What is a fundamental postulate of cell theory?

The statement that cells are the smallest units of life captures a core principle of cell theory, which fundamentally asserts that all living organisms are composed of one or more cells and that these cells function as the basic building blocks of all life processes. This means that regardless of size or complexity, any living entity ultimately relies on cells to carry out all biological functions, such as metabolism, growth, and reproduction. This principle distinguishes living organisms from non-living matter.

In contrast, the other statements do not align with the established principles of cell theory. The idea that all living things can survive without cells contradicts the very definition of life, as cells are essential for sustaining life. The assertion that all cells have a nucleus is also incorrect, as prokaryotic cells, like bacteria, do not possess a nucleus. Lastly, the claim that only certain organisms are made of cells overlooks the fact that every living organism, from single-celled bacteria to complex multicellular organisms, is made up of cells. Thus, the correct assertion revolves around the critical role of cells as the smallest units of life within all living organisms.