Passive Transport:
* Diffusion: Movement of molecules from an area of high concentration to low concentration, driven by the concentration gradient. Examples: Oxygen, carbon dioxide.
* Facilitated Diffusion: Movement of molecules across a membrane with the help of a membrane protein, still following the concentration gradient. Examples: Glucose, amino acids.
* Osmosis: Movement of water across a selectively permeable membrane from an area of high water concentration to low water concentration.
Active Transport:
* Primary Active Transport: Requires energy directly from ATP to move molecules against their concentration gradient. Examples: Sodium-potassium pump.
* Secondary Active Transport: Uses the energy stored in the concentration gradient of one molecule to move another molecule against its gradient. Examples: Glucose transport coupled to sodium gradient.
Other Mechanisms:
* Bulk Transport:
* Endocytosis: Taking in large molecules or particles by engulfing them in a membrane-bound vesicle. Examples: Phagocytosis, pinocytosis.
* Exocytosis: Releasing substances from the cell by fusing a vesicle with the cell membrane.
The specific mechanisms used by a cell depend on the size and type of substance being transported, the concentration gradient, and the cell's energy requirements.
