What role do transport proteins play in the process of facilitated diffusion across a cell membrane?

• A. They create a concentration gradient for molecules to diffuse.
• B. They increase the energy required for molecules to diffuse.
• C. They actively transport molecules against their concentration gradient.
• D. They provide a pathway for molecules to move down their concentration gradient.

Answer: (D)

Verified step by step guidance

1. Facilitated diffusion is a type of passive transport that allows molecules to move across the cell membrane without the use of cellular energy (ATP).
2. Transport proteins are integral membrane proteins that provide a pathway for specific molecules to pass through the cell membrane.
3. These proteins assist in the movement of molecules down their concentration gradient, meaning from an area of higher concentration to an area of lower concentration.
4. There are two main types of transport proteins involved in facilitated diffusion: channel proteins and carrier proteins.
5. Channel proteins form pores in the membrane, allowing specific molecules or ions to pass through, while carrier proteins undergo a change in shape to transport the molecule across the membrane.