What type of organism is made up of a single cell?

The organism made up of a single cell is classified as unicellular. This term specifically refers to organisms consisting of only one cell, which carries out all the functions necessary for life. Unicellular organisms can be found in various groups including bacteria, protozoa, and some algae.

While options such as prokaryotic and eukaryotic refer to cellular structure and complexity, they do not exclusively denote single-celled organisms. Prokaryotic organisms, like bacteria, are typically unicellular, but not all unicellular organisms are prokaryotic as some, like certain protozoa and yeast, are eukaryotic. On the other hand, multicellular organisms consist of multiple cells and are not relevant to the question of single-celled organisms.

By focusing on the definition and characteristics of unicellular organisms, it is clear that this answer directly addresses the query about organisms composed of a single cell.