Which Molecules Need Facilitated Diffusion to Move Across the Plasma Membrane?

Facilitated diffusion is a process that allows specific molecules to cross the plasma membrane with the help of transport proteins. Molecules that typically require facilitated diffusion include:

• Glucose: Due to its size and polarity, glucose cannot easily pass through the lipid bilayer without assistance. Specialized proteins called glucose transporters help transport glucose into the cell.
• Amino Acids: Like glucose, amino acids are relatively large and polar, which makes direct passage through the membrane difficult. Transport proteins facilitate their movement into cells where they are needed for protein synthesis and other metabolic processes.
• Ions: Charged particles such as sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and chloride (Cl^–) cannot freely cross the hydrophobic lipid bilayer. Ion channels or carrier proteins assist in their transport across the membrane, allowing for important physiological functions like nerve impulse transmission.

Overall, facilitated diffusion is crucial for transporting these molecules across the plasma membrane, ensuring that the cell maintains homeostasis and can carry out its functions effectively.