Monday, June 9, 2008

Passive and Active Transport

Passive and active transport are the two main means of transport in a cell. Passive transport requires no energy. Some examples of passive energy are diffusion, facilitated diffusion, and osmosis. In diffusion, liquids, gases, and solids can move in and out of a cell without energy. In facilitated diffusion, diffusion is occurred but with some type of carrier. Osmosis is diffusion for water. Passive transport always involves the movement of molecules from high concentration to low concentration. Active transport, on the other hand, always involves the movement of molecules from low concentration to high concentration. It requires energy in the form of ATP. Some examples of active transport are ion pumps, exocytosis, and endocytosis. Ion pumps are proteins that gather ions on one side of the membrane. In exocytosis, a vesicle holding material can break off the membrane and leave the cell. In endocytosis, a cell ingests a substance into the cell which then forms a vacuole.

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