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

• A. Protozoans
• B. Bacteria
• C. Algae
• D. Fungi

Answer: (A)

Unicellular organisms with a nucleus are eukaryotic protists, and those that swim using numerous short hair-like structures are ciliates. Ciliates are a group within protozoans, classic examples being Paramecium, which use cilia to swim and feed. The presence of a nucleus rules out bacteria, which are prokaryotic. While some algae are unicellular and have nuclei, many move by flagella or other means rather than cilia, and fungi are usually multicellular (with yeast as a unicellular exception that does not swim using cilia). So the description best fits protozoans.