Foundation definition in Protozoology: How is a protozoan best defined for introductory classification purposes?

Introduction:
Protozoa are traditionally taught as the animal-like protists. The purpose of this item is to check the learner’s ability to recall the baseline definition that separates protozoa from prokaryotes, fungi, plants, and multicellular animals.

Given Data / Assumptions:

• We are working with classic textbook terminology used in medical and general microbiology.
• “Protozoan” refers to a single cell that is eukaryotic and typically motile.
• Modern systematics may reclassify groups, but the teaching definition remains consistent.

Concept / Approach:
Key keys: eukaryotic cell organization (true nucleus, membrane-bound organelles), unicellular body plan, and typical motility (flagella, cilia, or pseudopodia). Nutrition is generally holozoic or mixotrophic rather than strictly photosynthetic like algae. Therefore, the concise definition is “motile eukaryotic unicellular protist.”

Step-by-Step Solution:
Identify the domain level: protozoa are eukaryotes, not prokaryotes. Identify the body plan: unicellular rather than multicellular. Identify typical behavior: locomotion via flagella, cilia, or pseudopodia. Exclude obligate photosynthetic criteria that fit algae rather than classic protozoa.

Verification / Alternative check:
Representative genera (Amoeba, Paramecium, Giardia, Trichomonas) all exhibit eukaryotic cellular architecture and are single-celled with characteristic motility. None are prokaryotic or obligatorily multicellular.

Why Other Options Are Wrong:
Motile prokaryotic unicellular protist – protozoa are not prokaryotes.

Motile eukaryotic unicellular photosynthetic protist – describes many algal cells, not classic protozoa.

Motile eukaryotic multicellular protist – protozoa are single-celled.

Non-motile eukaryotic multicellular alga – not protozoa by definition.

Common Pitfalls:
Assuming “protist” means prokaryote; prokaryotes are bacteria/archaea. Also, thinking photosynthesis is mandatory; most protozoa are not primarily photosynthetic.

Final Answer:
Motile eukaryotic unicellular protist.