Passive Transport:
* Diffusion: Movement of molecules from an area of high concentration to an area of low concentration. This doesn't require energy from the cell.
* Simple diffusion: Molecules move directly across the membrane, like oxygen and carbon dioxide.
* Facilitated diffusion: Molecules move across the membrane with the help of transport proteins. This is for larger or charged molecules that can't easily pass through the membrane on their own, like glucose.
* Osmosis: The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration. This is important for maintaining cell volume and pressure.
Active Transport:
* Requires energy (usually from ATP) to move molecules against their concentration gradient (from low concentration to high concentration). This is important for moving essential nutrients into the cell and removing waste products.
* Types of active transport:
* Protein pumps: Transport proteins use energy to move specific molecules across the membrane.
* Endocytosis: The cell engulfs large molecules or particles by wrapping its membrane around them, forming a vesicle.
* Exocytosis: Vesicles inside the cell fuse with the cell membrane and release their contents outside the cell.
Here's a breakdown of how different substances are transported:
* Nutrients:
* Glucose: Facilitated diffusion and active transport (sodium-glucose cotransporter).
* Amino acids: Active transport.
* Fatty acids: Simple diffusion (small fatty acids) and facilitated diffusion (larger fatty acids).
* Water: Osmosis.
* Wastes:
* Carbon dioxide: Simple diffusion.
* Nitrogenous waste: Active transport.
* Other waste products: Exocytosis.
Overall, cell membrane transport is a complex process that allows cells to maintain their internal environment, acquire essential nutrients, and eliminate waste products. This is crucial for the cell's survival and function.
