Which statement best describes pore transport across membranes?

Which statement best describes pore transport across membranes?

• A. Water cannot cross the membrane
• B. Ions diffuse freely without transport proteins
• C. Large proteins cross via pores
• D. Small molecules cross lipid membrane rapidly through nanometer pores

Answer: (D)

Pore transport across membranes relies on protein channels that form aqueous pores, providing a low-energy pathway for small solutes to diffuse down their concentration gradient. Because these channels create a hydrated route through the hydrophobic lipid core, small molecules and ions can pass quickly, which is why statements describing rapid diffusion through nanometer-scale pores best capture how this route works. Water and ions don’t diffuse freely across the membrane without help—water can cross faster through channels like aquaporins, and ions require specific channels or transporters due to their charge and hydration shell. Large proteins are far too big for such pores to accommodate, so they don’t use pore transport.

Pore transport across membranes relies on protein channels that form aqueous pores, providing a low-energy pathway for small solutes to diffuse down their concentration gradient. Because these channels create a hydrated route through the hydrophobic lipid core, small molecules and ions can pass quickly, which is why statements describing rapid diffusion through nanometer-scale pores best capture how this route works. Water and ions don’t diffuse freely across the membrane without help—water can cross faster through channels like aquaporins, and ions require specific channels or transporters due to their charge and hydration shell. Large proteins are far too big for such pores to accommodate, so they don’t use pore transport.