What is the term for a living thing that can function independently?

An organism is defined as any individual living entity that can perform all the necessary life processes independently. This includes being able to grow, reproduce, respond to stimuli, and maintain homeostasis. Organisms can be unicellular, such as bacteria, or multicellular, like plants and animals.

The other terms do not fit this definition as they refer to specific components or classifications within biology. A cell is the basic unit of life, but it cannot function independently if it is part of a multicellular organism. An organ is a collection of tissues that work together to perform specific functions, and it relies on other organs for the complete functioning of an organism. A species is a group of similar organisms that can breed and produce fertile offspring, but it does not refer to the individual capability of functioning independently. Therefore, to encapsulate the essence of a living thing that operates on its own, the term 'organism' is the most appropriate choice.