2.6.A—Explain how the structure of a molecule affects its ability to pass through the plasma membrane

Explain how the structure of a molecule affects its ability to pass through the plasma membrane.

• Facilitated diffusion requires transport or channel proteins to enable the movement of charged ions across the membrane.
  • i. Membranes may become polarized by the movement of ions across the membrane.
  • ii. Charged ions, including Na+ (sodium) and K+ (potassium), require channel proteins to move through the membrane.
• Facilitated diffusion enables the movement of large polar molecules through membranes with no energy input. In this type of diffusion, substances move down the concentration gradient.
• Aquaporins transport large quantities of water across membranes.