Malaria is a communicable disease caused by a protist spread through the bite of a female mosquito. Describe how the human body responds to the Plasmodium protist after it has entered the bloodstream, including the roles of phagocytes and lymphocytes.

WJEC A-Level Biology (Wales) — 3.2 Respiration · Describe · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Malaria is caused by the protist Plasmodium falciparum, which is transmitted to humans via the bite of a female mosquito. Once inside the body, the protist enters the bloodstream where the immune system responds to destroy it.

Model answer (5 marks)

White blood cells recognise the Plasmodium protist via receptors that bind to its surface antigens.
Phagocytes, such as macrophages, then engulf the protist and digest it with enzymes in phagosomes (phagocytosis).
Lymphocytes, particularly B‑cells, are activated and release antibodies that are complementary to the protist’s antigens.
These antibodies bind to the protist, neutralising it and causing agglutination, which makes it easier for phagocytes to destroy it.
After the infection, memory B‑cells remain, allowing a faster and stronger response if the same protist re‑enters the bloodstream.

Examiner tips

  • Use the exact terms: phagocytes, lymphocytes, antibodies, memory cells. Show the sequence: detection → phagocytosis → antibody production → agglutination → memory. Keep each point short and to the point to hit all 5 marks.

Common mistakes

  • Mixing up phagocytes with lymphocytes or vice‑versa. Failing to mention the role of antibodies or memory cells. Using vague language such as "immune system" without specifying cell types.

Mark scheme (5 marks)

  1. White blood cells detect the protist using receptors on their cell surface that identify antigens on the surface of the pathogen
  2. Phagocytes engulf / ingest the protist into the cell and digest it using enzymes (phagocytosis)
  3. Lymphocytes release / trigger the release of antibodies that are specific / complementary to the antigens on the protist
  4. Antibodies bind to the antigens on the protist to neutralise it / clump the cells together (agglutination) making it easier for the immune system to destroy it
  5. Memory cells remain after the infection so that if the same pathogen enters the body again, it can be destroyed more quickly

Key terms in this question

phagocyte · lymphocyte

Related

More Respiration questions

▶ Try answering this question with AI marking (free) →