Class 12 Biology Chapter 7 Important Questions Evolution

Question 14.
Explain with the help of an example the type of evolution homology is based on. (Delhi 2015C)
Or
Divergent evolution leads to homologous structures. Explain with the help of an example. (All India 2011C)
Answer:
Divergent evolution is a process, where the same structure develops along different directions in different organisms due to adaptations to different needs. Divergent evolution leads to the development of homologous structures, as they all have similar anatomical structure and origin, but perform different functions.

Examples, the thorn of Bougainvillea and tendrils of Cucurbita are homologous organs as both of them are modified axillary buds, which perform different functions.

Question 15.
(i) Explain adaptive radiation with the help of 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 is it so named? (All India 2014)
Answer:
(i) The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas or habitat is called adaptive radiation, e.g. alterations in beaks of finches on Galapagos Islands.

(ii) An example where more than one adaptive radiation have occur in an isolated geographical area is Australian marsupials, where a number of different marsupials evolved from an ancestral stock but within the isolated Australian island and all of them got adapted to different habitats, e.g. Tasmanian wolf (marsupial) and placental wolf (placental
mammals).

The above cited example depicts convergent evolution as these marsupials show development of similar adaptive functional structures in unrelated groups of organisms.

Question 16.
What was proposed by Oparin and Haldane on origin of life? How did SL Miller’s experiment support their proposal? (Foreign 2014)
Or
Mention the contribution of SL Miller’s experiment to origin of life. (Delhi 2010)
Answer:
Oparin and Haldane proposed that life originated on earth spontaneously from non-living matter, i.e. organic molecules.

SL Miller conducted an experiment, which provided experimental evidence for chemical evolution. He created conditions similar to primitive atmosphere, in the laboratory such as high temperature, reducing atmosphere consisting of CH₄, NH₃, etc. When he created an electric discharge in the flask containing all the above stated components at 800°C, organic molecules, e.g. amino acids were formed. Results indicated that the first non-cellular forms of life were created about 3 billion years ago. This also supports the hypothesis that life could have originated from organic matter.

Question 17.
List the two main propositions of Oparin and Haldane. (All India 2013)
Answer:
Two main propositions of Oparin and Haldane were

• The primitive atmosphere was reducing, i.e. free oxygen was absent.
• There was high temperature, high methane, ammonia and hydrogen gas in the atmosphere.

Question 18.
How do palaeontological evidences support evolution of organisms on earth? (All India 2013C)
Answer:
Palaeontology is the study of past life based on fossil records. The study of fossils reveals the type of life forms occurring in the past and highlights the course of evolution of living organisms. The distribution of fossils in the sedimentary rocks of different ages fully supports the concept of evolution. It shows that structure of wing became more and more complex as we proceed from earliest to recent times. From the fossil records it has been concluded that evolution has taken place from the simple to complex forms in a gradual manner.

Question 19.
Write the Oparin and Haldane’s hypothesis about the origin of life on earth. How does meteorite analysis favour this hypothesis? (All India 2013)
Answer:
Oparin-Haldane theory states that origin of life is the result of a long series of physiochemical changes, brought about first by chemical evolution and then by biological evolution.

Analysis of meteorites also revealed the presence of similar compounds as found in the primitive atmosphere, indicating the occurrence of similar processes elsewhere in space.

Question 20.
Convergent evolution leads to analogous structures. Explain with the help of an example. (All India 2011C)
Answer:
Convergent evolution is a process of evolution, where anatomically dissimilar structures in different organisms perform similar functions. It leads to the formation of analogous structures in different groups of organisms as they perform similar function, but are anatomically different.

Examples, potato (stem modification) and sweet potato (root modification), flippers of penguins and dolphins.

Question 21.
Why are wings of butterfly and birds said to be analogous organs? Name the type of evolution the analogous organs are a result of. (Foreign 2010)
Answer:
Refer to Answer No. 11.

Question 22.
(i) Differentiate between analogous and homologous structures.
(ii) Select and write analogous structures from the list given below.
(a) Wings of butterfly and birds
(b) Vertebrate hearts
(c) Tendrils of Bougainvillea and Cucurbita
(d) Tubers of sweet potato and potato. (2018)
Answer:
(i) Differences between analogous structure and homologous structure are as follows

(ii) Analogous organs
(a) Wings of butterfly and birds.
(b) Tubers of sweet potato and potato.

