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AS · Practice questions · Pathogens and how they are transmitted

Name the pathogen, then trace its route.

Six original Cambridge-style questions on infectious diseases, from naming the four species of Plasmodium to explaining why TB spreads in crowded housing.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Disease, pathogen, type, route.

01
Recall
[2 marks]

State what is meant by an infectious disease.

  • A disease caused by a pathogen (a microorganism or virus). ✓
  • That is transmissible: it can be passed from one person (host) to another. ✓
02
Recall
[4 marks]

Complete the statement: malaria is caused by four species of a pathogen. Name the four species and state the type of organism they are.

  • Plasmodium falciparum and Plasmodium malariae. ✓
  • Plasmodium ovale and Plasmodium vivax. ✓
  • They are protoctists. ✓
  • (single-celled eukaryotes; accept protoctists / protists, not bacteria) ✓
03
Explain
[4 marks]

Explain how malaria is transmitted from one person to another.

  • A female Anopheles mosquito acts as the vector. ✓
  • It takes a blood meal from an infected person and takes in Plasmodium gametes. ✓
  • The parasite develops inside the mosquito and moves to its salivary glands. ✓
  • When the mosquito bites another person it injects saliva containing the parasite into the blood. (also: blood transfusion, shared needles, across the placenta) ✓
04
Explain
[4 marks]

Explain why tuberculosis spreads most rapidly among people living in crowded, poorly ventilated housing.

  • TB bacteria are released in droplets when an infected person coughs or sneezes. ✓
  • In a crowded room people are close together, so more people breathe in the droplets. ✓
  • Poor ventilation means the droplets stay in the air for longer and are not diluted. ✓
  • Poverty linked to crowding may mean poor diet or HIV infection, so immune systems are weaker. ✓
05
Analysis
[3 marks]

Compare the transmission of cholera with the transmission of HIV.

  • Cholera is transmitted by the faecal-oral route, in water or food contaminated with faeces; HIV is transmitted in body fluids. ✓
  • Cholera bacteria enter by being swallowed; HIV enters the blood (through sex, needles, transfusion, or from mother to baby). ✓
  • Neither has a vector; cholera bacteria can survive in water outside the body, but HIV does not survive long outside the body. ✓
06
Data
[3 marks]

In a village, cases of TB rose among farm workers who drank milk straight from their own cattle, even though none lived in crowded housing. Suggest which pathogen was most likely involved, how it was transmitted and one measure to prevent further cases.

  • Mycobacterium bovis. ✓
  • It was transmitted from infected cattle in unpasteurised milk. ✓
  • Pasteurise (heat-treat) milk before drinking; or test cattle and remove infected animals. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.