1. Osmosis An Important Type of Diffusion
Definition:
The diffusion of water across a selectively permeable membrane from an area of HIGHER WATER CONCENTRATION to an area of lower water concentration.

2. Water…WOW! Water is vital to life
Plants and animals use water to carry out essential life processes
Water particles are small enough to travel across the cell membrane in both directions
If the water concentration is equal on both sides, the cell maintains its size.

3. What happens when there is an imbalance?
If there is more water either inside or outside the cell, the direction in which water moves across the cell membrane adjusts to this imbalance
More water will move in one direction than the other

4. Definition: SOLUTE
A substance that is dissolved in another substance – ie. Sugar and salt
Water moves by osmosis from an area with higher water (or lower solute) concentration to an area with lower water (or higher solute) concentration.
Osmosis continues until the concentration of water is equal on both sides of the membrane.
When concentrations are equal, osmosis ends and water continues to pass through the membrane in both directions at an equal rate.

5. Osmosis

6. Cells in Solution
Sugars, salts and proteins are common solutes in cells
Cells need to maintain solute concentrations at certain levels to stay alive and healthy
The movement of water into and out of the cell determines solute concentration

7. Environment A
Concentration of water molecules outside of the cell is EQUAL to concentration of water molecules inside the cell.
Movement of water is continuous
Shape and size of cell do not change
Environment B
Concentration of water molecules GREATER OUTSIDE than inside the cell.
More water molecules move INTO the cell than out
Cell INCREASES in size
If too much water enters the cell it may burst and die
Environment C
Concentration of water molecules GREATER INSIDE the cell than outside
More water molecules move OUT of the cell
Cell DECREASES in size
If too much water leaves the cell, it may die.

8. Turgor Pressure: Osmosis in Action
Plant cells have a large, central vacuole which is filled with water
This vacuole takes up much of the cell’s interior space
Water absorbed by the plants roots is stored in vacuoles
When a cell needs water for cellular processes, water moves from the vacuole to the parts of the cell where it is needed

9. This movement causes a decrease in the water in the cells cytoplasm, and an increase in the concentration of solutes
When solute concentration inside the plant cell becomes high, water moves into the cell by osmosis
When the vacuole and cytoplasm fill with water, this exerts pressure against the cell wall, and causes the cell to swell.
This outward pressure on the cell wall is called TURGOR PRESSURE.

10. When cells in the plant’s stem and leaves take in water, they become “turgid” – they stiffen and stay upright (a)

11. When cells in a plant’s stem and leaves lose water, the cells become less turgid, and the plant wilts (b)

12. Problems occur when plants lose too much water.
If the concentration of solutes increases in the soil – this lowers the concentration of water in the soil compared to the concentration of water in the plant roots
This causes water to move by osmosis from the plants roots to the soil
Why is this important to understand in the farming industry when dealing with fertilizers?

13. Exit Slip
Salting roads in the winter often results in a build up of salt, which causes the plant life beside the roads to die. Why are salty soil conditions not good for plants? Explain.