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Cell Structure 4A - Membranes
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unit membrane a thin structure composed of proteins and lipids
type of membrane found around all cells around many of the structures inside cells the outer boundary of a cell
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Important Property of Membranes
selectively permeable: certain molecules go through them and other molecules do not
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Selectively Permeable
Not all membranes are permeable to the same molecules. However water, oxygen, and carbon dioxide are small and easily passes through most membranes.
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How does a substance pass through a unit membrane?
Passive Transport Active Transport
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PASSIVE TRANSPORT the passage of substances across a membrane without the use of energy This is the main way.
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two main forms of passive transport
Diffusion Osmosis
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diffusion the movement of molecules from an area of higher concentration to an area of lower concentration
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diffusion diffusion can be speeded up by such things as heat,movement, and pressure
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the diffusion of water through a membrane
osmosis the diffusion of water through a membrane
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ACTIVE TRANSPORT the passage of particles through a membrane; requires the use of cellular energy (sometimes because of the size of the molecule being so large, or going against gradient)
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