Differential or selective permeability valuable cell proteins and other substances are kept within the cell and excreta or wastes pass to the exterior Active processes the cell provides ATP to power the transport Passive processes the transport process is driven by concentration or pressure differences between the interior and exterior of the cell Two Passive Processes 1 Diffusion movement of molecules from a region of higher concentration to a region of lower concentration Diffusions driving force is the kinetic E of molecules a Simple diffusion when a solute dissolved in water moves thru a selectively permeable membrane b Osmosis movement of water thru a selectively permeable membrane 2 Filtration process by which water and solutes pass thru a membrane from an area of higher hydrostatic fluid pressure into an area of lower hydrostatic pressure ex fluids and solutes filter out of the capillaries in the kidneys into the kidney tubules bc blood pressure in the capillaries is greater than the fluid pressure in the tubules Active Transport when a cell expends cellular energy ATP to move substances across its membrane may be too large to pass thru the membrane channels may not be lipid soluble or may have to move agst rather than with a concentration gradient Substances move across the membrane by combining with a carrier protein molecule Pinocytosis cell membrane sinks beneath the material to form a small vesicle which then pinches off into the cell interior Most common for taking in liquids containing protein or fat Phagocytosis cell eating parts of the plasma membrane and cytoplasm expand and flow around a relatively large or solid material such as bacteria or cell debris and engulf it forming a membranous sac called a phagosome It is then fused with a lysosome and its contents are digested
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