Hormone

A hormone is a substance produced by glands,cells or organs which transports a signal from one cell to another. They induce chemical changes at a cellular level and are necessary for development and growth along with many other features. Only small volumes of hormone are required to initiate a change in the cell's behaviour. Hormones are produced by all multicellular organisms, but are widely called phytohormones in plants. Examples of such phytohormones are auxins and ethylene

The word hormone derives from a Greek work meaning "to spur on".

Hormones can be categorised in many different ways, for example the way they reach the target cells (endocrine vs exocrine hormones), or the ways they interact with the target cell to induce a change (steroid vs peptide hormones).