IB Biology SL C3.2 Defence against disease questions

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Question 1

Paper 2Medium16 marks

A group of 100 people with HIV was followed from the time their infection was confirmed. Researchers recorded the mean count of a particular type of lymphocyte and the percentage of participants who had at least one opportunistic infection.

Years after HIV infection was confirmedMean lymphocyte count (cells per μL)Participants with at least one opportunistic infection (%)
09002
36906
642024
918050
(a)

Calculate the percentage decrease in mean lymphocyte count between year 0 and year 9.

[3]
(b)

Describe the changes in both measurements between year 0 and year 9, using the data.

[4]
(c)

Identify the type of lymphocyte infected by HIV and state what HIV does to these cells.

[2]
(d)

Explain how the decline in these lymphocytes can lead to AIDS.

[3]
(e)

Explain two mechanisms by which HIV can be transmitted in body fluids: one involving blood and one during sexual intercourse.

[4]

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