DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ1.c

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Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ1.c
Level SL Paper 2 Time zone TZ1
Command term Explain Question number c Adapted from N/A
c.
[Maximum mark: 7]
22M.2.SL.TZ1.c

Explain how cells and cell components in the blood defend the body against infectious disease.

[7]

Markscheme

Platelets: [3 max]

  1. damage/cuts to blood vessels causes platelets to be activated;
  2. the platelets release clotting factors;
  3. initiates cascade of reactions
    OR
    fibrinogen is converted to fibrin;
  4. forms a mesh over the damaged area;
  5. prevents pathogens from entering the body;

    Phagocytes: [3 max]
  6. phagocytes/phagocytic white blood cells in the blood travel to the site of infection;
  7. (phagocytes) squeeze between the capillary cells;
  8. (phagocytes) engulf/ingest/take in pathogens;
  9. the pathogen is digested/broken down by/within the phagocyte;

    Lymphocytes: [3 max]
  10. lymphocytes recognize a particular fragment/antigen of a pathogen;
  11. (lymphocytes) release antibodies;
  12. (antibodies) provide specific immunity;
  13. memory cells provide rapid response giving long-term immunity (to pathogens previously recognized);
  14. antibodies destroy pathogens;

ECF may be applied when candidates use white blood cells in place of specific terms.

Examiners report

Among all candidates, there was knowledge of how each of the blood components (platelets, phagocytes, lymphocytes) can defend against infectious disease; each of the marking points in the mark scheme was eventually awarded; popular ideas were that fibrin is formed, phagocytes engulf pathogens and antibodies provide specific immunity.

Correct terminology was confused or was not employed in too many answers.

Syllabus sections