Question 23.
How do homologous organs represent divergent evolution? Explain with the help of a suitable example. (Delhi 2016)
Answer:
Homologous organs as divergent evolution: Homology is the relation among the organs of different groups of organisms, that show similarity in the basic structure and embryonic development, but have different functions. Homology in organs indicates common ancestry. It is based on divergent evolution. When due to different needs, some structures develop differently, the condition is called divergent evolution. This results in the formation of homologous organs. Examples of homology in plants and animals are as follows

Question 24.
Differentiate between homology and analogy. Give one example of each. (All India 2016)
Or
Differentiate between divergent and convergent evolution. Give one example of each. (Outside Delhi 2016)
Answer:
Differences between homology and analogy are as follows

Question 25.
Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life. (Delhi 2016C)
Answer:
Theory of spontaneous generation states that the life originate;! from dead, decaying or rolling matters like storm, dead animals, etc.
Louis Pasteur rejected the theory of spontaneous generation and demonstrated that life had evoived from pre-existing life. In his experiment, he kept killed yeast cells in presterilised flask and in another flask open into air. The life did not evolved in the former, but new living organisms evolved in the another flask.

Question 26.
Explain convergent evolution with the help of two examples. (Foreign 2015)
Answer:
Refer to Answer No. 20.

Question 27.
Explain adaptive radiation with the help of a suitable example. (Delhi 2015)
Or
What do you infer from the resemblance between flying squirrel and flying phalanger with reference to their evolution. Delhi 2015,2015C Or Explain adaptive radiation and
convergent evolution by taking example of some of Australian marsupials and Australian placental mammals. Foreign 2010 Or Australian marsupials and placental mammals are suitable examples of adaptive radiation and convergent evolution. Explain by giving reasons. All Indio 2010C
Answer:
Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and radiating to other habitats.
Darwin went to Galapagos Island and observed that there were many varieties of finches in the same island. All the varieties evolved on the island itself. Darwin suggested that after originating from a common ancestral seed eating stock, the finches must have radiated to different geographical areas and undergone adaptive changes in their beaks, thus enabling some to become insectivorous while the other remained herbivore and ate seeds.
Or
Many Australian marsupials, each different from the other, e.g. kangaroo, sugar glider, etc., evolved from a common ancestral stock, but all within the Australian Island continent. When more than one adaptive radiation occur in an isolated geographical area, it can be called as convergent evolution. Australian placental mammals also show adaptive radiation in evolving into varieties of such placental mammals, each one of which appears similar to a corresponding marsupial, e.g. placental wolf and Tasmanian wolf, anteater and numbat, flying squirrel and flying phalanger, etc.

Question 28.
Explain the interpretation of Charles Darwin who observed a variety of small black birds on Galapagos Islands. (Delhi 2015)
Answer:
(i) Darwin found the variations in the beaks of small black birds on Galapagos Island due to their adaptation to different food habits.

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

Question 29.
How does the study of fossils support evolution? Explain. (Delhi 2015C)
Answer:
Refer to Answer No. 18.

Question 30.
Given below is a diagrammatic representation of the experimental setup used by SL Miller for his experiment.

(i) Write the names of different gases contained and the conditions set for the reaction in the flask A.
(ii) State the type of organic molecule he collected in the water at B.
(iii) Write the conclusion he arrived at. (Delhi 2013C, Foreign 2011)
Answer:
(i) Gases were methane, ammonia, hydrogen and water vapour. In ‘A’ flask electric discharge was created using electrodes.
(ii) The organic molecules collected in water at ‘B’ were amino acids.
(iii) He concluded that life could have come from pre-existing non-living organic molecules and their formation was preceded by chemical evolution.

Question 31.
State the theory of biogenesis. How does Miller’s experiment support this theory? (Delhi 2012)
Or
State the views of Oparin and Haldane on evolution. How does SL Miller’s experiment support their views? (Delhi 2011C)
Answer:
The theory of biogenesis was proposed by Oparin and Haldane. It states that life could have come from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and the formation of life forms was preceded by chemical evolution, i.e. formation of diverse organic molecules from inorganic constituents.

In 1953, Urey and Miller conducted an experiment to prove this theory. They created the conditions of primitive earth, i.e. high temperature, volcanic storms, reducing atmosphere containingCH₄, NH₃, etc., at laboratory scale. They then stimulated electric discharge in a closed flask containing CH₄,H₂, NH₃ and water vapour at 800°C. They observed the formation of amino acids.

In similar experiments, they observed the formation of sugars, nitrogen bases, pigments and fats. These small organic molecules are the building blocks for proteins and other components. Hence, this experiment supported that life has came from pre-existing non-living organic molecules.

Question 32.
Convergent evolution and divergent evolution are the two concepts explaining organic evolution. Explain each one with the help of an example. (Foreign 2011; Delhi 2010)
Answer:
Refer to Answer No. 14 and 20.

Question 33.
Anthropogenic actions hasten evolution. Explain with the help of suitable example. (Foreign 2010)
Answer:
Human activities, i.e. anthropogenic actions are found to enhance evolution.
For example,
(i) Excessive use of DDT as a fertiliser in crops resulted in the evolution of DDT resistant mosquitoes.

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

(ii) Similarly, evolution of antibiotic resistant microbes has occurred due to the overuse of antibiotics.

