Which of the following organisms are primarily made up of one cell?

Bacteria are primarily made up of one cell, categorizing them as unicellular organisms. They consist of a single cell that carries out all the necessary life processes, including metabolism, reproduction, and response to the environment. This single-cell structure allows them to survive in a variety of environments and adapt quickly to changes.

In contrast, plants, animals, and fungi are made up of multiple cells (multicellular organisms). These organisms have specialized cells that perform specific functions, allowing for more complex structures and systems. While some fungi can be unicellular (like yeast), the majority are multicellular. Hence, bacteria are the most representative of organisms that are solely one cell, distinct in their simplicity and efficiency as unicellular life forms.