HIV is a communicable disease caused by a virus. Explain how the human body responds to HIV once it has entered the bloodstream, including the roles of lymphocytes, phagocytes and memory cells.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
White blood cells recognise HIV in the blood by receptors that bind to viral antigens.
Lymphocytes then produce antibodies that are complementary to those antigens, binding and neutralising the virus.
The antibodies can also agglutinate HIV particles, making them easier targets for phagocytes.
Phagocytes engulf the antibody‑coated virus and digest it with enzymes (phagocytosis).
After the infection, memory cells persist, so if HIV is encountered again the immune response is faster and antibodies are produced more quickly.
Lymphocytes then produce antibodies that are complementary to those antigens, binding and neutralising the virus.
The antibodies can also agglutinate HIV particles, making them easier targets for phagocytes.
Phagocytes engulf the antibody‑coated virus and digest it with enzymes (phagocytosis).
After the infection, memory cells persist, so if HIV is encountered again the immune response is faster and antibodies are produced more quickly.
Examiner tips
- Use the exact terms: receptors, antigens, antibodies, agglutination, phagocytosis, memory cells.
- Show the sequence: detection → antibody production → agglutination → phagocytosis → memory.
- Keep each point concise to cover all five marks.
Common mistakes
- Confusing lymphocytes with phagocytes; they are different cell types.
- Omitting the role of memory cells or describing them as ‘long‑lasting’ without linking to faster response.
Mark scheme (5 marks)
- White blood cells detect the HIV virus using receptors on their cell surface to identify antigens on the pathogen
- Lymphocytes release antibodies that are specific / complementary to the antigens on HIV, which bind to the antigens to neutralise the virus
- Lymphocytes activate phagocytes / antibodies clump HIV particles together (agglutination) making them easier for phagocytes to destroy
- Phagocytes engulf / ingest HIV particles and digest them using enzymes (phagocytosis)
- Memory cells remain after the infection so that if HIV is encountered again, the immune response is faster / antibodies are produced more quickly
Key terms in this question
communicable disease · lymphocyte · phagocyte · memory cell
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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