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Date November 2021 Marks available 1 Reference code 21N.1.SL.TZ0.26
Level Standard level Paper Paper 1 Time zone TZ0 / no time zone
Command term Question number 26 Adapted from N/A

Question

A person was infected with a pathogen and then later in life they were re-infected with the same pathogen. The graph shows the concentration of antibodies found in the blood that were produced in response to these two infections.

What is the reason for the faster rise in antibody concentration after the second infection?

A. The patient had previously been vaccinated with the antibody.

B. Antibodies had been stored after the first exposure.

C. Lymphocytes rapidly reproduced to form plasma cells.

D. The second exposure was more infectious.

Markscheme

C

Examiners report

This question proved to be the hardest on the paper, with fewer candidates answering correctly than the ‘guess’ level of 25 %. The low discrimination index showed that even well-prepared candidates struggled. Most candidates thought that antibodies could be stored in the body. Although antibodies do persist for a time after an infection, the question referred to a second infection ‘later in life’, implying too long a delay for antibodies to persist. Guidance in sub-topic 6.3 states that students are expected to know that memory cells persist after an infection and can quickly reproduce to form a clone of plasma cells that produce antibodies. The expected answer to the question was therefore that lymphocytes can rapidly reproduce to form plasma cells. Perhaps candidates did not appreciate that memory cells are lymphocytes.

Syllabus sections

Core » Topic 6: Human physiology » 6.3 Defence against infectious disease
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