Cholera is a communicable disease caused by the bacterium Vibrio cholerae. Explain how cholera spreads between individuals and describe TWO ways in which the body defends itself against pathogens such as Vibrio cholerae.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cholera causes severe diarrhoea and dehydration. Outbreaks are common in areas where clean drinking water is not available.
Model answer (5 marks)
Cholera is a water‑borne disease; it spreads when people drink or eat food that has been contaminated with the bacterium Vibrio cholerae.
The bacterium enters the body by ingestion of contaminated water or food.
The first line of defence is a physical/chemical barrier – for example, the acidic environment of the stomach (hydrochloric acid) kills many bacteria, and mucus in the gut traps pathogens.
A second defence is the adaptive immune response: B‑lymphocytes recognise the specific antigens on V. cholerae and produce antibodies. These antibodies bind the bacteria, neutralise them and mark them for destruction by other immune cells.
The bacterium enters the body by ingestion of contaminated water or food.
The first line of defence is a physical/chemical barrier – for example, the acidic environment of the stomach (hydrochloric acid) kills many bacteria, and mucus in the gut traps pathogens.
A second defence is the adaptive immune response: B‑lymphocytes recognise the specific antigens on V. cholerae and produce antibodies. These antibodies bind the bacteria, neutralise them and mark them for destruction by other immune cells.
Examiner tips
- Mention water‑borne transmission and ingestion; name stomach acid and mucus as barriers; state B‑cell antibody production and its effect; keep answer concise and use exam terminology.
Common mistakes
- Confusing inhalation with ingestion as the route of entry; omitting the specific role of antibodies; using vague terms like "immune system" without specifying B‑cells or antibodies.
Mark scheme (5 marks)
- Cholera is a water-borne disease, spread through contaminated water (or food)
- The bacterium enters the body when contaminated water or food is consumed / ingested
- First named physical / chemical barrier defence — e.g. hydrochloric acid in the stomach kills bacteria / mucus traps pathogens / cilia waft pathogens away from the lungs
- B-lymphocytes produce antibodies specific to the antigen on Vibrio cholerae
- Antibodies trigger an immune response that destroys / neutralises the pathogen (or leads to its destruction)
Key terms in this question
communicable disease · pathogen
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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