osmosis

What is osmosis?

The net movement of water molecules across a semi permeable membrane from a region of higher water concentration to a region of lower water concentration

What is osmosis a type of?

Diffusion- passive movement of water molecules from an area of higher concentration to an area of lower water concentration

What determines the concentration?

The proportion of water :solute

What is water concentration?

Amount of water (compared to other molecules like dissolved sugars or salts (solutes)

What happens if a cell is short of water?

The solution inside it will become quite concentrated(there’ll be a low concentration of water molecules) this usually meajs that the solution outside the cell is more dilute(there’s a higher concentration of water molecules) so water will move into the cell by osmosis

What happens if a cell has lots of water?

The solution inside it will be more dilute and water will be drawn out of the cell and into the fluid outside by osmosis

What will happen when the solution surrounding a cell usually has a different concentration to the fluid inside?

Water will either move into the cell from the surrounding solution or out of the cell by osmosis

Explain the required practical for investigating the effect of sugar solutions on plant cells?

1) Cut up a potato into identical cylinders and measure their masses

2) Get some beakers with different sugar solutions in them one should be pure water and another should be a very concentrated sugar solution (E.G.1.0 mol/dm3). Then you can have a few others with concentrations in between (E.g.0.2 mol/dm3, 0.4 mol/dm3, 0.6 mol/dm3 etc).

3) place one potato cylinder in each beaker. Leave them in the beaker for 24 hours

4) Take the cylinders out, dry them with the paper towel and measure their masses again

5)If the cylinders have drawn in water by osmosis they’ll have increased in mass. If Water has been drawn out, they’ll have decreased in mass. You can calculate the percentage change in mass then plot a few graphs.

What are the variables in the investigation?

Dependant- cylinder mass

Independent- the concentration of sugar solution

Control-volume of solution, temperature, time, type of sugar used

Errors in RP? And how to reduce

If some mass or water evaporated from the beakers the concentration of the sugar solution is would change

You can reduce the effect of these errors by repeating the experiment and calculating a mean percentage change at each concentration