Explain why communicable diseases can spread rapidly through a population.

AQA GCSE Biology (8461) — 4.3.1 Communicable diseases · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Communicable diseases are caused by pathogens such as bacteria, viruses, fungi or protists. These pathogens can be transferred from an infected person to another person by person‑to‑person transmission. They can spread through several routes – direct contact, contaminated water or food, airborne droplets or via vectors such as mosquitoes. Once a new host is infected the pathogen can reproduce rapidly, producing more infectious units and thereby increasing the number of infected individuals.

Examiner tips

Use the exact terminology – pathogen, person‑to‑person transmission, routes of spread, rapid reproduction.
Show the chain: pathogen → transmission route → new host → rapid multiplication → more cases.
Keep the answer concise and structured to hit all four points.

Common mistakes

Using vague terms like "diseases" instead of "pathogens".
Omitting one of the transmission routes or the rapid reproduction step.
Writing a long paragraph that repeats the same idea without covering all points.

Mark scheme (4 marks)

Communicable diseases are caused by pathogens (e.g. bacteria, viruses, fungi, protists)
Pathogens can be transferred from one infected person to another (person-to-person transmission)
Pathogens can be spread by multiple routes, e.g. direct contact, contaminated water/food, air/droplets, vectors
Once inside a new host, pathogens can reproduce rapidly, increasing the number of infected individuals

Key terms in this question

communicable disease