Oparin, which one of the following was not present in the primitive atmosphere of the earth?
(a) Methane
(b) Oxygen
(c) Hydrogen
(d) Water vapour
Answer: B

Ques. There is no life on moon due to the absence of
(a) O2
(b) water
(c) light
(d) temperature. 
Answer: B

Ques. Most abundant organic compound on earth is
(a) protein
(b) cellulose
(c) lipids
(d) steroids. 
Answer: B

Ques. 1st life on earth was
(a) cyanobacteria
(b) chemoheterotrophs
(c) autotrophs
(d) photoautotrophs.
Answer: B

Ques. The correct sequence for the manufacture of molecules/organic compounds on the primitive earth is
(a) NH3, nucleic acid, protein and carbohydrate
(b) protein, carbohydrate, water and nucleic acid
(c) NH3, protein, carbohydrate and nucleic acid
(d) NH3, water, nucleic acid and protein.
Answer: D

Ques. The first organisms were
(a) chemoautotrophs
(b) chemoheterotrophs
(c) autotrophs
(d) eukaryotes. 
Answer: B

Ques. Which was absent in the atmosphere at the time of origin of life?
(a) NH3
(b) H2
(c) O2
(d) CH4
Answer: C

Ques. Which one of the following sequences was proposed by Darwin and Wallace for organic evolution ?
(a) Overproduction, variations, constancy of population size, natural selection
(b) Variations, constancy of population size, overproduction, natural selection
(c) Overproduction, constancy of population size, variations, natural selection
(d) Variations, natural selection, overproduction, constancy of population size 
Answer: C

Ques. Darwin’s theory of pangenesis shows similarity with theory of inheritance of acquired characters then what shall be correct according to it?
(a) Useful organs becomes strong and developed while useless organs become extinct.
(b) Size of organs increase with aging.
(c) Development of organs is due to will power.
(d) There should be some physical basis of inheritance. 
Answer: D

Ques. Which of the following refer to correct example(s) of organisms which have evolved due to changes in environment brought about by anthropogenic action?
(1) Darwin’s Finches of Galapagos islands.
(2) Herbicide resistant weeds.
(3) Drug resistant eukaryotes.
(4) Man-created breeds of domesticated animals like dogs.
(a) only (1) (b) (1) and (3)
(c) (2), (3) and (4) (d) only (4) 
Answer: C

Ques. Embryological support for evolution was disapproved by
(a) Karl Ernst von Baer
(b) Alfred Wallace
(c) Charles Darwin
(d) Oparin. 
Answer: A

Ques. Flippers of penguins and dolphins are examples of
(a) adaptive radiation
(b) convergent evolution
(c) industrial melanism
(d) natural selection.
Answer: B

Ques. The similarity of bone structure in the forelimbs of many vertebrates is an example of
(a) homology
(b) analogy
(c) convergent evolution
(d) adaptive radiation.
Answer: A

Ques. Among the following sets of examples for divergent evolution, select the incorrect option.
(a) Forelimbs of man, bat and cheetah
(b) Heart of bat, man and cheetah
(c) Brain of bat, man and cheetah
(d) Eye of octopus, bat and man 
Answer: D

Question. Viviparity is considered to be more evolved because
(a) the young ones are left on their own
(b) the young ones are protected by a thick shell
(c) the young ones are protected inside the mother’s body and are looked after they are born leading to more chances of survival
(d) the embryo takes a long time to develop
Answer : C

Question. Evolution of different species in a given area starting from a point and spreading to other geographical areas is known as
(a) adaptive radiation
(b) natural selection
(c) migration
(d) divergent evolution.
Answer : A

Question. When two species of different genealogy come to resemble each other as a result of adaptation, the phenomenon is termed as
(a) microevolution
(b) co-evolution
(c) convergent evolution
(d) divergent evolution.
Answer : C

Question. For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively
The expected frequency of MN-blood group bearing organisms is likely to be
(a) 42%
(b) 49%
(c) 9%
(d) 58%
Answer : A

Question. Which of the following is an example for link species? 
(a) Lobe fish
(b) Dodo bird
(c) Sea weed
(d) Chimpanzee
Answer : D

Question. The concept of chemical evolution is based on
(a) interaction of water, air and clay under intense heat
(b) effect of solar radiation on chemicals
(c) possible origin of life by combination of chemicals under suitable environmental condition.
(d) crystallization of chemicals.
Answer : C

Question. The phenomenon of “Industrial melanism” demonstrates
(a) natural selection
(b) induced mutation
(c) genetic drift
(d) geographical isolation
Answer : A

Question. In 1953, S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for origin of first form of life from pre-existing non-living organic molecules. The primitive earth conditions created include 
(a) low temperature, volcanic storms, atmosphere rich in oxygen
(b) low temperature, volcanic storms, reducing atmosphere
(c) high temperature, volcanic storms, non-reducing atmosphere
(d) high temperature, volcanic storms, reducing atmosphere containing CH₄, NH₃, etc.
Answer : D

Question. Which is correct formula of Hardy-Weinberg’s law?
(a) p² + pq + q² = 0
(b) p² + pq + q2 = 1
(c) p² + pq + q² = infinity
(d) p² + 2pq + q² = 1
Answer : D

Question. Which type of selection explains industrial melanism observed in moth, Biston bitularia?
(a) Stabilising
(b) Directional
(c) Disruptive
(d) Artificial
Answer : B

Question. Fossils are generally found in 
(a) sedimentary rocks
(b) igneous rocks
(c) metamorphic rocks
(d) any type of rock
Answer : A

Question. According to Hugo de Vries, speciation is due to
(a) accumulation of small variations
(b) intraspecific breeding
(c) inter specific breeding
(d) saltation
Answer : D

Question. Match the scientists listed under column ‘I’ with ideas listed column ‘II’.
Column I                     Column II
A. Darwin              (i) Abiogenesis
B. Oparin              (ii) Use and disuse of organs
C. Lamarck           (iii) Continental drift theory
D. Wagner            (iv) Evolution by natural selection
(a) A-(i); B-(iv); C-(ii); D-(iii)
(b) A-(iv); B-(i); C-(ii); D-(iii)
(c) A-(ii); B-(iv); C-(iii); D-(i)
(d) A-(iv); B-(iii); C-(ii); D-(i)
Answer : B

Very Short Answer Questions

Question. According to deVries what is saltation?
Answer. According to de Vries, saltation is single step (large) mutation.

