1. 4.1 Cell Biology
Lesson 9

2. Learning objective:
All students: Produce a hypothesis based on prior knowledge of osmosis and plan a reliable investigation that can be used to test the effects of osmosis.

3. What is Osmosis?
The movement of water from high to low concentration through a partially permeable membrane
What is a partially permeable membrane
A membrane that has small holes in it & only lets small water molecules move through it. It does not let large solute molecules through.
What is the partially permeable membrane in the cell?
The cell membrane

4. New key terms! Isotonic solution –
the solution has the same solute concentration as the inside of the cell
Hypertonic solution –
the solution has a higher solute concentration than the inside of the cell
Hypotonic solution –
the solution has a lower solute concentration than the inside of the cell

5. Osmosis and Plant cells
Wilting plant upright plant
Osmosis and Plant cells
Flaccid – Plasmolysed!
Turgid
Wilting plant
Upright plant

6. Plasmolysis in onion cells

7. Turgid onion cells

8. Plant cells cell wall vacuole cytoplasm and cell membrane
A useful analogy is the bicycle tyre. The outer casing represents the cell wall; the inner tube represents the cytoplasm and the air inside represents the vacuole. When the tyre is pumped up, the air pressure pushes the inner tube against the outer casing. The outer casing cannot expand and so the pressure in the tube builds up until the tyre is firm
The cell absorbs water
by osmosis ....
....but the cell wall stops the
cell expanding any more

9. Animal cells don’t have a cell wall This means they either:
Swell and burst if water osmoses in
Shrink if too much leaves
Can no longer carry blood around body