Unicellularity

Unicellularity refers to organisms made up of just one cell, which performs all necessary life functions independently. Unlike multicellular organisms, like humans or trees, these single-celled organisms—such as bacteria, protozoa, and certain algae—carry out processes like growth, reproduction, and response to the environment within a single cell. Despite their simplicity, unicellular organisms can be incredibly diverse, adaptable, and vital to ecosystems, playing roles like decomposing material, producing oxygen, or causing illnesses. Their ability to function autonomously in a single cell distinguishes them as the most basic form of life on Earth.