AP BIOLOGY

Detailed explanation-1: -The initiation of a signaling pathway results in a cellular response to changes in the external environment. This response can take many different forms, including protein synthesis, a change in cell metabolism, cell division and growth, or even cell death.

Detailed explanation-2: -Answer and Explanation: Out of the molecules listed above, the one that is not involved in cell-to-cell signalling is option (d) cholesterol.

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.