What are the basic units of living things referred to?

Cells are considered the fundamental units of living things because they are the smallest structures capable of performing all life processes. Every living organism, from the simplest bacteria to complex multicellular organisms like plants and animals, is composed of one or more cells. Cells carry out essential functions such as metabolism, energy production, growth, and reproduction. They also contain genetic material that helps in the transfer of hereditary information.

In contrast, organs, tissues, and systems are hierarchical structures built from cells. Tissues are groups of similar cells that perform a specific function, organs are composed of multiple tissue types working together, and systems are collections of organs that collaborate to carry out complex functions. Thus, while these terms describe larger organizational structures in biological systems, cells are uniquely distinguished as the basic operational units of life.