HIV is a communicable disease that can lead to AIDS. Explain how HIV affects the immune system and why people with AIDS are more likely to die from other infections.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
HIV is transmitted through bodily fluids and destroys white blood cells. Over time, this leads to AIDS, in which the immune system is severely weakened.
Model answer (5 marks)
HIV attacks and destroys CD4+ T‑cells, a type of white blood cell that coordinates immune responses.
1. Loss of CD4+ cells reduces the number of lymphocytes and phagocytes available.
2. Fewer lymphocytes mean fewer antibodies are produced and fewer phagocytes can engulf pathogens.
3. The immune system becomes weakened and cannot respond effectively to new infections.
4. Pathogens that enter the body are not neutralised or destroyed quickly.
5. Consequently, other infections can take hold and become fatal because the body cannot mount an adequate specific defence.
1. Loss of CD4+ cells reduces the number of lymphocytes and phagocytes available.
2. Fewer lymphocytes mean fewer antibodies are produced and fewer phagocytes can engulf pathogens.
3. The immune system becomes weakened and cannot respond effectively to new infections.
4. Pathogens that enter the body are not neutralised or destroyed quickly.
5. Consequently, other infections can take hold and become fatal because the body cannot mount an adequate specific defence.
Examiner tips
- Use the term CD4+ T‑cells and link to antibody production and phagocytosis; show the chain from cell loss to weakened immunity; mention ‘specific defence’ to hit the last point.
- Structure answer in five clear points to match the 5 marks.
Mark scheme (5 marks)
- HIV destroys / attacks white blood cells
- Fewer lymphocytes / phagocytes available to produce antibodies or carry out phagocytosis
- The immune system is weakened / cannot respond effectively to pathogens
- Pathogens that enter the body cannot be neutralised / destroyed as quickly or effectively
- Other infections / diseases can therefore take hold and become fatal because the immune system cannot mount an adequate specific defence
Key terms in this question
HIV · AIDS · immune system
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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