DP Biology (first assessment 2025)

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Question 20N.2.SL.TZ0.6c

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Date November 2020 Marks available [Maximum mark: 7] Reference code 20N.2.SL.TZ0.6c
Level SL Paper 2 Time zone TZ0
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 7]
20N.2.SL.TZ0.6c
(c)

Explain the role of cells in the defence against infectious disease.

[7]

Markscheme

a. cells of skin provide a physical barrier/produce fatty acids/lactic acid/lysozyme which stops entry of microbes
OR
mucous membranes produce mucus to trap pathogens
OR
stomach cells produce hydrochloric acid which kills microbes;

b. platelets start the clotting process preventing access of pathogens;

c. (two types of) white blood cells fight infections in the body;

d. phagocytes ingest pathogens (by endocytosis/phagocytosis);

e. gives non-specific immunity to diseases / ingest any type of pathogen;

f. production of antibodies by lymphocytes/B cells;

g. in response to particular pathogens/antigens;

h. gives specific immunity;

i. lymphocyte/B cell makes only one type of antibody;

j. plasma cells produce large quantity of (one type of) antibody;

k. some lymphocytes act/remain as memory cells;

l. can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered;

m. results in faster defence against second exposure to specific antigen/pathogen/disease;

Examiners report

In part (c), defence against infection was well known. Poor candidates lost marks by using loose, non-biological expressions such as the ‘white blood cells eat the infection/disease’. However, most had a fair idea of the cellular response to infection.

Syllabus sections