Which statement about facilitated diffusion is true?

Which statement about facilitated diffusion is true?

• A. Requires energy
• B. Uses carrier proteins
• C. Moves against gradient
• D. Occurs only in mitochondria

Answer: (B)

Facilitated diffusion is a passive transport process that uses membrane proteins to help substances cross the lipid bilayer down their concentration gradient. It does not require cellular energy. The proteins involved are carrier proteins (which bind and shuttle solutes) or channel proteins (which form pores for ions and polar molecules). This is why using carrier proteins is the correct statement: these proteins enable diffusion of otherwise hard-to-pass substances without energy input. In contrast, moving against the gradient would need energy, and facilitated diffusion isn’t limited to mitochondria—it occurs across the plasma membrane and other membranes wherever the right transport proteins exist.

Facilitated diffusion is a passive transport process that uses membrane proteins to help substances cross the lipid bilayer down their concentration gradient. It does not require cellular energy. The proteins involved are carrier proteins (which bind and shuttle solutes) or channel proteins (which form pores for ions and polar molecules). This is why using carrier proteins is the correct statement: these proteins enable diffusion of otherwise hard-to-pass substances without energy input. In contrast, moving against the gradient would need energy, and facilitated diffusion isn’t limited to mitochondria—it occurs across the plasma membrane and other membranes wherever the right transport proteins exist.