Question 34.
(i) Differentiate between analogy and homology giving one example each of plant and. animal, respectively.
(ii) How are they considered as an evidence in support of evolution? (All India 2016)
Answer:
(i) Refer to Answer No. 24.
(ii) Homology and analogy show the similarities and differences among the organisms of today and those existed years ago. These evidences come from the comparative study of external and internal structure.

These can be determined by the following types Homology in organs indicates common ancestry. It is based on divergent evolution. When due to different needs, some morphologically similar structures develop differently, to perform different functions, the condition is called divergent evolution. This results in the formation of homologous organs.
Analogy had developed due to the convergent evolution where different structures evolved for the same function and have morphologically dissimilar structures. These are called analogous organs.

Question 35.
(i) List any four evidences of evolution, (ii) Explain, any one of the evidences that helps to understand, the concept of evolution. (Delhi 2016C)
Answer:
(i) Evidences of evolution are derived from

• Palaeontology (Fossils)
• Comparative anatomy and morphology, i.e. homology and analogy
• Biochemical/Physiology
• Biogeography
• Embryology

(ii) Comparative anatomy and morphological evidences show the similarities and differences among the organisms of today and those that existed years ago.

The evidences come from comparative study of external and internal structure.
I. (a) The organs with same structural design and origin, but different functions are called homologous organs.
Examples are forelimbs of some animals like whales, bats and cheetah have similar anatomical structure, such as humerus, radius, ulna, carpals, metacarpals and phalanges.
(b) Homology in organ indicates common ancestry.
(c) Other examples of homology are vertebrate heart or brain. In plants also, thorns and tendrils of Bougainvillea and Cucurbita represent homology.
(d) Homology is based on divergent evolution. The same structures developed along different directions due to adaptations to different needs. The condition is called divergent evolution.

II. (a) Organs which are anatomically different, but functionally similar are called analogous organs.
For example, wings of butterfly and birds. In both, wings perform same function, but they have different origin and structure.
(b) Analogy refers to a situation exactly opposite to homology.
(c) Analogous organs are a result of convergent evolution. It is the evolution in which different structures evolve for same function and hence, have similarity. It can be said that above organisms had different structures, but they came in the same environment and evolved to perform same function.
(d) Other examples of analogy are eyes of Octopus and mammals; flippers of penguins and dolphins.

In plants, syveet potato (root modification) and potato (stem modification) are analogous organs.

Question 36.
(i) How does the study of fossils help to understand evolution?
(ii) How did SL Miller provide an experimental evidence in favour of Oparin and Haldane’s hypothesis? Explain. (Delhi 2016C)
Answer:
(i) The fossils are the remains of past organisms preserved in sedimentary rocks.
Palaeontology is the study of fossils.

• Rocks form sediments and a cross-section of earth’s crust indicate the arrangement of sediments one over the other during the long history of earth.
• Different aged rock sediments contain fossils of different life forms, who died during the formation of the particular sediment.
  Fossils which were present in a specific area explain the presence of that organism in that area only.
• Some organisms appear similar to modern organisms. They represent extinct organisms like dinosaurs.
• A study of fossils in different sedimentary layers indicates the geological period in which they existed.
  Fossils which are obtained from old rocks are of simple type, while which were obtained from new rocks are of complex type.
• The study showed that life forms varied over time and certain life forms are restricted to certain geological time scale. Hence, new forms of life have evolved at different times in the history of earth. Thus, palaeontological evidences help in detailed study of progress of evolution from old to new forms.

(ii) Refer to Answer No. 31.

Question 37.
According to the Hardy-Weinberg principle, the allele frequency of a population remains constant. How do you interpret the change of frequency of alleles in a population? (All India 2019)
Answer:
According to Hardy-Weinberg principle, the change in frequency of alleles in a population shows the extent of evolutionary change.

Question 38.
Coelacanth was caught in South Africa. State the significance of discovery of Coelacanth in the evolutionary history of vertebrates. (All India 2019)
Or
State the significance of Coelacanth in evolution. (Delhi 2012)
Or
Coelacanth was caught in 1938 in South Africa. Why is it very significant in the evolutionary history of vertebrates? (All India 2010C)
Answer:
The discovery of Coelacanth (lobefins), the first amphibian is significant as it proved that amphibians have evolved from fish-like organisms. Lobefins were the ancestors of modern day frogs and salamanders.

Question 39.
How did Charles Darwin express fitness ? (Delhi 2019)
Or
What is ‘fitness of an individual’ according to Darwin? (Delhi 2017)
Answer:
According to Darwin, fitness of an individual is the ability of an organism to reproduce successfully and leave a large number of progenies under a particular set of selection pressures.

