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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.

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slide2

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

slide3

What is Osmosis ?

  • 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.

Important points

slide4

Lower concentration of solute (sugar)

Higher concentration of solute (sugar)

Same concentration of sugar

Selectively permeablemembrane

Water molecules can pass through pores, but sugar cannot

Water molecules cluster around sugar molecule

Fewer solute molecules, more free water molecules

More solute molecule, fewer free water molecules

types isotonic
Types: Isotonic

isotonic solution: a solution that has the same salt concentration as the normal cells of the body and the blood.

  • 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.

Plant cell

types isotonic cont inued
Types: Isotonic (continued)
  • “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)

Osmotic pressure on blood cell diagram.

types hypotonic
Types: Hypotonic

hypotonic solution: the solution that has higher water potential than the other solution.

  • 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.

Plant cell

types hypotonic continued
Types: Hypotonic (continued)
  • When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode

Osmotic pressure on

blood cell diagram.

types hypertonic
Types: Hypertonic

hypertonic solution: the solution that has the lower water potential than the other solution.

  • 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.

Plant cell

types hypertonic continued
Types: Hypertonic (continued)
  • 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.

Osmotic pressure on

blood cell diagram.

slide12

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.

More important key terms

lab demo
Lab Demo.

enjoy this…

slide19

Try it !

Yourself

the movement of water
The Movement of Water

Purpose:

To study the movement of water across a membrane

Materials:

3 rectangular pieces of potato

3 beakers (250mL)

Centigram balance

2 salt solutions

Distilled water

Paper towel

the movement of water1
The Movement of Water

Procedure:

Record the masses of all potatoes pieces. Note all physical characteristics.

Label 3 beakers as ‘5% salt solution’, ‘0.9% salt solution’ or ‘distilled water’ using a marker and labeling tape.

Place potato piece in each of the beakers

In beaker 1 pour enough 5% salt solution to cover the potato

In beaker 2 pour enough 0.9% salt solution to cover the potato

In beaker 3 pour enough distilled water to cover the potato

Allow the samples to sit overnight (or two)

The next day remove the potatoes from the solutions and blot to dry using paper towel

Observe any changes in physical appearance and mass the samples again.