A single-celled organism is commonly referred to as a unicellular organism.
Unicellular organisms are the simplest forms of life, consisting of just one cell that performs all the necessary functions to sustain life. These organisms can be found in various environments, from soil and water to living inside other organisms. Examples include bacteria, protozoa, and some algae.
The term ‘unicellular’ highlights their unique nature; unlike multicellular organisms, which consist of many cells that differentiate and work together to perform complex functions, unicellular organisms rely on their single cell to carry out all biological processes. These can include metabolism, reproduction, and responsiveness to environmental stimuli.