Case study (4 Marks)

Question 14 Marks

Read the following text carefully and answer the questions that follow:
The diagram shows the replication of the retrovirus in the host.

i. Fill in the missing data in boxes labelled 1 & 2. (1)
ii. Why is it named as retrovirus? (1)
iii. While the virus is being replicated and released, does the infected cell survive and why the virus infected cells prevent spreading of virus to healthy cells? (2)
OR
What is the effect of HIV infection on immune system? (2)

Answer

i. 1. Viral DNA is produced by reverse transcription.
2. New viral RNA is produced by the infected cell.
ii. HIV has RNA genome; it produces DNA by reverse transcription.
iii. Infected cell can survive and by releasing alpha-interferon.
OR
Due to HIV infection immune system gets suppressed as decrease in T-lymphocytes occurs.

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Question 24 Marks

Read the following text carefully and answer the questions that follow:
The following is the illustration of the sequence of ovarian events (A-I) in a humans female.

i. Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents. (1)
ii. Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event. (1)
iii. Explain the changes that occur in the uterus simultaneously in anticipation. (2)
OR
Write the differences between C and H. (2)

Answer

i. Figure F illustrates ovulation. It represents the ovulatory stage of oogenesis.
ii. Ovarian and pituitary hormones involved in causing ovulation are
Ovarian hormone Estrogen.
Pituitary hormone LH and FSH.
iii. In anticipation of receiving the fertilised egg, the endometrium of the uterus gets thickened and also the blood supply to the endometrium increases.
OR
The figure C stage represents the secondary follicle and the H stage represents the degenerating corpus luteum.

Secondary follicle	Corpus luteum
It is surrounded by layers of granulosa cells and theca layer.	Layers of granulosa cells and theca cells are absent.
It contains an oocyte in the developing stage.	It does not contain oocyte as it is formed after the release of secondary oocyte.

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Biology Case study (4 Marks)

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