Cells perform numerous tasks at the same time throughout their life, and many of these functions depend on the external environment of not only the cell but also the organism. However, many times, different cells need to perform different tasks at the same time and communication is necessary. Cells can signal each other using certain molecules, and they can decipher these messages through receptors on the plasma membrane and some second messenger molecules present in cells. Cell communication is crucial to the survival of an organism. In fact, if a cell receives no signals, it signals apoptosis. The three steps to cell signaling are reception, transduction, and response. In reception, a cell signaling molecule binds to a receptor protein on the cell membrane or inside the cell if the signaling molecule is hydrophobic and can pass through the membrane. In transduction, the binding of the molecule to the receptor induces a conformational change, and the signal is converted into a form to which the cell can respond. Usually, this requires a sequence of changes within the cell, and this is called a signal transduction pathway. The final stage is the response, and this can manifest in countless ways. It could be anything from the catalysis by an enzyme to the rearrangement of the cytoskeleton to reproduction.