Class 12 Biology Chapter 7 Evolution The answer to each chapter is provided in the list so that you can easily browse through different chapters Assam Board HS 2nd Year Biology Chapter 7 Evolution Question Answer.
Class 12 Biology Chapter 7 Evolution
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III. Question for 3 Mark :
Short type Questions :
Q.1. “Embryology provide evidences of organic evolution’. Explain.
Ans : Amongst the evidences of organic evolution, the embryological evidences are found to be most conclusive. If we study the developmental stages from eggs then we will find some similarities in their development than to the adult. Fog example, the study of embryo of fish, frog, lizard, birds, mammals revels that after fertilization, zygote is formed and which is followed by a series of cleavage. The zygote is now called as mórula which is common to all. Again it follows blastula and gastrula stage which is also common to all. The embryo is showing the aquatic mode of life and we can conclude from this study, that all the vertebrate animals are coming from aquatic mode of life. Ontogeny recapitulates phylogeny is widely accepted.
Q.2. Distinguish between :
(a) Homologous organ and Analogous organ.
Ans : Homologous organs are those which show varied function but are structurally similar and have common origin. For example the wing of birds, forelimb of human, forelimb of horse, flipper of whale are all functionally different but structurally and from the point of origin are similar. Analogous organs are functionally similar but structurally dissimilar and from the point of origin also different. For example the wings of butterfly and the wings of bat are functionally similar but have different origin and structure.
(b) Convergent and Divergent evolution.
Ans : Homologous organs show trend of convergent evolution. The forelimb of human, forelimb of horse, the flippers of whale, the wings of bat are all structurally similar and have common origin. But due to change of environment, food, survival strategy these organs have undergone modification and other hand, Analogous organs though structurally and from the point of origin are different but have to perform similar function. The wings of bat and the wings of butterfly, flipper of dolphins, the wings of penguin are such structures. These are example of divergent evolution.
Q.3. Describe briefly about Lamarckism.
Ans : Jean Baptist de Lamarck (1744-1829) proposed an explanation of evolution in 1809. He was a French biologist . His theory was known as theory of inheritance of acquired characters or popularly known as Lamarckism. This scientifically propounded theory of organic evolution was first published in his book “Philosophic Zoologique” in 1809. Although the validity of Lamarckism was questioned by others in later period, it was regarded as the first scientific basis of explanation of evolution that occurs in all forms of life.
Lamarck laid down certain factors which govern the process of organic evolution.
These factors are :
(i) Influence of environment.
(ii) Use and disuse of organs.
(iii) Inheritance of acquired characters.
The environment in which the organisms live influences the life processes of the individual. The environmental change leads to the change of the habit of the organism. The change of habits result into the change of the structures of the body. A particular environment requires greater use of a particular organ or it may require the use of an organ which is not essential in the former individuais. Environment has influence on the morphological characters of an organism which may be later transmitted to the next generation.
According to Lamarck the structure and development of an organ depend on the use of this organ or system. Continuous use of a particular organ to adapt in a particular environment enhances the size and efficiency of this organ. Continuous disuse of an organ leads to its reduced efficiency and size and ultimately it disappears. Such changes in structure during the life time of a particular organism is known as an acquired character. The acquired characters become genetical character and inherited from one generation to the next generation.
Q.4. Do mutation has any significance in evolution? Explain.
Ans : Hugo de vries (1840-1935) was a dutch botanist who coined the 4. word mutation in 1901.
Mutation is a sudden heritable phenotypic change independen of the environmental influence de vries studied the different types of ornamental garden plants called oenothera lamarckiana (evening primrose). de vries observed that all the plants of this species were not the same. Some were different from the others. He noted two new types and named oenothera bevistylis and oenothera longifolia each of which breed true from seed. The original species oenothera lamarckiana and these two new types were then cultured in the botanical garden of Amsterdam de Vries found that several new kinds which can be regarded as new species occurred in the following generations. These new species difference markedly from the next. These new types breed true and were called mutants devries observed that the new species occurred in his culture might be due to some sudden herit able changes.
From the above observation he stated that new species appeared as a result of sudden discontinuous variations rather than by slow but gradual variations. As the mutations were of random occurrence, evolution was also considered to that at random. de Vries was of the opinion that mutants appear from time to time which show gametes are somewhat different from the usual ones of a particular species. Though the mutation theory of de Vries was accepted by magi workers but he could not explain why mutation occur.
Studies on mutation were undertaken by many workers later. The idea of mutation put forwarded by de Vries was found to be different from the present day explanation of mutation. Later studies showed that new types described by de Vries were not true mutants. Latest study reveals that true mutation brings changes in the gene level. Hence genetic characters are changed. The mutation which is found in gametes or genetic level are inherited. The occurrence of true mutation is extremely rare.
Q.5. Discuss the Modern synthetic theory.
Ans : The basic concept of modern synthetic theory is based on Dobzhansky’s (1937) book Genetic and origen of species. The name modern synthetic theory term was given by Julian Huxley is 1942. Many scientists consider Neo-Darwinism as the modern synthetic theory of evolution.
According to those scientists there are different factors which influence the process of organic evolution.
(i) Basic Factors :
(a) Gene mutation.
(b) Change in chromosome structure and number.
(c) Genetic recombination.
(d) Natural selection.
(e) Reproductive isolation.
(ii) Accessory Factors :
(a) Gene migration.
(b) Hybridization.
(c) Genetic drift.
Out of all the 5 basic factors, the first three factors are necessary to develop genetic variations while last two provides the direction to the process of organic evolution.
Q.6. What is adaptive radiation? Give examples.
