Pretty sure its Ph scale i did a question like this once but i cant remember....its either Ph or richer
Answer:
Answer is D - cAMP.
Explanation:
cAMP is a small molecule that functions as an intracellular signaling molecule - a second messenger. The first messenger would be the thing that activated the GPCR (e.g. a hormone). The GPCR is a signal transducer (converts extracellular signal to intracellular signal). Once activated, the GPCR activates adenylate cyclase which can be called a signal effector - it is an enzyme that produces cAMP.