Here's a breakdown:
* Diffusion: The movement of molecules from an area of high concentration to an area of low concentration. This is a passive process driven by the concentration gradient.
* Facilitated diffusion: A type of passive transport where a membrane protein helps the movement of a molecule across the cell membrane, still following the concentration gradient. This is needed for molecules that can't easily pass through the lipid bilayer on their own.
* Ion channels: Proteins that act as pores or channels in the cell membrane, allowing specific ions to pass through. They are often gated, meaning they can be opened or closed depending on cellular signals.
Key features of facilitated diffusion:
* Passive: No additional energy is required from the cell.
* Downhill: Movement occurs from high to low concentration.
* Specific: Each protein facilitates the transport of a specific molecule or ion.
Example:
Sodium ions (Na+) are transported into a cell through sodium channels by facilitated diffusion, following the concentration gradient. This movement does not require the cell to expend energy.
Contrast with active transport:
Active transport requires energy from the cell to move molecules against their concentration gradient, moving them from low to high concentration.
