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

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

Answer: (B)

Motile, unicellular organisms with a nucleus belong to the group known as protozoans. Protozoans are eukaryotes that live as single cells, and many of them move by beating cilia—tiny hairlike structures that propel the cell through water. This combination of having a true nucleus and using cilia for movement helps distinguish protozoans from bacteria, which lack a nucleus and typically don’t have cilia for locomotion, and from algae or fungi, which have other defining features such as photosynthesis in many algae or non-motile, often multicellular forms in fungi.