AP BIOLOGY

Detailed explanation-1: -In order to detect a signal (that is, to be a target cell), a neighbor cell must have the right receptor for that signal. When a signaling molecule binds to its receptor, it alters the shape or activity of the receptor, triggering a change inside of the cell.

Detailed explanation-2: -A target cell responds to a hormone because it bears receptors for the hormone. In other words, a particular cell is a target cell for a hormone if it contains functional receptors for that hormone, and cells which do not have such a receptor cannot be influenced directly by that hormone.

Detailed explanation-3: -Signal transduction pathways start with signal recognition. Here, the signals in the environment are perceived by proteins on the cell surface, called receptors. The specific receptors a cell has determines which signals it can detect and thus respond to.

Detailed explanation-4: -What determines how a cell responds to such a hormone? A cell is able to respond to a hormone only if it has a receptor protein on the cell surface or inside the cell that can bind to the hormone.

Detailed explanation-5: -They are found in the cytoplasm of a cell and are often targeted by hydrophobic ligands that can cross the lipid bilayer of the animal plasma cell membrane. Often these receptors act to modify mRNA synthesis and thus protein synthesis within the cell.