Active transport is a cellular process that involves the movement of molecules across a cell membrane against their concentration gradient, which means moving substances from a region of lower concentration to a region of higher concentration. This process requires energy, typically derived from ATP (adenosine triphosphate), because it goes against the natural diffusion tendency of substances.
In contrast to passive transport processes (like diffusion and facilitated diffusion), which do not require energy and occur along concentration gradients, active transport mechanisms use specific transport proteins or pumps embedded in the cell membrane to carry molecules across.
There are several types of active transport:
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Primary Active Transport: This directly uses energy from ATP to transport molecules. A common example is the sodium-potassium pump, which moves sodium ions out of a cell and potassium ions into the cell.
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Secondary Active Transport (Cotransport): This does not directly use ATP. Instead, it relies on the electrochemical gradient created by primary active transport. It can be further classified into symport (where both molecules move in the same direction) and antiport (where molecules move in opposite directions). An example is the sodium-glucose transport protein, which uses sodium ions moving down their gradient to help transport glucose into the cell against its gradient.
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Endocytosis and Exocytosis: These are specialized forms of active transport that involve the movement of larger molecules or particles.
- Endocytosis is the process by which cells internalize substances by engulfing them in vesicles formed from the cell membrane.
- Exocytosis is the process by which cells expel materials in vesicles that fuse with the cell membrane, releasing their contents outside the cell.
Overall, active transport is crucial for maintaining cellular homeostasis, regulating ion concentrations, and facilitating nutrient uptake and waste removal.
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