Directions : In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
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Assertion : Louis Pasteur showed that in flask open to air, new living organisms appeared in the heat killed yeast culture.
Reason : Life arise from pre-existing life.
(b) : Louis Pasteur, by careful experimentation, demonstrated that life comes only from pre-existing life. He observed that in presterilised closed flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’. He showed that the source of the new appearing microorganisms was the air and the organisms did not arise from the nutrient media.
Assertion : Primitive atmosphere was of reducing type.
Reason : First hydrogen atoms combined with all oxygen.
(a) : The interstellar dust from which earth originated was especially rich in hydrogen. It readily combined with nitrogen forming ammonia, with carbon forming methane, and with oxygen forming water leaving no free oxygen. Thus, early atmosphere of primitive earth was strongly reducing, it contained hydrogen, methane, ammonia and water vapours.
Assertion : Thorns and tendrils of Bougainvillea and Cucurbita represent homology.
Reason : Homologous organs have similar functions but are different in their structural details and origin.
(c) : The organs which have the same fundamental structure but are different in functions are called homologous organs. These organs follow the same basic plan of organisation during their development. For example, In plants, the homologous organs are thorn of Bougainvillea and a tendril of Curcurbita, both arising at the axillary position.
Assertion: Moths living in the industrial areas became dark to match body colour to the tree trunks.
Reason : Smoke from industries covered the tree, trunks, making them appear dark and helped dark moths to escape.
(d) : Industrial melanism is the increase of melanic (dark) forms of an animal in the areas of industrial pollution. The most
common example is of peppered moth which existed in two strains (forms): light coloured (white) and melanic (black). In the past, bark of trees were covered by whitish lichens, so white moths escaped unnoticed from predatory birds. After industrialisation lichens disappear due to pollution, so the white moths were selectively picked up by birds. But black moths escaped unnoticed so they managed to survive resulting in more population of black moths and less population of white moths. Thus, industrial melanism supports evolution by natural selection.
Assertion : Evolution is not a directed process in sense of determinism.
Reason : Evolution is a stochastic process based on chance events in nature and chance mutation in the organisms.
(a) : Evolution by anthropogenic action, such as excessive use of pesticides and antibiotics may lead to appearance of resistant organisms in a span of months and years, and not centuries. This shows that evolution is not a directed process, it is rather based on chance event and mutations occurring in nature and organisms respectively.
Assertion : The ernbryos of fish, salamander, tortoise, chick and a man, of same age resemble one another closely.
Reason : Ontogeny recapitulates phylogeny.
(a) : The early embryos in all the vertebrates exhibit remarkable similarity and it is not easy to differentiate a human embryo from the embryo of chick, lizard, frog or fish in early stages. This can be explained by ‘biogenetic law’ given by Haeckel. It says ‘ontogeny recapitulates phylogeny’. Ontogeny is the life history of the individual starting from ovum and phylogeny is the series of adult ancestors of the individual which must have incurred in the evolution of the group of this individual. It means that an individual during its development briefs its ancestral history.
Assertion : Darwin’s finches of Galapagos islands have different types of modified beaks according to their food habits.
Reason : Adaptive radiation, leads to development of different functional structures from a common ancestral form.
(a)
Assertion : Adaptive ability is inherited.
Reason : Fitness is the end result of the ability to adapt and get selected by the nature.
(b)
Assertion : Evolutionary trend is continuous changes of character in a lineage.
Reason : Lineage is an evolutionary sequence arranged in linear order.
(b) : The continuous change of the characters within an evolving lineage is called evolutionary trend. A lineage is an evolutionary sequence, arranged in linear order from an ancestral group to descendant group. A trend may be progressive (a general increase in size of organs) or rétrogressive (a general degeneration and loss of organs).
Assertion : Hardy-Weinberg principle explains the variations occurring in population and species over a number of generations.
Reason : Hardy-Weinberg principle is applicable in absence of genetic drift and gene flow.
(d) : The relative frequencies of various kinds of genes in a large and randomly mating, sexual panmictic population tend to remain constant from generation to generation in the absence of mutation, selection and gene flow. This is called Hardy-Weinberg principle or Hardy-Weinberg equilibrium. Genetic drift can cause elimination of certain alleles or fixation of the other in the population leading to a change in the population of alleles in the gene pool. So, genetic drift must not occur to maintain the equilibrium.
Assertion: Founder effect may lead to formation of new species.
Reason : Founders carry ail the parental gene pool to a new location.
(c) : When a few individuals or a small group of individuals from some large population invades a new or isolated geographical region, these become the founders or founder members. These founders carry on a limited portion of the parental gene pool. Their gene pool may contain certain alleles in a very low frequency or may lack a few alleles. The descendants of the founder, i.e., the founder population or marginal isolates in a new area will tend to have ratios similar to the founders rather than the source population. Sometimes they form a new species.
Assertion: Genetic drift refers to changes in the allele frequency occurring by chance.
Reason: Sampling errors often lead to the elimination of certain aileles and fixation of others, reducing genetic variability.
(b)
Assertion : Directional selection changes the population towards one particular direction.
Reason : This type of selection favours average sized individuals.
(c): Directional selection changes population towards one particular direction. It favours small or large sized individuals. Stabilising selection favours average sized individuals.
Assertion : Neanderthal man is the intermediate between Ramapithecus and Homo erectus.
Reason : Neanderthal man, with brain size of about 1400 cc., used hides to protect their body.
(d) : The Neanderthal man with a brain size of 1400 c.c. lived in near East and Central Asia between 1,00,000 – 40,000 years back. They used hides to protect their body and buried their dead. It is established that Neanderthal man appeared later than Ramapithecus and Homo erectus.
Assertion: The chimpanzee is the closest relative of the present day humans.
Reason : The banding pattern in some autosomes of man and chimpanzee is remarkably similar.
(a)
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