IB Biology SL C3.2 Defence against disease questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceMedium1 mark

A patient is diagnosed with a viral infection, and an antibiotic is considered. Which explanation accounts for why the antibiotic will not control the infection?

Show answer and explanation

Answer: B. Antibiotics block processes that occur in bacteria but not in eukaryotic cells. Viruses rely on host-cell processes to reproduce, so they do not carry out the bacterial processes targeted by antibiotics.
A: correctly identifies viral reliance on human cells, but incorrectly claims the antibiotic target is shared with human cells.
C: identifies the bacterial target, but incorrectly states that viruses reproduce independently of host cells.
D: correctly describes viral reliance on host cells, but reverses the selectivity of antibiotics.
Remember: antibiotics target bacterial processes, not viral reproduction in host cells.

Question 2

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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