What is required for facilitated diffusion to occur?

Facilitated diffusion relies on specific transport proteins to assist the movement of molecules across the cell membrane. This process is essential when substances cannot easily pass through the lipid bilayer due to their size, polarity, or charge. The transport proteins—such as channel proteins and carrier proteins—provide a pathway that allows these molecules to move along their concentration gradient, meaning from an area of higher concentration to an area of lower concentration without requiring energy.

The presence of these specific transport proteins is crucial because they ensure that only certain molecules can be selectively transported, thereby maintaining the cell's internal environment. This selective permeability is vital for cellular function and homeostasis.

The other options, while they may relate to cellular transport processes, do not accurately describe the requirements for facilitated diffusion. Energy from ATP is involved in active transport, not facilitated diffusion, which is a passive process. Cell membrane channels alone may not suffice if there are no specific proteins present that facilitate the transport of particular molecules. Additionally, low temperature conditions are not a prerequisite for this process; facilitated diffusion can occur at various temperatures as long as the necessary transport proteins are available.