CBSE Class 12 Biology Evolution Worksheet Set B

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

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

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

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

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

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

Question. How do Darwin’s finches illustrate adaptive radiation?
Answer. Process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation. Darwin’s finches represent one of the best example of this phenomenon, as many varieties of finches were observed to be present in the same island. All the varieties, evolved on the island itself from the original seed-eating finches that lead to various modifications in the finches according to their food habits. This evolution in finches enabled the birds to become insectivorous, vegetarian, wood pecking, ground feeding etc.

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

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

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

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

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

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

Question. How does a population become ‘founders’ of a new species?
Answer. When a few individuals or a small group of individuals from some large population invades a new or isolated geographical region, they may have different genotype frequencies from that of parent population, hence these become the founders or founder members.

Question. According to Hardy-Weinberg’s principle the allele frequency of a population remains constant. How do you interpret the change of frequency of alleles in a population?
Answer. Change of frequency of alleles in a population will result in natural selection leading to the evolution.

Question. What does the following equation represent? Explain.
p² + 2pq + q² = 1
Answer. The given equation represents Hardy-Weinberg equation.
frequencies in a population are stable and is constant from generation to generation. The gene pool (total genes and their alleles in a population) remains constant. This is called genetic equilibrium.
Hardy and Weinberg stated it using an algebraic equation.
Sum total of all the allelic frequencies is 1. Individual frequencies, for example, can be named p, q, etc. In a diploid, p and q represent the frequency of allele A and allele a respectively. The frequency of AA individuals in a population is simply p². The probability that an allele A with 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 is 2pq. Hence, p² + 2pq + q² = 1. This is a binomial expansion of (p + q)².
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.

Question. Describe the three different ways by which natural selection can affect the frequency of a heritable trait in a population.
Answer. Based upon different organism-environment relationships, following these different kinds of selection process have been recognised:
(a) Stabilising selection or Balancing selection: It favours the average or normal phenotypes and eliminates the extreme variants, that fall towards both ends of the bell-shaped curve of variability for the distribution of measurements of phenotypic traits.
(b) Directional selection or Progressive selection: It favours the phenotype which is extreme and then distribution curve of the population is pushed in that direction.
(c) Disruptive selection or Diversifying selection: The extremes have more adaptable phenotypes than the average ones. Consequently, the original population is disrupted into two more separate groups that later evolve into new species.

Question. Giving three reasons, write how Hardy- Weinberg equilibrium can be affected.
Answer. Hardy-Weinberg equilibrium can be effected by following ways:
(a) Gene flow : It refers to the movement of alleles from one population to another as a result of interbreeding between members of the two populations. It causes continual interchange of alleles between organisms.
(b) Genetic drift : It refers to a change in the population of alleles in the gene pool. It is random and occurs only by chance.
(c) Genetic recombination : Crossing over during meiosis is a major source of genetic variation within population. Alleles of parental linkage groups separate and new associations of alleles are formed in the gamete cells. Offspring formed from these gametes showing ‘new’ combination of characteristics are called recombinants.

Question. How is genetic drift different from gene migration? Explain
Answer. Genetic drift refers to the random fluctuations in the gene frequencies in a small population, generation after generation purely by chance.
Gene migration is the change in gene frequency in the original population and the new population, when a section of population migrate to another place or is added to a new population.

Question. Coelacanth was caught in 1938 in South Africa. Why it is very significant in the evolutionary history of vertebrates? 
Answer. Coelacanth is considered to be the missing link between fishes and the first four-limbed animals (amphibians). These were the ancestors of modern day frogs and salamanders.

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

Question. Discovery of lobefins is considered very significant by evolutionary biologists. Explain.
Answer. Discovery of lobefins is significant for evolution because lobefins (called coelacanth) evolved into the first amphibians that lived on both land and water. These were ancestors of modern day frogs and salamanders. The amphibians evolved into reptiles. They lay thick-shelled eggs which do not dry up in sun unlike those of amphibians.

Question. Name the ancestors of a man based on the features given below :
(a) Human like, meat-eater with 900 cc brain, lived in Java.
(b) More human with brain size 1400 cc, lived in Central Asia, used hides and buried their dead.
(c) Human like, vegetarian, with brain capacity between 650 cc and 800 cc.
(d) Man like primate, that existed about 15 mya. Fossils found in Tanzania.
Answer. (a) Homo erectus, (b) Homo sapines neanderthalensis, (c) Homo habilis, (d) Ramapithecus

Question. Mention any three characteristics of Neanderthal man that lived in near East and Central Asia.
Answer. Characteristics of Neanderthal man:
(i) They possess a brain capacity of 1400 cc.
(ii) They walked upright and had low brows, receding jaws and high domed heads.
(iii) They used hides to protect their body and bury their dead.

Question. (a) Name the primates that lived about 15 million years ago. List their characteristic features.
(b) (i) Where was the first man-like animal found?
(ii) When did modern Homo sapiens appear on this planet?
Answer. (a) Dryopithecus and Ramapithecus appeared about 14-15 million years ago.
(b) (i) Homo habilis were first man like animal and were discovered in East Africa.
(ii) Modern Homo sapiens appeared about 75,000-
10,000 years ago in holocene epoch.

Very Short Answer

Question. Who observed formation of amino acids?
Answer. S.L.Miller observed the formation of amino acids.

Question. What is evolutionary biology?
Answer. Evolutionary biology is the study of history of life forms on the earth.

