ICSE Class 12

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 Multiple Choice QuestionsLong Answer Type



(a) Explain the basic postulates of Darwinism.

(b) What is genetic erosion? State any two factors responsible for it.

(c) What is meant by biotic potential?


(a) Basic postulates of Darwinism:

(i) All living beings have an innate desire to produce its known progeny for the continuity of race. The productivity of all livings organism is far beyond the ultimate numbers which can possibly survive. The space and the available food supply is limited but the number of organism increases in a geometric ratio.

(ii) Struggle of existence : Since the number of individuals produced is far more than the number that can be supported, there is an everlasting competition between organisms at all levels of life. Thus there is struggle for their existence and this struggle may be of the following three types.

(iii) Variations under nature : No two individuals of a species are exactly similar and they have some differences. These differences are called variations and without variations evolution is not possible. Variations give rise to new characters and heredity passes them on to the next generation.

(iv) Natural selection or survival of the fittest : Due to struggle for existence and useful heritable variations, only those individuals survive which are best fitted to new conditions of life. The individuals which survive show high selective value and in the course of time they develop various adaptive modifications to suit the changed conditions of life. Such selection was called natural selection by Darwin.

(v) Origin of species : In the course of long periods of time the best fitted and suitable individuals survived and became adjustment to the nature. As environment is ever changing, further changes occur and thus new adaptations appear in organisms. The later descendants after several generations become quite distinct from their ancestors. In this way new species appear.

(b) Genetic erosion is a process whereby an already limited gene pool of an endangered species of plant or animal diminishes even more when individuals from the surviving population die off without getting a chance to meet and breed with others in their endangered low population. The replacement of traditional and local crops and farm animals with more genetically uniform, modern varieties has caused the genetic erosion of crops and livestock species around the world.


(c) Biotic potential is the ability of a population of living species to increase under ideal environmental conditions – sufficient food supply, no predators, and a lack of disease. An organism's rate of reproduction and the size of each litter are the primary determining factors for biotic potential. Biotic potential is the potential for life, or how fast a species reproduces when not limited by its environment.



(a) Explain the origin of bread wheat (Triticum aestivum)

(b) Write two differences between;

(i) B cells and T cells (ii) Antibiotics and Interferons

(c) Define organ transplantation. Mention a precaution which must be taken for this procedure.