Question 40.
Write the names of the following:
(i) A 15 mya primate that was ape-like
(ii) A 2 mya primate that lived in East African grasslands. (2018)
Answer:
(i) Dryopithecus (ii) Australopithecus

Question 41.
What role does an individual organism play as per Darwin’s theory of natural selection? (Delhi 2017)
Answer:
According to the Darwin’s theory of natural selection, the role of an individual organism is to pass on the necessary variations, changes or mutations from present generation to the next generation, that has been selected by the nature.

Question 42.
Write the probable differences in eating habits of Homo habilis and Homo erectus. (Foreign 2016)
Answer:
The probable differences in eating habit of Homo habilis and Homo erectus are as follows
Homo habilis They did not eat meat.
Homo erectus They probably ate meat.

Question 43.
According to Hugo de Vries what is saltation? (All India 2016)
Or
What is ‘Saltation’ according to Hugo de Vries? (Delhi 2014)
Answer:
Mutation theory of Hugo de Vries states that the evolution occurs due to single-step large mutations occurring in a population. This is called saltation and it leads to new species formation or speciation.

Question 44.
State a reason for the increased population of dark coloured moths coinciding with the loss of lichens (on tree bark) during industrialisation period in England. (Delhi 2015)
Answer:
The increase in dark population of moths was due to industrial melanism.
After industrialisation, dark-winged moths became more than white-winged moths. This is because tree trunks covered by lichens became dark due to the air pollution during industrialisation. White-winged moths fail to camouflage and thus, decreased in number, whereas dark-winged moths were able to escape predation.

Question 45.
Write the basis of origin of variations in organisms as described by Hugo de Vries. (All India 2013C)
Answer:
Mutations are the basis of origin of variations in an organism according to Hugo de Vries.

Question 46.
Name the common ancestor of the great apes and man. (All India 2011)
Answer:
Dryopithecus is the common ancestor of great apes and man.

Question 47.
Mention how is mutation theory of Hugo de Vries different from Darwin’s theory of natural selection. (Foreign 2011)
Answer:
Hugo de Vries theory It states that evolution occurs due to single step large mutations called saltation, whereas Darwin’s theory states that the speciation occurs gradually through a number of generations, with the accumulation of minor variations.

Question 48.
List the two characteristics of mutation that help in explaining evolution. (Delhi 2011c)
Answer:
According to mutation theory of evolution

1. Mutation are random, inheritable and appear in all conceivable directions.
2. Same type of mutations can appear in number of individuals of a species.

Question 49.
When does a species become founder to cause founder effect? (Foreign 2010).
Answer:
Founders effect occurs due to the change in allele frequency of a population. When the change in the allele frequency is very different in the new sample of population, so that they become a different species. The original drifted population becomes founder and the effect is called founder effect.

Question 50.

Study the ladder of human evolution given above and answer the following questions.
(i) Where did Australopithecus evolve?
(ii) Write the scientific name of Java man. (Delhi 2010C)
Answer:
(i) Australopithecus evolved in East African grasslands.
(ii) Java man -Homo erectus.

Question 51.
How would the gene flow or genetic drift affect the population in which either of them happen to take place ? (Delhi 2019)
Answer:
If gene flow or genetic drift takes place in a population, the effect would be

• Gene flow/Gene migration Due to migration, new genes or alleles are added to the population and are lost from the old population thus, changing the frequencies of alleles in both populations. When migration occurs multiple times it is termed as gene flow.
• Genetic drift Changes occurring in allele frequencies by chance is called genetic drift. Due to changes in allele frequency in new population, some different species are formed. This is called founder effect and the original population is called founder.

Question 52.
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 ? (2018)
Answer:
Hardy-Weinberg’s principle states that allele frequencies in a population are stable. They remain constant from generation to generation. The gene pool also remains constant. This is called genetic equilibrium.

Thus, according to this principle, the sum total of all the allelic frequencies in a population is always 1. Suppose in a diploid individual, p and q represent the frequency of allele A and allele a, respectively. The probability that an allele A with a frequency of P appears on both the chromosomes of a diploid organism in the p². Similarly of aa is q², of Aa is 2pq. Hence, p² + 2pq + q² = 1.

The difference measured in the expected values of frequencies, indicates the extent of evolutionary change.

Question 53.
Mention the evolutionary significance of the following organisms:
(i) Shrews
(ii) Lobefins
(iii) Homo habilis
(iv) Homo erectus (Delhi 2017)
Answer:
The evolutionary significance of the given organisms are as follows
(i) Shrews They are the first mammals. These were long tailed, insectivorous, squirrel-like organisms. They gave rise to primitive primates. For example, leones and tarsiers at the beginning of the Palaeocene era.
(ii) Lobefisns They are the first amphibians. Modem day frogs and salamanders have evolved from them.
(iii) Homo habilis The first human-like primates who lived in Africa about 2 million years ago. They had brain capacity of 700 cc. They are also called as handy man as they were first and the most skillful tool makers.
(iv) Homo erectus They appeared after Homo habilis, about 1.7 million years ago. They had large brain capacities, i.e. 800-1100 cc and were omnivores.

