Biology

The correct answer is: A.Proteins.

Explanation:

In the phospholipid bilayer of the cell membrane, proteins form the channels and pumps that are crucial for transporting molecules across the membrane. These proteins are embedded in the bilayer and perform various functions, including:

1.Channel proteins: These proteins form pores or channels in the membrane that allow specific molecules or ions to pass through, usually through passive transport (e.g., facilitated diffusion).

2.Carrier proteins (pumps): These proteins actively transport molecules against their concentration gradient using energy (often from ATP). This process is known as active transport.