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Wednesday, March 9 th 2011. introducing Osmosis. What is Osmosis ?. Diffusion of a solvent (usually water molecules) through a semipermeable membrane from an area of low solute concentration to an area of high solute concentration. - PowerPoint PPT Presentation
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Wednesday, March 9th 2011
introducing
Osmosis
What is Osmosis ?
Diffusion of a solvent (usually water molecules) through a semipermeable membrane from an area of low solute concentration to an area of high solute concentration.
Net movement of water molecules through a semipermeable membrane from an area of higher water potential to an area of lower water potential.
Tendency of water to flow from a hypotonic solution (low concentration of dissolved substances) to hypertonic solution (higher concentration of dissolved substances) across a semipermeable membrane
Osmosis is the movement of water through a selectively permeable membrane
What is Osmosis ?
Important points
• It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane separating two solutions of differentconcentrations
• It is the diffusion on water (normally) through a semi-permeable membrane.
• It is from a dilute solution to a more concentrated solution.
Lower concentration of solute (sugar)
Higher concentration of solute (sugar)
Water molecules can pass through pores, but sugar cannot
Fewer solute molecules, more free water molecules
Selectively permeablemembrane
Same concentration of sugar
Water molecules cluster around sugar molecule
More solute molecule, fewer free water molecules
Effects of Osmosis on Water Balance
• No net movement between cell and environment. • Ex. When an animal or plant
cell is placed in a solution of sugar or salt in water, the medium isotonic (a solution with exactly the same water concentration as the cell) there will be no net movement across the membrane.
Types: Isotonic
Plant cell
isotonic solution: a solution that has the same salt concentration as the normal cells of the body and the blood.
• “iso” means the same
• Water flows across the membrane, but at the same rate in both directions.
• In an isotonic environment, the volume of an animal cell is stable.
• The concentration of solutes inside the cell are the same as inside the cell(equilibrium)
Types: Isotonic (continued)
Osmotic pressure on blood cell diagram.
• Cell gains water from the environment.
• The concentration of solutes inside the cell is higher than outside the cell.
• The concentration of water is lower than outside the cell.
Types: Hypotonic
hypotonic solution: the solution that has higher water potential than the other solution.
Plant cell
• When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode
Types: Hypotonic (continued)
Osmotic pressure on blood cell diagram.
• Cell loses water to environment.
• Water concentration inside the cell is higher than outside the cell.
• Solute concentration inside the cell is lower than outside the cell.
Types: Hypertonic
hypertonic solution: the solution that has the lower water potential than the other solution.
Plant cell
• When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel up in a plant cell and to die in an animal cell.
Types: Hypertonic (continued)
Osmotic pressure on blood cell diagram.
More important key terms
Osmoregulation: the control of water balance.
Plasmolysis: contraction of the protoplast of a plant cell as a result of loss of water from the cell.
enjoy this…
Lab Demo.
RESULTS
Solution Original Mass Final Mass Conclusion
5% Salt Solution 3.028 g 2.54 g Hypertonic Solution
0.9% Salt Solution
2.072g 2.241g Isotonic Solution
Distilled Water 2.332g 3.125 g Hypotonic Solution
Try it ! Yourself
The Movement of Water
Purpose: To study the movement of water across a membrane
Materials:3 rectangular pieces of potato 3 beakers (250mL)Centigram balance2 salt solutionsDistilled waterPaper towel
The Movement of Water
Procedure:1. Record the masses of all potatoes pieces. Note all physical characteristics. 2. Label 3 beakers as ‘5% salt solution’, ‘0.9% salt solution’ or ‘distilled water’ using
a marker and labeling tape.3. Place potato piece in each of the beakers 4. In beaker 1 pour enough 5% salt solution to cover the potato5. In beaker 2 pour enough 0.9% salt solution to cover the potato6. In beaker 3 pour enough distilled water to cover the potato7. Allow the samples to sit overnight (or two)8. The next day remove the potatoes from the solutions and blot to dry using paper
towel9. Observe any changes in physical appearance and mass the samples again.
Thank you for listening.
The
End.