Cellular Transport Mechanism

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Cellular Transport Mechanism 1. Diffusion - movement of molecules from an area of greater concentration to an area of lesser concentration; occurs because molecules have free energy. They are constantly in motion. Oxygen and Carbon dioxide are exchanged by diffusion in the lungs. 2. Osmosis - the diffusion of water. Water diffuses to an area of less water, that is, to an area of more dissolved material. The Small Intestines absorbs water from digested food by osmosis. 3. Facilitated diffusion - carrier enzymes that are part of the cell membrane permit cells to take in materials that would not diffuse in by them selves. Most cells take in glucose by facilitated diffusion. 4. Active transport - a cell uses ATP to move substances from an area of lesser concentration to an area of greater concentration. Nerve cells and muscle cells have sodium pumps to return Na+ ions to the exterior of the cells; this prevents spontaneous impulses. Cells of the small intestines absorb glucose and amino acids from digested food by active transport. 5. Filtration - pressure forces water and dissolved materials through a membrane from an area of higher pressure to an area of lower pressure. Tissue fluid is formed by filtration: Blood pressure forces plasma and dissolved nutrients out of the capillaries and into tissue. Blood pressure in the kidney capillaries creates filtration that is the first step in the formation of urine. 6. Phagocytosis - a moving cell that engulfs something; white blood cells phagocytize bacteria to destroy them. 7. Pinocytosis - a stationary cell engulfs small molecules; kidney tubule cells reabsorb small proteins by

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