Final answer:
The channels and pumps in the phospholipid bilayer are formed by proteins, with integral proteins acting as the main components for transport functions in the cell membrane.
Step-by-step explanation:
The channels and pumps in the phospholipid bilayer of cell membranes are primarily formed by proteins. These proteins are crucial for the transportation of molecules across the cell membrane. Specifically, integral proteins act as channels or pumps that facilitate the movement of substances in and out of the cell.
While phospholipids form the foundational structure of the bilayer, providing a barrier that separates the interior of the cell from its external environment, carbohydrates are typically involved in cell-cell adhesion and serve as recognition sites on the cell's surface.
Moreover, cholesterol molecules within the bilayer contribute to the membrane's fluidity and flexibility, ensuring that the membrane maintains its integrity under various physical stresses. Meanwhile, proteins can be categorized as integral or peripheral, based on their position and function in the membrane.