A pore in a cell membrane through which ions can pass is called an

• A. Carrier protein
• B. Ion pump
• C. Ion channel
• D. Channel receptor

Answer: (C)

An ion channel is a membrane protein that forms a pore through which ions can flow. This pore allows ions to move passively down their electrochemical gradient, often very rapidly, and the channel can be gated to open or close in response to signals. This contrasts with carrier proteins, which bind ions and undergo conformational changes to shuttle them across without forming a continuous pore. Ion pumps actively move ions against their gradient using energy, so they’re about active transport rather than creating a simple pore. Channel receptors describe channels that also function as receptors, but the term ion channel most directly captures the idea of a pore that ions pass through.