In biology, cell signaling (cell signalling in British English) or cell communication is the ability of cells to receive, process, and transmit signals with its environment and with itself. It is a fundamental property of all cells in every living organism such as bacteria, plants, and animals. Signals that originate from outside a cell (or extracellular signals) can be physical agents like mechanical pressure, voltage, temperature, light, or chemical signals (e.g., small molecules, peptides, or gas). Chemical signals can be hydrophobic or hydrophillic. Cell signaling can occur over short or long distances, and as a result can be classified as autocrine, juxtacrine, intracrine, paracrine, or endocrine. Signaling molecules can be synthesized from various biosynthetic pathways and released