ap bio chap 7 osmosis and diffusion. so, how does a membrane regulates what goes in and out? depends...
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![Page 1: AP Bio Chap 7 Osmosis and Diffusion. So, how does a membrane regulates what goes in and out? Depends on: 1)Lipid solubility - Hydrophobic molecules, such](https://reader030.vdocument.in/reader030/viewer/2022032722/56649cea5503460f949b4dd5/html5/thumbnails/1.jpg)
AP Bio Chap 7Osmosis and Diffusion
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So, how does a membrane regulates what goes in and out?
Depends on:1) Lipid solubility - Hydrophobic molecules, such as hydrocarbons, O2, CO2
pass freely - Ions, polar molecules need transport molecules (proteins)
with hydrophilic channels or actually bind to the carrier protein to pass through
- Aquaporins facilitate water passage2) Size of the molecule3) Concentration of the molecule
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Cell membranes are semipermeable.
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Types of transport: PASSIVE TRANSPORT – no energy required
1) Diffusion - movement of a substance from greater to lesser concentration (down its concentration gradient)
• will continue until dynamic equilibrium; no more NET movement
• most common method of movement for nonpolar molecules across the membrane
• most efficient when large surface area, well-defined concentration gradient, short distance.
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Diffusion
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Molecules of dye
Fig. 7-11a
Membrane (cross section)
WATER
Net diffusion Net diffusion
(a) Diffusion of one solute
Equilibrium
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(b) Diffusion of two solutes
Fig. 7-11b
Net diffusion
Net diffusion
Net diffusion
Net diffusion
Equilibrium
Equilibrium
The diffusion of one solute is unaffected by the diffusion of another solute.
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2) Osmosis is the diffusion of water across a selectively permeable membrane
• Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration
• Direction of water flow is determined by the number (not kinds) of solute particles (molecules and ions)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Lowerconcentrationof solute (sugar)
Fig. 7-12
H2O
Higher concentrationof sugar
Selectivelypermeablemembrane
Same concentrationof sugar
Osmosis
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Fig. 7-UN3
Environment:0.01 M sucrose
0.01 M glucose
0.01 M fructose
“Cell”
0.03 M sucrose
0.02 M glucose
What will happen here if the sucrose cannot diffuse? Glucose, fructose, and water can.
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Fig. 7-UN4
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Water Balance of Cells Without Walls
• Tonicity is the ability of a solution to cause a cell to gain or lose water
• Isotonic solution: Solute concentration is the same as that inside the cell; no NET water movement across the plasma membrane
• Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water
• Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water
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REMEMBER!
WATER ALWAYS FLOWS INTO A HYPERTONIC SITUATION!
WATER ALWAYS FLOWS INTO A HYPERTONIC SITUATION!
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What happens to animal cells in the following situations?
• Hypertonic environment – lose water, shrivel• Hypotonic environment – water moves in, cell
swell and possibly bust• Adaptations to contend with this: - contractile vacuoles in protists - membranes less permeable to water - isotonic internal conditions to their
environment
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Fig. 7-13
Hypotonic solution
(a) Animal cell
(b) Plant cell
H2O
Lysed
H2O
Turgid (normal)
H2O
H2O
H2O
H2O
Normal
Isotonic solution
Flaccid
H2O
H2O
Shriveled
Plasmolyzed
Hypertonic solution
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Fig. 7-14
Filling vacuole 50 µm
(a) A contractile vacuole fills with fluid that enters from a system of canals radiating throughout the cytoplasm.
Contracting vacuole
(b) When full, the vacuole and canals contract, expelling fluid from the cell.
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Water Balance of Cells with Walls
• Cell walls help maintain water balance• A plant cell in a hypotonic solution swells until the wall
opposes uptake; the cell is now turgid (firm)• If a plant cell and its surroundings are isotonic, there is no
net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt
• In a hypertonic environment, plant cells lose water; eventually, the membrane pulls away from the wall, a usually lethal effect called plasmolysis
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???• The ideal environment for animal cells is
________________________.• The ideal environment for plant cells is
________________________.
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• Hypertonic or hypotonic environments create osmotic problems for organisms
• Osmoregulation, the control of water balance, is a necessary adaptation for life in such environments
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