Which of the following organisms is a protozoan?

Plasmodium is classified as a protozoan because it belongs to the kingdom Protista and is characterized by its single-celled structure and eukaryotic cell type. Protozoans are typically simple, unicellular microorganisms that can be found in various environments, often exhibiting locomotion through structures such as cilia, flagella, or pseudopodia. Plasmodium species, specifically, are known for causing malaria, a significant parasitic disease transmitted through the bites of infected Anopheles mosquitoes.

In contrast, yeast is a type of fungus, multicellular bacteria comprise organisms like E. coli, and Staphylococcus refers to a genus of bacteria. All of these are fundamentally distinct from protozoans, as they do not share the same characteristics or classification under the kingdom Protista.