Question. What are spores?
Answer. The units of life are called spores.

Question.Who proposed the first form of life from pre-existing non-living organic molecules?
Answer. Oparin and Haldane proposed the first form of life from pre-existing non-living organic molecules.

Question. Define founder effect?
Answer. The original drifted population becomes founders and the effect is called founder effect.

Short Answer

Question. What do you understand by evolution of life forms?
Answer. Evolution of life means the gradual formation of complex organisms from simpler ones.Evolution occurs when there is change in the genetic material the chemical molecule,DNA which is inherited from the parents, and especially in the proportions of different genes in a population. Genes represent the segments of DNA that provide the chemical code for producing proteins.

Question. What is embryology?
Answer. Embryology is the study and analysis of embryos. Evidence of an evolutionary common ancestor is seen in the similarity of embryos in markedly different species.

Question. What is meant by origin of life?
Answer. Origin of life means the appearance of simplest primordial life from non- living matter. Organic molecules are the necessary building blocks for the evolution of life. The Origin of Life, Oparin argued that a primordial soup of organic molecules could be created in oxygen-less atmosphere through the action of sunlight.

Question. What is the evidence of evolution?
Answer. Anatomy. Species may share similar physical features because the feature was present in a common ancestor (homologous structures). Molecular biology. DNA and the genetic code reflect the shared ancestry of life. Biogeography. Fossils. Direct observation.

Question. What do you mean by the embryological support for evolution?
Answer. Evidence of an evolutionary common ancestor is seen in the similarity of embryos in markedly different species. Darwin used the science of embryology to support his conclusions. Embryos and the development of embryos of various species within a class are similar even if their adult forms look nothing alike.

Long Answer

Question. State the difference between divergent evolution and convergent evolution? 
Answer. 1. Convergent evolution is a process by which distantly related species develop similar structures as adaptations to the environment whereas divergent evolution is a process by which an interbreeding species diverges into two or more descendant species.
2. Convergent evolution occurs through developing analogous structures whereas divergent evolution occurs through developing homologous structures.
3. In Convergent evolution both species live within the same environment whereas in divergent evolution the two species live in different environments than their ancestor.
4. In convergent evolution unrelated organisms evolve similarities while adapting to a common environment whereas in divergent evolution the divergence of two different species results in two species becoming less like the common ancestor.
5. Ostriches, rheas, and emus are examples of convergent evolution whereas dinosaurs, Darwin’s finches, and forelimb structures of vertebrates are examples of divergent evolution.

Question. Explain Hardy-Weinberg principle? 
Answer. Hardy- Weinberg principle stated that allele frequencies in a population are stable and is constant from generation. The gene pool and their alleles in a population remains a constant. Hardy-Weinberg principle stated it using an algebraic principle. Hardy- Weinberg law, an algebraic equation that describes the genetic equilibrium within a population. It was discovered independently in 1908 by Wilhelm Weinberg, a German physician, and Godfrey Harold Hardy, a British mathematician. There are five basic Hardy-Weinberg assumptions: no mutation, random mating, no gene flow, infinite population size, and no selection. Human populations do not meet all the conditions of Hardy-Weinberg principle exactly, and their allele frequencies will change from one generation to the next, so the population evolves. The Hardy-Weinberg Equilibrium can be used as a null hypothesis, compared to values from a real population, to describe statistically significant deviations from the Equilibrium. If the deviation is significant, then the gene frequencies are changing and thus, evolution is occurring. It is useful because it describes mathematically the genetic product of a population in which all individuals are equally likely to survive and to produce surviving offspring. Specifically, it calculates the genotype frequencies that will be observed in a population that is not evolving.

Question. State the difference between adaptive radiation and divergent evolution? 
Answer. 1. Adaptive radiation is the diversification of a group of individuals into forms filling different ecological niches whereas divergent evolution is a process of developing two or more species from a common ancestor over time.
2. Adaptive radiation is a rapid process of evolution whereas divergent evolution is a slow process of evolution.
3. Adaptive radiation is a type of microevolution whereas divergent evolution is a type of macroevolution.
4. Adaptive radiation brings morphological and ecological changes to a particular population whereas divergent evolution generates a new species that is unable to interbreed with the original species.
5. Darwin’s finches, Australian marsupials, and cichlid fish are some examples of adaptive radiation whereas the forelimb structures of mammals are an example of divergent evolution.

Question. Write short note on evolution? 
Answer. Evolution is the change in the characteristics of a species over several generations and relies on the process of natural selection. The theory of evolution is based on the idea that all species are related and gradually change over time. Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms and molecules. Evolution in organisms occurs through changes in heritable traits the inherited characteristics of an organism. In humans, for example: eye colour is an inherited characteristic and an individual might inherit the brown-eye trait from one of their parents. Inherited traits are controlled by genes and the complete set of genes within an organism's genome (genetic material) is called its genotype.

Question. State the difference between natural selection and artificial selection?
Answer. 1. Natural selection is the process whereby organisms better adapted to their environment tend to survive and produce more offspring whereas artificial selection refers to the process by which animals and plants are chosen by the breeder to produce desirable and inheritable characters in the successive generations.
2. Natural selection produces a huge biological diversity whereas artificial selection produces organisms with selected traits.
3. Natural selection is a nature-made selection process whereas artificial selection is a man-made selection process.
4. Natural selection is a slow process whereas artificial selection is a rapid process.
5. Natural selection facilitates evolution through generating biological diversity whereas artificial selection does not facilitate evolution.

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