Associate Safety Professional Practice Exam

Which organisms are classified as single-celled parasitic organisms?

1. Bacteria

2. Protozoa

3. Viruses

4. Fungi

The correct answer is: Protozoa

Protozoa are classified as single-celled parasitic organisms because they are eukaryotic microorganisms that can exist as free-living entities in various environments or as parasites within a host organism. As parasites, protozoa can live in the body of a host, obtaining nutrients at the host’s expense, which may lead to disease. Common examples include species that cause malaria (Plasmodium) and amoebic dysentery (Entamoeba histolytica). Their ability to adapt to different environments and their complexity relative to other categories of microorganisms reinforce their classification as single-celled parasites. Bacteria, while often single-celled, are prokaryotic organisms and can be either beneficial or harmful, but they are not classified as parasitic in the same sense as protozoa. Viruses, on the other hand, are not considered living organisms as they cannot replicate independently and lack cellular structure. Fungi are primarily multicellular organisms (with the exception of yeast) and are not classified as parasites in the same way as protozoa; instead, they usually decompose organic matter or form mutualistic relationships rather than living strictly as parasites.