Case study (4 Marks)

Question 14 Marks

Read the following text carefully and answer the questions that follow:
A lymphocyte isa type of white blood cell. Enlarge. Blood cells. Blood contains many types of cells: white blood cells (monocytes, lymphocytes, neutrophils, eosinophils, basophils, and macrophages), red blood cells (erythrocytes), and platelets. Blood circulates through the body in the arteries and veins.

i. Why are the antigens called antibody-generating chemicals? (1)
ii. Which two types of lymphocytes are involved in immunity? (1)
iii. Give the common site of formation of two types of lymphocytes. (2)
OR
What is the site of differentiation of two types of lymphocytes? (2)

Answer

i. The antigens called antibody-generating chemicals because a specific antigen stimulates the production of specific antibody.
ii. B-lymphocytes and T-lymphocytes are involved in immunity.
iii. Haemocytoblasts or stem cells of bone marrow are the common sites of formation of two types of lymphocytes.
OR
B-lymphocytes differentiate in Peyer's patches, tonsils and appendix of mammals and bursa of Fabricius in the birds. Tlymphocytes differentiate in the thymus gland.

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Question 24 Marks

Read the following text carefully and answer the questions that follow:
The process of formation of a mature female gamete is called oogenesis which is markedly different from spermatogenesis. A schematic representation of Oogenesis is shown below study the flow chart carefully.

i. How is a primary oocyte different from a secondary oocyte? (1)
i. Mention the changes taking place during the transition of a secondary follicle to Graafian follicle in the oogonia. (1)
iii. How many primary follicles are left in each ovary in a human female at puberty? (2)
OR
What happen to graafuan follicle after ovulation? (2)

Answer

i. The primary oocyte is a diploid cell whereas secondary oocyte is a haploid cell. The primary oocyte is formed when oogonia are at the prophase-I of the meiotic division in the foetal ovary whereas secondary oocyte is formed from primary oocyte after meiosis – I division to produce ova in females during the stage of puberty.
ii. The secondary follicle is then transformed into a tertiary follicle characterized by antrum, which is a fluid-filled cavity. At this phase, the primary oocyte grows in size inside the tertiary follicle to complete the first meiotic division. The tertiary follicle finally transitions to form the Graafian follicle.
iii. large number of primary follicles degenerate in females during the period from birth to puberty by the process called follicular atresia. As a result, about 60000-80000 primary follicles are left in each ovary at puberty.
OR
After ovulation, the remaining cells of Graafian follicle are stimulated by LH to develop corpus luteum (an endocrine gland which secrete progesterone hormone).

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Biology Case study (4 Marks)

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