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ISC Class 12 Biology Solved Question Paper 2010

Long Answer Type

31.

(a) Explain the basic postulates of Darwinism.

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

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32.
(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.

(a) Triticum aestivum is a cultigen (a plant that has been altered by humans through a process of selective breeding) and as such is only known in cultivation. First domesticated at least 9,000 years ago, its origins have been the subject of intensive botanical and genetic research.

Modern wheat cultivars belong primarily to two species: (1) hexaploid
bread wheat, Triticum aestivum (2n = 42 chromosomes), and (2) tetraploid,
hard or durum-type wheat, T. turgidum.

(b)

i.

B cells	T cells
Produce antibodies	Do not produce antibodies
Humoral immunity	Cell-mediated immunity

ii.

Antibiotics	Interferons
An antibody is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to identify and neutralize pathogens such as bacteria and viruses.	Interferons (IFNs) are a group of signaling proteins made and released by host cells in response to the presence of several pathogens, such as viruses and also tumor cells.
Produced by B cells	Produced by virus infected cells

(c) Replacement of diseased tissues or organs by healthy ones is called transplantation. This technique is increasingly used in surgery today. When a foreign tissue is inserted into or onto another individual it is rejected by the recipient because it acts as an antigen stimulating the immune response in the recipient. Before transplant, the surgeon must ensure that the transplanted organ would not be rejected by the recipient. This is done by ‘tissue matching’. Some immunosuppressant drugs like cortisol and cyclosporine are used to prevent rejection of transplants.

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