Unicellular organisms that have a nucleus and can swim with the aid of cilia are examples of which group?

• A. Monerans.
• B. Plants.
• C. Fungi.
• D. Protozoans.

Answer: (D)

Unicellular eukaryotes that swim with the aid of cilia are protozoans. The key idea is that these organisms have a true nucleus, setting them apart from bacteria (monerans), which lack a nucleus and are prokaryotic. Cilia are short, hair-like structures that beat to propel the cell, a common motion strategy in many protozoans such as ciliates like Paramecium. Plants and fungi, in contrast, are typically multicellular and have different lifestyles and structures (photosynthesis in plants; absorptive nutrition and chitin-containing cell walls in fungi), so they don’t fit the description of a unicellular, nucleus-containing organism that uses cilia for movement. Protozoans encompass these motile, single-celled eukaryotes, making them the best fit for the scenario.