3.6 Osmosis

Question 1

What is osmosis?

Answer 1

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

Question 2

What is meant by ‘water concentration’?

Answer 2

The amount of water, as compared to other molecules, like sugars or salts (solutes) that are dissolved in the water

Question 3

What would happen to red blood cells if they were placed in pure water?

Answer 3

They would gain water and swell

Question 4

Describe the steps to observe the effect of sugar solutions on plant tissue (5)

Answer 4

1) You cut up a potato into identical cylinders, and 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. 1mol/dm). Then you can have a few others with concentrations in between (e.g. 0.2 mol/dm, 0.4 mol/dm, 0.6mol/dm, etc.)
2) You measure the mass of each cylinder, then leave one cylinder in each beaker for 24 hours or so. (Alternatively, you could measure the length of each cylinder.)
3) After taking the cylinders out, dry them with a paper towel and measure their masses again
4) The only thing that should change in this experiment is the concentration of the sucrose solution. Everything else (e.g. the volume of solution, the time the cylinders are left for, the temperature, etc.) must be kept the same or your results won’t be valid.
5) Once you’ve got your results you can calculate the percentage change in mass for the cylinders in each beaker, plot a graph and analyse your results.