Organs

An organ is a grouping of similar tissues. It is a higher categorical level denoting the structure of cells in a biological organism. Examples of organs include the stomach, heart, liver, and brain.

Due to its foundational composition of cells, all organs are made from fully living components.

A grouping of organs with similar function is termed an organ system. All organ systems are contained within organisms, but not all organisms have organ systems, or they only have a few: all prokaryotes, as well as the eukaryotic sponges and fungi, lack organ systems entirely, and plants only have two organ systems. As shown, an organism does not require organ systems to be defined as an organism. An organism also does not require organs to be defined as an organism, but any entity that possesses organs and/or an organ system is defined as an organism.