CholeraSpec 10.1.16, 10.1.17
In short
Cholera is a disease caused by a bacterium transmitted in contaminated water. The bacterium produces a toxin in the small intestine that makes the cells lining it secrete chloride ions. This lowers the water potential in the gut, so water moves in from the blood by osmosis, causing diarrhoea, dehydration and loss of ions from the blood.
Cholera is a disease caused by a bacterium. It is transmitted in contaminated water, so it spreads where drinking water is not clean or sewage is not treated.
The cholera bacterium lives in the small intestine and produces a toxin. The toxin has these effects:
- The toxin causes cells lining the small intestine to secrete chloride ions into the small intestine.
- The chloride ions lower the water potential in the gut, so water moves into the gut from the blood by osmosis.
- The extra water causes diarrhoea.
- Large amounts of water and ions are lost from the body, so the person becomes dehydrated and loses ions from the blood.
(opens full size in a new tab)Put the sequence in order: toxin, chloride ions secreted, water moves in by osmosis, diarrhoea. Name osmosis.
Quick check
What is a pathogen?
Show answer
A disease-causing organism.
What is a transmissible disease?
Show answer
A disease in which the pathogen can be passed from one host to another.
Name the body defences in the syllabus.
Show answer
Skin, hairs in the nose, mucus, stomach acid and white blood cells.
Supplement Which route of transmission is cholera associated with?
Show answer
Contaminated water.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026