Which of the following is an example of a microorganism in action as a disease vector?

Step 1: Analyze the question The question asks for an example of a disease vector in action. A vector is an organism that carries and transmits a pathogen from one host to another, usually without being killed by the disease itself.

Step 2: Explain the concept

• Pathogen: the organism that causes the disease (e.g. Plasmodium, bacteria, viruses).
• Vector: the carrier that transmits the pathogen (e.g. female Anopheles mosquito, housefly, tsetse fly, tick).
• Vectors can be biological (the pathogen develops or multiplies inside them, as with Plasmodium in the mosquito) or mechanical (they simply carry the pathogen on their bodies, as with houseflies carrying cholera or typhoid germs).

Step 3: Evaluate each option

• A. Fungi decomposing dead plant material: this is decomposition and nutrient recycling. There is no disease transmission.
• B. Mosquito transmitting malaria: the female Anopheles mosquito carries Plasmodium and passes it to humans when it bites. This is a classic vector example.
• C. Bacteria causing food poisoning: here the bacteria are the pathogen causing disease directly, not a vector carrying it.
• D. Algae producing oxygen: this is photosynthesis, which is unrelated to disease.

Step 4: A note on wording Strictly speaking, a mosquito is an insect (an arthropod), not a microorganism. The question's wording is loose. The microorganism in the malaria example is Plasmodium, the parasite the mosquito transmits. Still, option B is the only one that describes vector-borne disease transmission, so it is clearly the intended answer.

Answer: B. Mosquito transmitting malaria

Tip: Remember the pair "pathogen = causes disease, vector = carries it." In JAMB, whenever you see "vector," think of mosquito (malaria, yellow fever), housefly (cholera, typhoid), tsetse fly (sleeping sickness), and tick or louse. Also watch for loosely worded questions: choose the option that best fits the key concept being tested.