What are the two main types of protein channels involved in transport across the cell membrane?

The correct answer identifies the two main types of protein channels as carrier proteins and channel proteins, which play integral roles in the movement of substances across the cell membrane.

Carrier proteins function by binding to specific molecules and changing shape to transport these substances across the membrane. This process can occur in both passive and active transport, where passive transport does not require energy, while active transport does, utilizing ATP to move substances against their concentration gradient.

Channel proteins, on the other hand, create passages or pores that allow specific ions or molecules to passively move across the membrane. These channels can also be gated, meaning they can open and close in response to signals, further regulating the movement of molecules based on the cell’s needs.

Understanding these two types of proteins is crucial in cell biology, as they facilitate essential functions like nutrient absorption and maintaining cellular homeostasis. While the other options refer to different transport mechanisms or classifications, they do not specifically relate to the main types of protein channels required for transport across the cell membrane.