Osmosis is the net movement of water molecules across a partially permeable membrane from a region of high to low water concentration
A partially permeable membrane is one that allows some small substances such as water to pass through it but not others such as glucose
A solution with higher water concentration is a dilute solution
A solution with lower water concentration is a concentrated solution
Osmosis only considers the movement of water molecules, so even if there is a higher concentration of overall particles on one side, if the other side has more water molecules it has a higher water concentration
Water potential is the likelihood that water will diffuse into or out of a cell.
If it has a low water potential, then it has a low concentration of water molecules
Watering a plant increases the water potential around it. This mean the plant cells draw water by osmosis until they become turgid
If there is no water in soil, the plant starts to wilt. This is because the cells become flaccid
When a plant becomes turgid, the contents of the cell push against the cell wall - this is called turgor pressure. This helps support the plants tissues
If water moves into a cell, its mass will increase. It will lose mass if water leaves the cell
Investigating the effect of a range of concentrations of sugar solutions on the mass of a plant
Place six boiling tubes in a rack. Label them with different salt concentrations
To boiling tubes add 20ml of appropriate solution
Using balance, record mass of each potato cylinder, keeping track of which cylinder is which
Place each potato cylinder in a boiling tube
After 30 minutes, dry the potato and reweigh them
If the same amount of particles are on both sides, there is no net movement
Crenated cell (hypertonic concentration)
When a cell is put in a solution with higherconcentration than the cells cytoplasm, water in the cytoplasm will move out and and cell will shrink
Lysed cell
When a cell is put into a solution with a higher concentration than the cells cytoplasm, water molecules will rush into the cytoplasm, causing it to swell and burst
Only animal cells can be crenated and lysed
Hypertonic - high concentration
Hypotonic - lower conentration
Isotonic - same concentration
Turgid (hypertonic)
Plant cells which have high water concentration due to absorbed water in the cytoplasm, so the cell membrane pushes against the cell wall, making the cell firm and swollen
Flaccid (isotonic)
Flaccid plant cells have lost water, resulting in low water concentration in the cytoplasm and reduced pressure against the cell wall. This causes the cell to become limp and wilted
Plasmolyzed (hypotonic)
Cells which have lost so much water that the cell membrane pulls away from the cell, potentially damaging the cell