NCERT Solutions for Class 12 Science Biology Chapter 7 - Evolution

Answer:

Lichens can be used as an atmospheric pollution indicator as they do not grow in areas that are polluted. They are sensitive to SO₂ pollution, hence unstable to synthesize organic food and do not grow well.

Hence, the correct answer is option (b).
 

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Theory of spontaneous generation stated that life can arise from non-living things only. It is also called theory of abiogenesis. Louis Pasteur disapproved this theory and demonstrated that life arose from living forms.

Hence, the correct answer is option (c).

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Animal husbandry and plant breeding are the examples of artificial selection. It is a process in which the breeder choose to perpetuate only those forms that have certain desirable inheritable characteristics.

Hence, the correct answer is option (b).

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Palaeontological evidences for evolution refer to the fossils. Fossils are the preserved remains or traces of organisms from the distant past. The study of fossils is called Palacontology.

Hence, the correct answer is option (c).

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The bones of forelimbs of whale, bat, cheetah and man are similar in structure, because they have a common ancestor. These are homologous organs which have different functions across diverse forms, but are developed along same pattern.

Hence, the correct answer is option (b).

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Analogus organs have different structure (origin) but have similar functions. These organs arise due to convergent evolution.

Hence, the correct answer is option (d).

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(p + q)² = p² + 2pq + q² = 1 represents an equation used in population genetics. This equation is known as 'Hardy-Weinberg Principle'. This principle says that allele frequencies in a population are stable and is constant from generation to generation, i.e. the gene pool remains constant.

Hence, the correct answer is option (a).

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Appearance of antibiotic resistant bacteria is an example of pre-existing variation in the population.
Hence, the correct answer is option (c).

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Evolution of life shows that life forms had a trend of moving from water to land. The early vertebrates were fishes (which lived only in water). Some fishes gradually changed into amphibians. Certain amphibians transformed into reptiles. Then some transformed into birds and then mammals.

Hence, the correct answer is option (d).

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Viviparity is considered to be more evolved because the young ones are protected inside the mother's body and are looked after they are born leading to more chances of survival.

Hence, the correct answer is option (c).

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Fossils are generally found in sedimentary rocks, which are formed by gradual deposition of silt, sand and calcium carbonate over millions of years in regions such as lakes or sea during their formation.

Hence, the correct answer is option (a).

Answer:

The expected frequency of MN blood group bearing organisms is likely to be 42%.
According to Hardy-Weinberg equation, p² + q² + 2pq = 1.
where, p = frequency of M alleles = 0.7
p² = frequency of homozygous dominant individuals = 0.49
q = frequency of N alleles = 0.3
q² = frequency of homozygous recessive individuals.
2pq = frequency of heterozygous individuals
So, (0.7)² + (0.3)² + 2pq = 1
      0.49 + 0.09 + 2pq = 1
2pq = 0.42 = Frequency of heterozygous individual i.e. 42%.

Hence, the correct answer is option (a).

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Directional selection is observed in moth. Under this, individuals at one end of the frequency distribution do well light and so more individuals of that type will be present in next generation.

Hence, the correct answer is option (b).

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Human evolution started from Ramapithecus about 14-15 mya. Then about 2 mya Homo habilis appeared. Then the Homo erectus and around 10,000 years ago modern man appeared.

Hence, the correct answer is option (c).

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Lobe fish is an example for link species because it belongs to bony fishes and show characters from other two groups of animals.

Hence, the correct answer is option (a).

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Darwin is related with evolution by natural selection. Oparin put forth abiogenesis theory, which states that life originated from non-living things.
Lamarck is related to use and disuse of organs. Wagner proposed continental drift theory.

Hence, the correct answer is option (b).

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In 1953, Miller created an experimental set up to prove the occurrence of chemical evolution by stimulating hypothetical conditions present on earth. These conditions include high temperature, volcanic storms and reducing environment containing CH₄, (methane), NH₃ (ammonia), hydrogen (H₂) and H₂O (water). 

Hence, the correct answer is option (d).

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Variations during mutations of meiotic recombinations are random and directionless. Hugo de Vries based on his work on evening primrose stated that it is mutation which causes sudden appearance of variations that results in speciation. Mutations are sudden, heritable and persistent in successive generation.

Hence, the correct answer is option (a).

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The organisms with hard parts are likely to be fossilised, then those who do not have such parts. Fossils are remains of hard parts such as bones, teeth etc. of life forms which may be found in rocks.

