Question

arrow a is indicating a(n) ______ protein.
receptor
signal
transport
structural
enzyme

Explanation:

Receptor proteins bind to specific signaling molecules to initiate a cellular response. Signal proteins are the molecules that bind to receptors, transport proteins move substances across membranes, structural proteins provide support to cells and tissues, and enzymes catalyze biochemical reactions. Based on the context of the cell - membrane interaction shown in the image, if the arrow is pointing to a protein that binds to an external molecule to trigger a response inside the cell, it is likely a receptor protein.

Answer:

A. receptor