AP BIOLOGY

Detailed explanation-1: -Transduction is the second step of cell signaling and involves the binding of signaling molecules to the receptor which in turn initiates a series of events in the transduction pathway.

Detailed explanation-2: -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-3: -Sodium does not serve as the secondary messenger for any hormone.