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Yes, aquatic life forms get fossilised, there are more aquatic than terrestrial fossil organisms. They are found in the sediments of the water bodies. Later, sediments form the part of sedimentary rocks in which fossils are deposited.

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When we say simple organisms and complex organisms, then we are classifying organisms according to their evolutionary history. Simple organisms refers to primitive that has simple structural and functional organisation. On the other hand, complex organisms refers to more evolved and forming complex level of structural and functional organisations.

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Age of a living tree can be estimated by
(i) Counting the number of annual rings present in the trunk of the tree.
(ii) Comparing the diameter of the trunk of the tree with an average growth factor of that tree.
(iii) The help of radioactive carbon dating.

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The presence of wings in birds and butterfly is considered to be due to convergent evolution, and they are adapted for flying. Convergent evolution forms analogous organs.

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The age of a fossil can be calculated by radioactive dating. It is done by comparing the naturally occurring radioactive isotope with its decay products using known decay rates.

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The most important pre-condition for adaptive radiation is a geographic barrier or an isolated habitat.

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The age of rock can be estimated by natural radioactive decay of certain elements such as uranium-lead dating, potassium-argon dating etc.

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Functional macromolecules such as proteins enzymes, hormones, receptors, antibodies are evolving towards creation of a complex organism. These similarities are considered to share the same ancestory. For example: genetic code is nearly same to all life forms, from bacteria to archaea or animals and plants.

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Frequency of B allele = $\mathrm{BB}+\frac{1}{2}\mathrm{Bb}$

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The other two factors that affect Hardy-Weinberg equilibrium are natural selection and mutation.

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Founder effect is the phenomenon that occurs when a small group of organisms becomes isolated from a larger population and becomes so genetically different from the original population that they become a new population altogether.

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Ramapithecus was more man-like, who walked erect on its hind legs, while Dryopithecus was more ape-like with same length of arms and legs.

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The first hominid was known by the latin name Homo habilis. Their brain capacitias were between 650 - 800 cc. They probably did not eat meat.

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Homo habilis did not eat meat. This creature was the first human like being with brain capacities between 650-800 cc.

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Yes, we can correct this as life evolves from pre-existent life. The first life that appeared on earth was apparently the result of chemical evolution, i.e. the life originated from inorganic molecules which formed organic molecules, further forming complex compounds.
This finally resulted into simple cells and then simple organisms, wherein complexity development with time. However, once life originated, abiogenesis could not follow and hence life evolved further only through abiogenesis.

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Yes, a natural disaster such as an earthquake can be the cause of extinction of species. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. Scientists have believed that volcanic eruptions, large asteroids and meteor struck the earth caused widespread destruction and the extinction of dinosaurs.

Answer:

Nascent oxygen is highly reactive and can easily react with variety of biomolecules, including DNA and proteins. Nascent oxygen is a permanent oxidising agent. It is thus considered to be toxic to aerobic life forms if it reacts with DNA, it will lead to mutations and defective proteins. It reacts with enzymes, and degrade many metabolic pathways and processes.

Answer:

The creation and presence of variations is directionless in regard that they occur randomly and spontaneously. The variations which are helpful in the adaptations of an organism towards its surroundings would be passed on to next generations.
Natural selection is the most critical evolutionary process which can be considered directional as it leads to only one path that is selection and perpetuation of better adapted individuals. Natural selection leads to survival of the fittest and disappearance of all those organisms which do not all fit in the prevailing environmental conditions.

Answer:

In England, before Industrialisation the white winged moths were able to thrive because whitish lichens and moss flourished on tree trunks. White winged moth blended very well and therefore had better chances of survival against the whitish background. But when the industrial revolution started the tree trunks turned dark. Lichens and mosses did not survive. As a result, the population of white winged moth decreased and the population dark winged moth increased. Thus, evolution of white winged moth reversed due to industrialization.

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Evolution helps us to understand the history of life. We can view evolution as a pattern of evolutionary change and as a process as well. The world we see, all the inanimate and animate, is only the success stories of evolution. When we describe the story of this world, we describe evolution as a process. On the other hand, when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection. Natural selection is the outcome of favourable variations among organisms and environmental conditions.
Thus, we are still not clear whether to regard evolution and natural selection as processes or end result of processes.

Answer:

Three factors affecting allele frequency in populations are:-
(1) Mutations - These are sudden inheritable changes which are supposed to be the primary source of genetic variation. They randomly occur in all directions.
(2) Gene Flow - It is the movement of alleles into and out of a gene pool. Breeding of immigrants with the host population adds new alleles to the gene pool of the host population.
(3) Genetic Drift - If the movement of alleles into a gene pool or out of gene pool takes place by chance, it is called genetic drift.