Question 54.
Name the first human-like hominid. Mention his food habit and brain capacity. (All India 2015C)
Answer:
Homo habilis were the first human-like hominid. They probably did not consume meat and their brain capacity was about 650-850cc.

Question 55.
Explain how natural selection operates in nature by taking an example of white-winged and dark-winged moths of England. (All India 2014C)
Answer:
In England, prior to industrialisation, the tree trunks were covered with white lichens hence, white moths tould survive and were protected from predators due to white colour. On the other hand, black moths (a dark-winged moths) could be easily identified due to their dark colour and declined in number due to predation.

However, as industrialisation progressed, the lichens were replaced by soot and dust particles and dark coloured moths were benefitted due to camouflage, while white-winged moths could be easily eaten up by the predators being easily identifiable. Thus, only the dark-winged moths who were able to fit and survive, i.e. adapted well in conditions, reproduced well in nature. Thus, natural selection operates in nature by selecting the fittest characters of organisms.

Question 56.
Rearrange the following in increasing order of evolution
Gnetales; Ferns; Zosterophyllum; Ginkgo. (2014C)
Answer:
The increasing order of evolution in plants is as follows: Zcsterophyllum – Ferns – Ginkgo – Gnetales

Question 57.
Name the ancestors of a man based on the features given below.
(i) Human-like, meat-eater with 900 cc brain, lived in Java.
(ii) More human-like with brain size 1400 cc, lived in Central Asia, used hides and buried their dead.
(iii) Human-like, vegetarian, with brain capacity between 650-800 cc.
(iv) Man-like primate, that existed about 15 my a. Fossils found in Tanzania. (All India 2013C)
Answer:
(i) Homo erectus
(ii) Homo sapienes neanderthalensis
(iii) Homo habilis
(iv) Ramapithecus

Question 58.
Explain the phenomenon of evolution by natural selection as supported by the variations observed in white-winged and dark-winged moth populations in England between 1850-1920. (All India 2019)
Answer:
Refer to Answer No. 19.

Question 59.
(i) Write two differences between Homo erectus and Homo habilis.
(ii) Rearrange the following from early to late geological periods:
Carboniferous, Silurian, Jurassic. (Delhi 2019)
Answer:
(i) Differences between Homo erectus and Homo habilis are

(ii) The correct sequence from early to late geological period is Silurian → Carboniferous → rassic.

Question 60.
How can Hardy-Weinberg equilibrium be affected? Explain giving three reasons. (2018C)
Or
Giving three reasons, write how Hardy-Weinberg equilibrium can be affected. (Delhi 2014C)
Answer:
Factors which affect Hardy-Weinberg equilibrium are (Any three)

• Gene migration Due to migration, new genes or alleles are added to the population and are lost from the old population thus, changing the frequencies of population. Migration when happens multiple times, is termed as gene flow.
• Genetic drift Changes occurring in frequencies by chance are called genetic drift. Due to changes in allele frequency in new population, some different species are formed. This is called founder effect and the original population is called founder.
• Mutations These occur randomly and at a very slow rate. They lead to new phenotypes and due to considerable genetic variations, speciation occurs.
• Recombination During gainetogenesis, crossing over between homologous chromosomes leads to new combinations of genes. It occurs during meiosis.

Question 61.
Write the characteristics of Ramapithecus, Dryopithecus and Neanderthal man. (All India 2017)
Answer:
Characteristics of Ramapithecus

• Ramapithecus survived about 14-15 million years ago during late Miocene to Pliocene.
• Ramapithecus walked erect on its hindlegs.
• They were similar to ape, which lived on the tree tops, but also walked on the ground.
• They ate hard nuts and seeds like modem man. Their jaws and teeth were similar to humans.

Characteristics of Dryopithecus

• They lived about 25 million years ago during Miocene period.
• Legs and heels indicate that Dryopithecus was of a semi-erect posture and Knuckle walker.
• Dryopithecus was arboreal and herbivorous, who ate soft fruits and leaves.
• Dryopithecus had large canines and incisors.

Characteristics of Neanderthal man

• Neanderthal man existed in the late Pleistocene period.
• Neanderthal walked upright with bipedal movement.
• The face was slightly prognathous and had low brows, receding jaws and high domed heads.
• The cranial capacity of Neanderthal man was about 1300-1600cc and of average 1450cc. Their jaws were deep with no chin and skull bones were thick.

