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.