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Yes, gene flow occurs through generations through geographical barrier. By studying specific allelic frequencies in a different populations of the world, we can predict human migratory patterns in pre historic and historic area.
Studies have used specific genes/chromosomes/mitochondrial DNA to trace the evolutionary history and migratory patterns of humans.

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Race - It is a classification system to categorise group of people that share similar and distinct physical characteristics. Members of different races of same species can interbreed.

Breed - It is a group of animals or plants that have the similar appearance, characteristics or behaviours that distinguish it from other animals or plants of same species.

Cultivars - A group of plants that have been selected for desirable characteristics which can be raised through vegetative propagation.

Variety - Variety is similar to race but it includes plants. It is a taxonomic category that ranks below species level in plant kingdom.

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"survival of the fittest" means those who survive are fit. Individuals that have more favourable variations will survive and reproduce in that environment compared to those who have less favourable variations.

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Characteristic criteria for designating a Mendelian population are
(i) Population must be sufficiently large.
(ii) Population must have the potential for a free flow of genetic material among individuals through sexual reproduction.
(iii) Migration should be negligible/nill in the population.

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Migration is the movement of individuals from one place to another. Migration can be the movement of individual in or out of the population. Migration may bring more such alleles whose effects are selected by the nature. Thus enhancing the effect of selection.
Similarly, migration may lead to removal of alleles whose effects are not selected by the nature thus blur the effects of selection.

Answer:

Hardy-Weinberg principle states that the sum of allelic frequencies in a population remains constant.
According to him, the frequency of occurrence of alleles of a gene in a population remains constant through generations unless disturbances such as mutations, non-random mating, etc. are introduced.
Genetic equilibrium (gene pool remains constant) is a state which provides a baseline to measure genetic change. Sum total of all allelic frequencies is 1. Individual frequencies are represented as p and q such as in a diploid, where p and q represent the frequency of allele A and a. The frequency of AA is p², that of aa is q², and that of Aa is 2pq.
Hence, p² + 2pq + q² = 1, which is the expansion of (p + q)².

Hardy-Weinberg equilibrium is affected by-

• gene flow or gene migration
• genetic drift (changes occurring by chance)
• mutation
• genetic recombination
• natural selection

Answer:

In divergent evolution, two species share common ancestors, but due to environmental changes, they develop distinct features that result in the emergence of new species. Changes in abiotic factors (such as temperature, pH, sunshine intensity, etc.) or biotic factors (living components of the ecosystem) can lead to divergent evolution.
The adaptations to a new home and shifting environmental conditions are driving the diverse evolution.

Answer:

In the post-industrial era in England, because of the rising pollution, the lichens did not survive. The tree trunks were darkened with soot. If the factories had been eliminated, the pollution would have decreased, allowing lichen to regrowth and an increase in the population of white-winged moths.

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Darwin's theory of Evolution

• According to Darwin, evolution took place by natural selection.
• The number of life forms depends upon their ability to multiply and their life span.
• Another aspect of natural selection is the survival of the fittest, where nature selects the individuals, which are most fit, to adapt to their environment.
• Branching descent and natural selection are the two important concepts of Darwin’s theory of evolution.
• Darwin also observed that variations are inheritable and the species fit to survive the most, leaves more offspring. Hence, the population’s characteristics change, giving rise to the evolution of new life forms.

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Convergent evolution is observed among two creatures living in the same region. They profit from their ability to adapt to their surroundings. For instance, drought-resistant desert plants such as agave, aloe, and orchids store water and mucilage. despite having different morphologies. 

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The process of evolution is dynamic and it occurs constantly. Humans play a part in this process, too. For example,

• Milk and other lactose-containing products were not previously ingested by humans, but today they are consumed by people everywhere.
• The population in malaria-prone areas has undergone another evolutionary transition. They developed sickle cell anaemia as a defence against parasites that cause malaria.

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The theory of natural selection has been attributed to Darwin. He was unaware of the origin of these variations. He was aware of Mendel's findings. Darwin ignored the inheritable ‘factors’ influencing the phenotype of Mendel and he would have been able to explain the origin of variation. Both Mendel and Darwin were unaware of the fact that genes were playing an important role in their theories. Darwin claimed that changes were happening and accumulating, so the possibility of Darwin explaining the source of variation is high.