Question 62.
p² + 2pq + q² = 1. Explain this algebraic equation on the basis of Hardy-Weinberg’s principle. (Delhi 2017)
Answer:
The equation p² + 2pq + q² = 1, mathematically represents the Hardy-Weinberg’s principle. It is used to calculate the genetic variations among a population at equilibrium.
Principle It states that allele frequencies in a population are stable and remain constant from generation to generation.
In this equation,
p – frequency of allele A
q – frequency of allele a
p² – frequency of AA (homozygous) individuals in a population
q² – frequency of aa (homozygous) individuals
2pq – frequency of Aa (heterozygous) individuals

Also, the sum total of all the allelic frequencies is equal to 1. If the p and q allele frequencies are known, then the frequencies of three genotypes can be calculated using the Hardy-Weinberg’s equation. This equation can be used to measure the differences in frequencies of observed genotype measured from the frequencies predicted by the equation. The disturbance in genetic equilibrium results in evolution, thus the presence of any difference indicates the extent of evolutionary change.

Question 63.
How did industrialisation play a role in natural selection of light and dark coloured moth in England? (Delhi 2015C)
Or
Explain the increase in the numbers of melanic (dark-winged) moths in the urban areas of post-industrialisation period in England. (Delhi 2012)
Answer:
Refer to Answer No. 19.

Question 64.
Since the origin of life on earth, there were five episodes of mass extinction of species.
(i) How is the sixth extinction presently in progress, different from the previous episodes?
(ii) Who is mainly responsible for the sixth extinction?
(iii) List any four points that can help to overcome this disaster. (All India 2014)
Answer:
(i) Sixth extinction is different from previous episodes in the following ways

• It takes place rapidly, due to the reduction in number of species per unit area per unit time.
• In contrast to previous episodes which were naturally driven, sixth extinction is accelerated by human activities such as deforestation, industrialisation, etc.

(ii) Human activities that ultimately lead to global warming and disruption of environmental and ecological balance are responsible for sixth extinction.

(iii) The four measures that can be implemented to overcome this disaster are

• Aforestation.
• Reduction in overexploitation of natural resources.
• Conservation of species and their natural habitats to minimise their losses.
• Create awareness among people regarding global warming and its consequences.

Question 65.
Describe the three different ways by which natural selection can affect the frequency of a heritable trait in a population. (Foreign 2014)
Or
Explain the three ways in which natural selection operates on different traits in nature. (All India 2010)
Answer:
The three different ways by which natural selection can affect the frequency of a heritable trait in a population are
(i) Stabilisation It results in more number of individuals acquiring the mean character value, i.e. variation is much reduced.
(ii) Directional change It results in more individuals acquiring value other than mean character value, i.e. the peak shifts towards one direction.
(iii) Disruption In this, more individuals acquire peripheral character value at both ends of the distribution curve, i.e. two peaks are formed at periphery.

Question 66.
According to Darwinian theory, the rate of appearance of new forms is linked to their life cycles. Explain. (All India 2014C)
Answer:
Darwin’s theory states that the fitness of an organism is measured by its reproductive ability. The appearance of new forms is linked to the lifespan of an organism.
The greater lifespan of an individual indicates that the more it can reproduce and hence, greater new forms would appear. This can be observed in the development of dark-winged moths due to industrial melanism.
Refer to Answer No. 19.

Question 67.
Study the schematic representation of evolutionary history of plant forms given below and mention:

(i) The plant forms ferns and conifers are most related to.
(ii) The nearest ancestors of flowering plants.
(iii) The most primitive group of plants.
(iv) Common ancestry of Psilophyton provides to.
(v) The common ancestor of Psilophyton and seed ferns.
(vi) The common ancestors of mosses and tracheophytes. (Delhi 2012C)
Answer:
(i) Psilophyton
(ii) Seed ferns,
(iii) Chlorophyte ancestor
(iv) Ferns, conifers and seeds ferns
(v) Tracheophyte ancestor
(vi) Chlorophyte ancestor.

Question 68.
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. (All India 2011)
Answer:
The two key concepts of Darwinian theory of natural selection are as follows Branching Descent

• Members of a population vary in characteristics, even though they look superficially similar. Most of these variations are heritable.
• Accumulation of variations over a period of time through a number of generations leads to change in population characteristics.

e.g. Evolution of marsupials of Australia derived from a common ancestor. Natural selection Nature selects those individuals who are fit in the environment. Fitness according to Darwin is reproductive fitness.

Those who adapt better to the habitat reproduce more and their progeny consists of more fit individuals, who are selected by nature, e.g. Industrial melanism.

Question 69.
(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. (All India 2010)
Answer:
(i) The expression states that the sum total of all the allele frequencies is one. Suppose there are two alleles ‘A’ and ‘a’ in a population. Their frequencies are p and q, respectively. The frequency of ‘AA’ individual in a population is p².
It can be explained that the probability that an allele ‘A’ with a frequency p appears on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e. p².
In the same way, the frequency for aa is q² and for Aa it is 2 pq.
p² + 2 pq + q² = 1
where, p² represents the frequency of homozygous dominant genotype,
2 pq represents the frequency of the heterozygous genotype and q² represents the frequency of homozygous recessive.