Ans : The process of evolution of different species in a given geographical area starting from one point and rediating other areas of geography or habitats is called adaptive radiation. Darwin’s finches represent a good example of this phenomenon. Different types of movements in placental mammals and Australian marsupials are other examples. no slt Elephants and tigers are mainly found in Africa and India.
Q.7. List any two factors which could upset the genetic equilibrium of a population.
Ans : According to Hardy-Weinberg’s principle the gene frequency in a population remains unchanged. Genes may flow within the population but the overall gene frequency will remain the same. This is called genetic equilibrium. Genetic equilibrium may be disturbed by two factors only. One, due to mutation and the other due to genetic drift. In an extremely small population repeated interbreeding involves the same gene pool. There is no chance of inflow of new genes. Moreover, there is sufficient chance that none of the individuals carrying a particular allele may mate and reproduce successfully.
The progenies of these individuals will be totally devoid of that particular allele. In this way many alleles may be lost gradually from the population or particular alleles may proportionately increase. Such variation in gene frequency is called genetic drift. As genetic drift causes loss of variability, it has no significance in progressive evolution. However, genetic drift increases variability within species and hence the chance of their survival under changed environment is brighter than a larger population.
Q.8. Why are the wings of a butterfly and that of a bat called analogous?
Ans :The wings of butterfly and wings of bat are termed as analogous. As we knew that the organs which may have different structure or origin, but performing the similar mode of function then it is called as analogous. The structure of bat is not similar to the structure of butterfly and they have different origin of their wings. But in both the cases wings are used to perform the same function i.e. fight hence analogous.
Q.9. “The evolutionary story of moths in England during industrialization reveals that evolution is apparently reversibles’ Discuss.
Ans : In pre-industrial era moths of England were white. They used to rest in trees having lichen which were white. Thus they could avoid detection by birds. But during industrial revolution lichens had vanished due to smoke and dust. The moths then could not hide themselves from predator. As a result they gradually changed their colour from white to blackish so that if they rest on the trunk of licken less trees they could not be detected easily. This is a kind of reversible evolutionary exercise.
Q.10. Discuss briefly the experiment of Miller.
Ans : A number of theories were put forwarded by a number scientists to demonstrate the process of evolution of life. Out of Stanley Miller and Harold Urey is 1953 demonstrated an experiment to establish the chemical origin of life.
They tried to create and atmosphere in the laboratory which might have been existed in the primitive earth. High intensity electric sparks were passed through a mixture of water vapours, methane, ammonia and hydrogen gases which were thought to have constituted the primitive atmosphere (taken in a closed vessel). As a result various organic compounds were formed including the amino acids. The mixture was allowed to stand for several weeks. The solution was then chromatographed. Miller could detect several organic compounds including both carbo-hydrates and amino acids, like glycine and alanine etc. in the mixture. For (1955), Palim and Calvin (1962) and many other were also successful in synthesizing the organic compounds in the laboratory following Miller from the similar elements which probably constituted the primitive atmosphere.
Q.11. What is natural selection? Elucidate two different effects of natural selection on variation of organisms.
Ans : The process by which comparatively better adapted individuals out of a heterogenous population are favoured by nature over the less adapted individuals is called natural selection.
(a) Natural selection causes the progressive changes in gene (v) frequencies i.e. The frequency of adaptive gene increases while the frequency of less adaptive gene decreases.
(b) Those individuals, which are best adapted to the environment, survive longer and reproduce at a higher rate and produce more offsprings rate and produce more offsprings than those which are less adopted.
Q.12. What do you mean by speciation? Name the different form of speciation.
Ans : The origin of a new species from pre-existing species in called the speciation.
The speciation is of the following types:
(A) Gradual Speciation : It is the gradual divergence of population due to the accumulation of variations. It is of two types:
(i) Allopatric Speciation : When an original population becomes separated spatially because of geographic barrier, into two or more groups, then it is called allopatric speciation e.g. Darwin’s finches of Galapagos.
(ii) Sympatric Speciation : It occurs within same geographical area stand within original population and reproductively isolated.e.g pig frog and Gopher frog.
(B) Abrupt speciation : Sudden development of a species is called abrupt speciation. It is of two tipes –
(i) Mulation : Mutation can produce the Libling species which are morphologically similar but ecologically and reproductively isolated eg. Drosophila pseudoobscura and D. Persimilis.
(ii) Hybridization : It is caused by hybrid. e.g. Rapheno brassica.
| Sl. No. | CONTENTS |
| Chapter 1 | Reproduction in Organisms |
| Chapter 2 | Sexual Reproduction in Flowering Plants |
| Chapter 3 | Human Reproduction |
| Chapter 4 | Reproductive Health |
| Chapter 5 | Principles of Inheritance and Variation |
| Chapter 6 | Molecular Basis of Inheritance |
| Chapter 7 | Evolution |
| Chapter 8 | Human Health and Disease |
| Chapter 9 | Strategies for Enhancement in Food Production |
| Chapter 10 | Microbes in Human Welfare |
| Chapter 11 | Biotechnology: Principles And Processes |
| Chapter 12 | Biotechnology and its Applications |
| Chapter 13 | Organisms and Populations |
| Chapter 14 | Ecosystem |
| Chapter 15 | Biodiversity and Conservation |
| Chapter 16 | Bioresources of Assam |
| Chapter 17 | Environmental Issues |
Q.13. In what sense mutation explained by Hugo-de-vries are different from Darwinian variations.
Ans : The followings are the reasons for which mutation is different from the Darwinian variation.
(a) Mulation is a sudden change process which is abruptly taking place while the Darwinian variation process.
(b) Mulation creat and maintain variation within the population is not found in Darwinian variation.
(c) In mutation chromosomal make up, genetic combination may change but in Daminian variation, shape size and colour may changed.
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