Organisms are living lifeform that inhabit Earth. The term applies from larger animals such as the vertebrates, insects, plants, and bacterium.

An organism may be either unicellular (a single cell) or, as in the case of humans, comprise many trillions of cells grouped into specialized tissues and organs. The term multicellular (many cells) describes any organism made up of more than one cell.

Anatomy of an amiotic egg This article is part of Project Glossary, a All Birds project that aims to write comprehensive articles on each term related to animals.

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