(ii) Genetic equilibrium is disturbed by the factors like gene migration, genetic drift, mutation and gene recombination during gamete formation. Refer to Answer No. 24. (1)

Question 70.
(i) How does Hardy-Weinberg equation explain genetic equilibrium?
(ii) Describe how this equilibrium gets disturbed which may lead to founder effect. (All India, 2019, Foreign 2012)
Or
(i) Describe Hardy-Weinberg principle
(ii) List any four factors, which affect genetic equilibrium.
(iii) Describe founder effect. (Foreign 2014)
Answer:
(i) According to Hardy-Weinberg principle, the allele frequencies in a population are stable and are constant from generation to generation.

(ii) The four factors that affect genetic equilibrium are

• Gene migration
• Genetic drift
• Mutation and recombination
• Natural selection

(iii) Whenever the gene migration occurs multiple times, it leads to some changes, that may sometimes result in change in allele frequency (at random or by chance).
This difference in allele frequency leads to a new sample of population in such a way that they evolve into a different species. Such populations are called founders and the effect generated is called founder effect.

Question 71.
(i) Explain Darwinian theory of evolution with the help of one suitable example. State the two key concepts of theory.
(ii) Mention any three characteristics of Neanderthal man that lived in near East and Central Asia. (Delhi 2014)
Answer:
(i) Darwinian theory of evolution/Darwin’s theory of Natural Selection:

• All the populations have built in variations for each character, which help them to adapt better to the environment.
• The characteristics, which enable some populations to survive better in natural conditions (climate, food, physical factors) would outbreed others (survival of the fittest).
• The population, which better fits in an environment is selected by nature and survives more (natural selection).
• Adaptability is inherited and fitness is the end result of ability to adapt and get selected by nature.

The two key concepts of Darwinian theory are:

• Branching descent and
• Natural selection
  (For details, Refer to Answer No. 32).

(ii) The three characteristics of Neanderthal man that lived in near East and Central Asia are:

• Walked upright with bipedal movement.
• Cranial capacity was around 1300-1600 cc.
• Face slightly prognathous and jaws were deep with no chin.

Question 72.
How does the process of natural selection affect Hardy-Weinberg equilibrium? Explain. List the other four factors that disturb the equilibrium. (All India 2013)
Answer:
Natural selection affects Hardy-Weinberg equilibrium in the following ways:

• It is a process in which heritable variations help in the survival of an organism, enabling it to reproduce and give rise to a large number of offsprings.
• There may be change in the frequency of genes and alleles in the future generations.
• It leads to the formation of new species. Hardy-Weinberg law states that allelic frequencies in a population are stable and remain constant from generation to generation but natural selection allows only one allele to adapt to changing conditions.

For other factors affecting Hardy-Weinberg equilibrium, Refer to Answer No. 24.

Question 73.
(i) Explain the process of natural selection that leads to speciation.
(ii) List the three ways in which the process operates in nature. Explain any one of processes. (Foreign 2012)
Answer:
(i) Natural Selection Refer to Answer No. 35.
(ii) Refer to Answer No. 29.

Question 74.
(i) Name the primates that lived about 15 million years ago. List their characteristic features.
(ii) (a) Where was the man-like animal found?
(b) Write the order in which Neanderthals, Homo habilis and Homo erectus appeared on the earth. State the brain capacity of each of them.
(c) When did modern man Homo sapiens appear on this planet? (Delhi 2011)
Answer:
(i) Dryopithecus and Ramapithecus are the primates that lived about 15 million years ago.
Their characteristics are

• They were hairy.
• They walked like gorillas and chimpanzees. Dryopithecus was more ape-like, while Ramapithecus was more man-like.

(ii) (a) The man-like animal was found in East African grasslands.
(b) They appeared in the following order Homo habilis → Homo erectus → Neanderthal. They had brain capacities of 650-800 cc, 900 cc and 1400 cc, respectively.
(c) During ice age between 75000-10000 years ago, modern man Homo sapiens appeared on this planet.

Question 75.
Explain the salient features of Hugo de Vries theory of mutation. How is Darwin’s theory of natural selection different from it? Explain. Delhi 2011
Answer:
Hugo de Vries explained that new species arise from pre-existing ones in a single generation by a sudden appearance of marked differences called mutations. He believed that it is mutation, which causes evolution.

The differences between de Vries theory and Darwin theory are as follows

Question 76.
(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. (Delhi 2010)

Answer:
(i) Refer to Answer No. 34 (i).
(ii) Refer to Answer No. 29.

