AP BIOLOGY

Detailed explanation-1: -There are four basic categories of chemical signaling found in multicellular organisms: paracrine signaling, autocrine signaling, endocrine signaling, and signaling by direct contact.

Detailed explanation-2: -In multicellular organisms, growth factors, hormones, neurotransmitters, and extracellular matrix components are some of the many types of chemical signals cells use.

Detailed explanation-3: -Chemical signals between cells are called ligands. A ligand is a molecule that binds another specific molecule. In the case of cell signaling, the ligand binds a receptor, a protein in or on the target cell. Examples of ligands include hormones and neurotransmitters.

Detailed explanation-4: -The neurotransmitters are transported across the very small distances between nerve cells, which are called chemical synapses. The small distance between nerve cells allows the signal to travel quickly; this enables an immediate response.