This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cell Membrane and transpo protiens, Subject name: Physiology
One of the ways that cells communicate with each other is by secretion of various molecules. The secreted molecule is known as 
Select and explain. 
A. A receptor molecule, B. A signaling molecule., C. A spectrin tetramer, D. An integrin.
B: A signaling molecule.
Answer: B: A signaling molecule. 
Explanation: A signaling molecule is the way by which cells communicate with each other. Three general types of intercellular communication are mediated by messengers in the ECF: neural -in which neurotransmitters are released at synaptic junctions endocrine - in which hormones and growth factors reach cells the circulating blood or the lymph paracrine -in which the products of cells diffuse in the ECF to affect neighboring cells that may be some distance away.