An example of a parasitic protozoan is

1. Analyze the question We need the option that is both a protozoan (a single-celled, animal-like organism) and a parasite (it lives on or in a host and harms it).

2. Explain the concept Protozoans are grouped by how they live and move:

• Free-living protozoans feed on their own in water, e.g. Paramecium and Amoeba.
• Parasitic protozoans live inside a host, e.g. Plasmodium, Trypanosoma, Entamoeba histolytica and Giardia.

3. Go through each option

• A. Paramecium is a free-living, ciliated protozoan found in ponds. It is not a parasite.
• B. Plasmodium is the protozoan that causes malaria. It lives in human red blood cells and liver cells, and the female Anopheles mosquito carries it as a vector. It is a parasite.
• C. Euglena (spelled "Eughlena" in the question) is a free-living, flagellated organism. It has chloroplasts, so it can photosynthesize, and it is not parasitic.
• D. Chlamydomonas is a green alga. It is free-living and photosynthetic, and it is not a protozoan at all.

4. Answer Only Plasmodium is a parasitic protozoan, so the correct option is B.

5. Exam tip Link the name to the disease: Plasmodium → malaria, Trypanosoma → sleeping sickness, Entamoeba → amoebic dysentery. If you see one of these names in a "parasitic protozoan" question, pick it. Remember that Paramecium, Euglena and Chlamydomonas are all free-living.