A

David

Darling

organ

An organ is a collection of tissues that performs a particular function or set of functions in an animal or plant's body. The heart, brain, and skin are three organs found in most animals. The leaf, stem, and root are three organs found in most plants. Organs are composed of tissues, and may be organized into larger organ systems. Organs, such as the vermiform appendix in humans, are termed vestigial organs.