Osmosis.

Osmosis Definition : 

Osmosis is the NET movement of water particles from an are of high concentration of water to an area of low concentration of water across a semi-permeable membrane.

Potato Experiment

• Cut 6 equal pieces if potato, ensuring they have the same surface area and the exact mass to 2 dp
• Place each piece in a boiling tube and cover with 20ml of solution, each tube containing a different sugar/water content
• Leave for as long as possible and measure with a stopwatch.
• Take each piece out and blot dry with paper.
• Find the new mass of the pieces of potato and calculate the charge in mass.

The piece that did not change in mass must have the same water content as the solution. If the piece in 10% sugar solution remained the same then the potato must be 90% water, as there was no change in mass so no NET movement of water from the potato  to the solution or solution to the potato. The potato and the solution are ISOTONIC

OSMOSIS IN CELLS:
- how does osmosis affect cells?

• the cell membrane seperates the contents of the cell from the outside. It has holes in it. This allows small molecules to pass through it but not large molecules.

- osmosis in plant cells

• normal cell wall, made of cellulose - it keeps it's shape.
• Put in a sugar solution, the water is taken from the cell and becomes plasmolyed (smaller vacuole)
• Put in water, the vacuole increases. The cell is turgid.

Unlike animal cells, the plant cell has a cell wall which stops it from swelling and bursting.

- osmosis in plant cells

Animal cells do not have a cell wall. This means they either swell and burst or shrink if too much water leaves.