AP BIOLOGY

Detailed explanation-1: -Often, cells that are near one another communicate through the release of chemical messengers (ligands that can diffuse through the space between the cells). This type of signaling, in which cells communicate over relatively short distances, is known as paracrine signaling.

Detailed explanation-2: -For instance, neurotransmitters are a class of short-range signaling molecules that travel across the tiny spaces between adjacent neurons or between neurons and muscle cells.

Detailed explanation-3: -Depending on the ligand’s origin (from the same cell, from the neighbour cell or from far distance), recptor-ligand interaction and signaling pathway activation is classified into four different types: autocrine, endocrine, paracrine and juxtacrine.

Detailed explanation-4: -Direct signaling (also called juxtacrine signaling) involves communication between cells that are in direct contact with each other. This communication is often mediated by gap junctions in animal cells and plasmodesmata in plant cells. Autocrine singaling occurs when a ligand acts on the same cell that releases it.

Detailed explanation-5: -1: Synapsis: The distance between the presynaptic cell and the postsynaptic cell-called the synaptic gap-is very small and allows for rapid diffusion of the neurotransmitter.