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Published byRosamund Philippa Gallagher Modified over 5 years ago
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Substances cross the cell membrane without the cell expending energy
Passive Transport Substances cross the cell membrane without the cell expending energy
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Simple Diffusion Substances spread out by moving from areas of high concentration to areas of lower concentration Moves “downhill”
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Facilitated Diffusion
Substances diffuse across the cell membrane through special channels in proteins Proteins are specific (fit a certain substance)
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Osmosis The diffusion of molecules through a selectively permeable membrane Water moves “down” the concentration gradient – from an area of high water concentration to an area of lower water concentration
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The force exerted by osmosis
Osmotic Pressure The force exerted by osmosis Due to water moving from a more dilute solution into a more concentrated solution (ex: water moving from an area of very little salt to an area with a lot of salt)
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Remember, water can easily pass through the cell membrane
This can cause problems for a cell
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To Control Osmotic Pressure
Bacteria & plants use a cell wall – prevents cell from expanding too much Pump out water using the contractile vacuole Bathe cells in blood – cells do not come in direct contact with water (in our bodies)
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The concentration of water is equal inside and outside the cell
Isotonic Solution The concentration of water is equal inside and outside the cell “equilibrium” – no net movement of water Water molecules are still moving!
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There is a higher concentration of water outside the cell
Hypotonic Solution There is a higher concentration of water outside the cell More water moves in than out The cell expands (explodes)
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There is a higher concentration of water inside the cell
Hypertonic Solution There is a higher concentration of water inside the cell More water moves out than in The cell shrinks
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Substances use energy to cross the cell membrane
Active Transport Substances use energy to cross the cell membrane Substances move AGAINST the concentration gradient (upstream) as they move from areas of LOW concentration to areas of HIGH concentration
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Methods of Active Transport
Membrane proteins can act as PUMPS
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Endocytosis vs. Exocytosis
Can take in large molecules 3. Exocytosis The opposite of endocytosis
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