In which of the following habitats is Paramecium no found

Analyze the question: The question asks where Paramecium is not found. (The question says "no found", which means "not found".)

Concept: Paramecium is a freshwater, single-celled protozoan (a ciliate). It lives in still or slow-moving freshwater that is rich in decaying organic matter and bacteria, which it feeds on. Typical habitats include:

• Ponds
• Puddles and ditches
• Stagnant pools
• Slow streams
• Lakes (especially the shallow edges with vegetation)

Working through the options:

• A. Pond: Yes. This is the classic habitat, with still water and plenty of organic matter.
• B. Aquarium: An aquarium is usually a managed freshwater setting. Paramecium can appear in it, especially if there is decaying matter, but it is not a natural habitat. The question is asking which option is not a natural habitat.
• C. Lake: Paramecium is found here, particularly in shallow, vegetated areas.
• D. Puddle: Paramecium is found here too, in temporary freshwater with decaying matter.

Ponds, lakes and puddles are natural freshwater habitats where Paramecium is commonly found. An aquarium is an artificial, human-made environment, so it is the odd one out. Be aware that Paramecium can sometimes turn up in aquaria, so the question is a bit loosely worded. Even so, B is the intended answer.

Answer: B. Aquarium

Exam tip: For "habitat" questions about Paramecium, think "natural stagnant freshwater with decaying organic matter": ponds, puddles, ditches and lakes. When one option is artificial or man-made, it is often the intended exception.