What type of protein forms a pore across the cell membrane allowing specific ions to diffuse?

The type of protein that forms a pore across the cell membrane, allowing specific ions to diffuse, is an ion channel. Ion channels are integral membrane proteins that provide a passageway for ions to move in and out of cells. This movement is crucial for various cellular processes, including generating action potentials in neurons and regulating cellular homeostasis.

Ion channels are highly selective, meaning they are designed to allow only certain types of ions to pass through based on size, charge, or other properties. This selectivity ensures that the proper ion concentrations are maintained within the cell compared to the external environment.

In contrast, receptor proteins are involved in signal transduction by binding to specific molecules and triggering responses within the cell. Carrier proteins, on the other hand, facilitate the transport of substances across the membrane but do so by changing shape rather than forming an open pore. Transport proteins is a broader category that can include both carrier proteins and ion channels, but it does not specifically refer to the pore-forming proteins responsible for ion diffusion. Thus, the correct identification of ion channels highlights their unique role in the selective passage of ions across the cell membrane.