Which term describes an organism that is composed of only one cell?

The term that describes an organism composed of only one cell is "unicellular." These organisms consist of a single cell that performs all the necessary functions required for life, such as metabolism, growth, reproduction, and response to the environment. Common examples of unicellular organisms include bacteria, archaea, and many protists.

Multicellular organisms, in contrast, are composed of multiple cells that work together to carry out the functions of life. This organization allows for cellular specialization, where different cells take on specific roles within the organism.

Prokaryotic refers to a type of cell that does not have a nucleus or membrane-bound organelles and includes all unicellular organisms classified as bacteria and archaea. While all prokaryotes are unicellular, not all unicellular organisms are prokaryotic, as some unicellular organisms, like certain protists, are eukaryotic.

Eukaryotic pertains to cells that have a nucleus and membrane-bound organelles, which includes both unicellular and multicellular organisms such as plants, animals, fungi, and some protists.

Thus, the correct answer, "unicellular," accurately identifies organisms made up of a single cell.