Which type of membrane protein assists in moving substances across a cell membrane?

Transport proteins are crucial for moving substances across a cell membrane. This category includes both channel and carrier proteins, which facilitate the passage of ions and molecules that cannot freely cross the lipid bilayer due to their size, polarity, or charge.

Channel proteins create specific pathways through the membrane that allow certain ions or water to flow through by diffusion, while carrier proteins change shape to carry substances across the membrane. Therefore, the term "transport proteins" broadly encompasses both types, making it the most accurate choice to describe proteins involved in facilitating the movement of substances across cellular membranes.

Other types of membrane proteins, such as peripheral proteins, do not assist in transport. Instead, they typically serve structural roles or are involved in signaling pathways.