Question. Name the common ancestor of the great apes and man.
Answer. Dryopithecus/Ramapithecus

Question. State the significance of biochemical similarities amongst diverse organism in evolution.
Answer. Biochemical similarities indicate evolution from common or shared ancestry.

Question.  State the significance of Coelacanth in evolution. 
Answer. It is an ancestor of amphibians.

Question. Write the probable differences in eating habits of Homo habilis and Homo erectus.
Answer. Homo habilis did not eat meat. They were vegetarian.
Homo erectus ate meat. They were meat eater.

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

Short Answer Questions

Question. With the help of any two suitable examples explain the effect of anthropogenic actions on organic evolution. 
Answer.Charles Darwin, based on his observations during a sea voyage around the world in the ship H.M.S. Beagle, concluded the following:
- Varying degrees of similarities can be observed between existing life forms and those that existed millions of years ago.
-There has been gradual evolution of life forms with new forms arising at different periods of history.
- Any population has built-in variations in characteristics which adapt it better to environment.
- The characteristics which enable some populations or individuals to survive better in natural conditions (climate, food, physical factors) would out-breed others (Survival of the fittest).
- Those populations which are better fit (reproductively fit) in an environment will be selected by nature and will survive more (Natural selection).
- Adaptability is inherited and fitness is the end result of ability to adapt and get selected by nature.
Examples of natural selection.
(a) Industrial melanism:
- In England, before industrialisation in 1850’s, white-winged moths were more in number than dark-winged moths.
- But after industrialisation in 1920’s, dark-winged moths became more in number than whitewinged moths.
- This is because during industrialisation, the tree trunks covered by white lichens became dark due to deposition of dust and coal particles (soot and smoke).
- As a result, white-winged moths could be easily picked up by predators from the dark background and dark-winged moths survived.
- In mixed population, those that can better adapt, survived and there was increase in their population size.
(b) Chemical resistance:
- Excessive use of herbicides and pesticides has resulted in evolution of resistant varieties of microbes in much lesser time scale.
- Microbes are also becoming resistant to antibiotics and drugs because of same reason.
- As a result, pathogenic bacteria are appearing in very short period.
(c) Man has bred selected plants and animals and thus created new breeds with in short period of times.

Question. According to the Darwinian theory, the rate of appearance of new forms is linked to their life cycles. Explain. 
Answer. Microbes have a very short life cycle and divide fast. They can produce millions of organisms within few hours. Thus, it is easy to see variant population in less span of time. On the other hand, higher organisms have a long time span and the variations are not visible in a short time.

Question. What does the following equation represent? Explain.
p² +2pq+q² = 1
Answer.The equation represents Hardy-Weinberg’s Principle which states that allele frequencies in a population are stable and are constant from generation to generation. 1 represents stable allelic frequency indicating no evolution occurring. p represents frequency of homozygous dominant (AA), 2 pq represents frequency of heterozygous (Aa) and q represents frequency of homozygous recessive (aa).

Question. Gene flow occurs through generations and can occur across language barriers in humans. If we have a technique of measuring specific allele frequencies in different population of the world, can we not predict human migratory patterns in pre-history and history? Do you agree or disagree? Provide explanation to your answer. 
Answer. Yes, I agree. Gene flow occurs through generations. By studying specific allele frequencies, we can predict the human migratory patterns in pre-history and history. Studies have used specific genes/chromosomes/mitochondrial DNA to trace the evolutionary history and migratory patterns of humans (The project is known as the Human Genographics Project).

Question. What are we referring to when we say ‘simple organisms’ or ‘complex organisms’?
Answer. These are the terms to classify organisms according to their evolutionary history. Simple organisms have simple structural and functional organisation and are considered primitive,whereas complex organisms have complex structural and functional organisation and are said to have arise from simple organisms.

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

Question. Fill in the blank (i), (ii), (iii), (iv) with name of the mammals of Australia. 
Placental mammal           Marsupial mammal
Anteater                                     (i)
(ii)                                    Spotted cuscus
Bob cat                                     (iii)
(iv)                                  Tasmanian wolf
Answer. (i) Numbat (ii) Lemur
(iii) Tasmanian tiger cat (iv) Wolf

 QUESTIONS

1. Name one fish like reptile that evolved from land reptile about 200 million years ago?
2. For a long time, it was believed that life originated from decaying matter. What is this theory known as? Name the scientist who experimentally disproved this theory.
3. If abiotic origin of life is in progress on a planet other than earth, what should be the conditions there?
4. Name the person who proposed that population tends to increase geometrically while food production increases arithmetically.
5. Name the scientist who had also come to similar conclusion as that of Darwin about natural selection as a mechanism of evolution. Which place did he visit to come to conclusions?
6. Explain Oparin-Haldane theory of chemical evolution of life.
7. Distinguish between convergent and divergent evolution giving one example of each.
8. What is adaptive radiation? Explain with an example.
9. How did Louis Pasteur disprove spontaneous generation theory?