1. Facilitated Diffusion: This process uses carrier proteins to move molecules across the cell membrane down their concentration gradient (from high to low concentration). This means it doesn't require energy. Examples include the transport of glucose into cells.
2. Active Transport: This process uses carrier proteins to move molecules across the cell membrane against their concentration gradient (from low to high concentration). This requires energy, usually supplied by ATP. Examples include the sodium-potassium pump, which maintains the concentration gradient of these ions across the cell membrane.
Both facilitated diffusion and active transport rely on specific carrier proteins that bind to the molecule being transported. This binding changes the shape of the protein, allowing the molecule to pass through the membrane.
