Passive Transport (No Energy Required)
* Simple Diffusion: Movement of molecules from an area of high concentration to an area of low concentration. This is driven by the concentration gradient and requires no cellular energy. Examples include the movement of oxygen into cells and carbon dioxide out of cells.
* Facilitated Diffusion: Movement of molecules across a membrane with the help of transport proteins. This is still passive because it follows the concentration gradient, but it requires a specific protein to facilitate the movement. Examples include the transport of glucose into cells.
* Osmosis: Movement of water across a selectively permeable membrane from an area of high water concentration to an area of low water concentration. This is driven by the difference in water potential and requires no cellular energy.
Active Transport (Energy Required)
* Primary Active Transport: Movement of molecules against their concentration gradient using energy directly from ATP (adenosine triphosphate). This requires specialized protein pumps that use ATP hydrolysis to move molecules across the membrane. Examples include the sodium-potassium pump, which maintains the electrochemical gradient across cell membranes.
* Secondary Active Transport: Movement of molecules against their concentration gradient using the energy stored in the electrochemical gradient of another molecule. This is still active transport because it requires energy, but this energy comes from a pre-existing gradient established by primary active transport. Examples include the transport of glucose into intestinal cells.
Other Important Points:
* Bulk Transport: This involves the movement of large molecules or particles across the membrane. It requires energy and is further divided into:
* Endocytosis: The cell takes in large molecules or particles by engulfing them in a vesicle.
* Exocytosis: The cell releases large molecules or particles by fusing a vesicle containing the material with the cell membrane.
Let me know if you'd like more detail on any specific transport method!
