Final answer:
The dispatch of a message from outside of a cell to its interior typically involves a signaling molecule binding with a membrane receptor protein. Option (A)
Step-by-step explanation:
For a message to be sent from outside of a cell to the inside, several mechanisms may be utilized, depending on the nature of the signaling molecule. Cell signaling pathways often begin with the binding of a signaling molecule, or ligand, to a membrane receptor protein. This interaction is highly specific, and the initiation of this pathway is known as reception. Polar signaling molecules, like hormones or neurotransmitters, cannot diffuse through the lipid bilayer of the cell membrane and thus typically interact with membrane receptor proteins. These receptors may change shape to allow ions to pass through the membrane or may initiate a cascade of intracellular events involving G-proteins or secondary messengers.
Some small nonpolar molecules, such as O2 or CO2, can diffuse across the cell membrane without assistance due to their solubility properties. However, this is not the usual method for signal transmission, which often requires the intermediary role of membrane proteins including carrier proteins and channel proteins.
Therefore, the correct answer to the student's question is:
A. A signaling molecule binds with a membrane protein.