Biology

The correct answer is: D.Secondary messengers.

Explanation:

cAMP (cyclic adenosine monophosphate) and calcium ions (Ca²⁺) are examples of secondary messengers. These molecules are involved in intracellular signaling pathways that are activated by the binding of a primary messenger (like a ligand or hormone) to a cell surface receptor. Once the primary messenger activates the receptor, secondary messengers like cAMP or calcium help relay the signal inside the cell and amplify the response.

Here’s why the other options are incorrect:

A.Hormones: Hormones are signaling molecules that are released by...