Floating microscopic heterotrophs are mostly grouped as

Step 1: Analyze the question The question asks for the group of organisms that are (a) floating, (b) microscopic, and (c) heterotrophic, meaning they cannot make their own food.

Step 2: Explain the concepts Plankton are organisms that drift in water and cannot swim strongly against currents. They fall into two main groups:

• Phytoplankton are plant-like and contain chlorophyll. They are autotrophs that photosynthesize (e.g. diatoms, algae).
• Zooplankton are animal-like. They are heterotrophs that feed on phytoplankton or other organisms (e.g. copepods, protozoans, larvae of small animals).

Other terms in the options:

• Microbes is a general term for all microscopic organisms (bacteria, some fungi, protozoa). It does not specifically mean floating heterotrophs in water.
• Nekton are active swimmers, such as fish, which are not microscopic.

Step 3: Apply to the options

• A. Phytoplankton: floating and microscopic, but autotrophic. ❌
• B. Zooplankton: floating, microscopic and heterotrophic. ✅
• C. Microbes: too broad, and not specific to floating heterotrophs. ❌
• D. Nekton: they swim actively and are large. ❌

Step 4: Answer The correct option is B. zooplankton.

Exam tip: Remember the Greek roots. Phyto means plant, so phytoplankton make their own food. Zoo means animal, so zooplankton eat other organisms. Also remember that nekton swim, plankton drift.