cell transport ch. 7.3 & 7.4
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Cell Transport
Ch. 7.3 & 7.4
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Plasma Membrane
Membrane Lipids• Cell
membranes consist of a phospholipid bilayer
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Plasma Membrane
Membrane Proteins• Cell membranes often contain proteins
embedded within the phospholipid bilayer.
3
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Plasma Membrane
Fluid Mosaic Model• the phospholipid bilayer behaves like a
fluid more than it behaves like a solid.
4
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Diffusion
• Diffusion– the movement of a substance from an area of high
concentration to an area of lower concentration – caused by the random motion of particles of the
substance
Chapter 4
5
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passive transport– movement across the cell membrane that does not
require energy
• concentration gradient– A difference in the concentration of a substance, across
a space
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Equilibriumequilibrium
the concentration of a substance is equal throughout a
space
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Some substances move across the cell membrane
without any use of energy by the cell.
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Simple Passive Diffusion
• Many substances enter or leave cells by diffusing across the cell membrane.
10
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Osmosis• osmosis
– the diffusion of water through a selectively permeable membrane
– determined by solute concentration on both sides of the cell
Chapter 4
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Osmosis is a type of passive transport
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There are three possibilities for the direction of water movement:
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Osmosis
Hypertonic solution– solute concentration
outside the cell is HIGHER THAN the cytosol
– there is a NET movement of water out of the cell.
– the cell shrinks.
Chapter 4
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OsmosisHypotonic solution
– solute concentration outside the cell is LOWER THAN the cytosol
– there is a NET movement of water into the cell.
– the cell swells.
15
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Isotonic solution
– the solute concentration outside the cell is EQUAL TO the cytosol
– there is no NET movement of water.
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Osmosis
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Compare
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Facilitated Diffusion
• Passive transport across the membrane using an embedded protein
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Carrier proteins
bind to a specific substance on one side of the cell membrane,
carry the substance across the cell membrane, and release it on
the other side.
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• Ion channel
–a transport protein with a polar pore through which ions can pass.
20
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Movement Against a Concentration Gradient
• active transport– the transport of a substance across the cell
membrane against its concentration gradient. Energy is required.
21
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Comparing Active and Passive Transport
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Movement in Vesicles
• endocytosis – The movement of larger substances across the cell
membrane by vesicles.
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exocytosis
the movement of a substance by a vesicle to the
outside of a cell
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