Question 77.
(i) Natural selection operates when nature-selects for fitness. Explain,
(ii) The rate of appearance of new forms is linked to the lifespan of an organism. Explain with the help of a suitable example. (Delhi 2010)
Answer:
(i) The members of a population vary in characteristics even though they look similar. The population usually increases exponentially but the natural resources are limited leading to more competition. The individuals, which are fit and can adapt themselves are able to survive. They grow, reproduce and survive. This is called natural selection as stated by Darwin.

(ii) Refer to Answer No. 30.

Question 78.
(i) How do the observations made during moth collection in pre and post-industrialised era in England to support evolution by natural selection?
(ii) Explain the phenomenon that is well-represented by Darwin’s finches other than natural selection. (Delhi 2017)
Answer:
(i) Natural selection is the key concept of Darwin’s theory of evolution which was explained by Charles Robert Darwin. According to this theory, population of all organisms exhibits variations in characteristics, which help them to adapt better to environment. It means that individuals of a population are never same.

Some of these characteristics, enable individuals to survive better in natural conditions and reproduce. This is called as the survival of the fittest. The organisms which adapt well in the environment are selected by nature and thus, survive more in nature.

This is called natural selection. From the description given below, we can figure out that how the observations made during moth collection in pre and post-industrialised era in England supported the idea of evolution by natural selection.

Industrial melanism There are two varieties of moth, white-winged and dark-winged.
(a) Before industrial revolution in England, white-winged moths were more in number than dark-winged moths, because there was less pollution, which led to light trunk of trees due to the presence of lichen on them. So, on light background white-winged moths were not visible, while dark-winged moths could be eaten by predators very easily.

(b) After industrialisation, dark-winged moths became more than white-winged moths. This is because during industrialisation, tree trunks covered by white lichens became dark due to air pollution (dust and soot particles). So, now white-winged moths could be detected easily. Due to this, white-winged moths could be easily eaten up by the predators as they fail to camouflage. Whereas dark-winged moths escape predation. So, nature selected only those moths which were better suited. However, none of them eradicated completely.

(ii) The phenomenon well-represented by Darwin’s finches other than natural selection is adaptive radiation.
Adaptive Radiation: HF Osborn (1898) developed the concept of adaptive radiation or divergent evolution. It involves the development of different functional structures from a common ancestral form.

When a group of organisms shares a homologous structures, which are specialised to perform a variety of different functions, it shows adaptive radiation. This represents the evolution of new forms in several directions from the common ancestral type (divergence).

The significance of adaptive radiation is that it suggests the existence of divergent evolution based on the modification of homologous structures. The examples of divergent evolution are as follows:
(a) Darwin’s finches of Galapagos Islands had common ancestors. Later on, their beaks modified according to their feeding habits.
(b) Australian marsupials and limbs of mammals are also good examples of adaptive radiation.

Question 79.
(i) How did Darwin explain adaptive radiation? Give another example exhibiting adaptive radiation.
(ii) Name the scientist who influenced Darwin and how? (All India 2016)
Answer:
(i) Refer to Answer No. 27 of Topic 1.
(ii) Darwin was influenced by Thomus Robert Malthus, a British economist. He put forward a theory of human population growth. He wrote the book ‘An Essay of the Principles of Population’.

Question 80.
(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. (Delhi 2016)
Answer:
(i) Refer to Answer No. 27 of Topic 1.
(ii) Refer to Answer No. 32 of Topic 2.

Question 81.
Anayaa told her younger brother that forelimbs of man and cheetah are structurally similar, though they perform different functions.
Do you agree with Anayaa? Give an example of such organs from the plant world.
Answer:
Yes, I agree with Anayaa. Such organs are called homologous organs. Thorns of Bougainvillea and tendrils of Cucurbita are homologous organs in plants.

Question 82.
Anita and Sunita had a hot argument whether or not life is still originating on the earth today.
(i) As a student of biology what is your answer to the above problem and why?
(ii) What would have been the energy source for origin of life on the earth?
Answer:
(i) There is no origin of life on earth today because the atmosphere is oxidising and any new molecule if formed will get oxidised.
(ii) Sunlight (UV rays) and lighting electrical discharge would act as the energy source for origin of life on earth.

Question 83.
During the biology lecture on theories of evolution, Mrs. Sharma was teaching the topic Lamarckism. Kapil was in a confused state after the lecture, so he went to his teacher and asked his doubts. He asked that if characters can pass to next generation, why he does not have the tatoo that his mother has on her arm.
The teacher smiled and told him the actual fact about it. She also explained him the reasons for the rejection of Lamarck’s theory.
(i) Name the book in which Lamarckism was explained.
(ii) What are the three postulates of this theory?
(iii) What are the values shown by teacher?
Answer:
(i) Philosophic Zoologique in 1809.

(ii) three postulates of this theory are:

• New needs in respect to changing environment.
• Acquisition of characters.
• Inheritance of acquired characters.

(iii) The teacher was patient, knowledgeable and understanding.