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Cell Processes Review. Selective Permeability. Cell membranes are selectively permeable (for homeostasis). Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all.
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Selective Permeability • Cell membranes are selectively permeable (for homeostasis). Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all. • Materials move into and out of cells through either passive transport or active transport.
Passive Transport • Passive Transport - movement of molecules from a more crowded area to a less crowded area WITHOUT the use of energy. • Movement occurs when there are unequal concentrations of a substance inside and outside of the cell.
Passive Transport • SOME SUBSTANCES SUCH AS WATER, OXYGEN, AND CARBON DIOXIDE, CAN CROSS THE CELL MEMBRANE WITHOUT ANY INPUT OF ENERGY BY THE CELL.
Passive Transport • Diffusion - movement of molecules from a region of higher concentration to a region of lower concentration. • Osmosis - diffusion of water through a membrane. • Facilitated Diffusion: special carrier protein molecules within the cell membrane act as shuttle buses to transport a molecule into/out of a cell.
Active Transport • ActiveTransport - movement of molecules from a less crowded to a more crowded area WITH the use of energy. • UNLIKE PASSIVE TRANSPORT, ACTIVE TRANSPORT REQUIRES A CELL TO EXPEND OR USE ENERGY. THERE ARE THREE TYPES OF ACTIVE TRANSPORT: CELL MEMBRANE PUMPS, ENDOCYTOSIS, AND EXOCYTOSIS.
ENDOCYTOSIS • DURING ENDOCYTOSIS, THE CELL MEMBRANE FOLDS IN AND FORMS A SMALL POUCH. • THE POUCH THEN PINCHES OFF FROM THE CELL MEMBRANE TO BECOME A VESICLE.
EXOCYTOSIS • DURING EXOCYTOSIS, A VESICLE MOVES TO THE CELL MEMBRANE, FUSES WITH IT, AND THEN RELEASES IT CONTENTS TO THE OUTSIDE OF THE CELL.
ACTIVE TRANSPORT • SODIUM POTASSIUM PUMP ACTIVELY PUMPS SODIUM OUT OF THE CELL AND ACTIVELY PUMPS POTASSIUM INTO THE CELL, CREATING AN ELECTRICAL GRADIENT ACROSS THE CELL MEMBRANE.
