(2.17) Investigating diffusion and osmosis

Describe the agar experiment to investigate the effect of size on diffusion.

1. Cut up different sized cubes of agar. Calculate the volumes of each one.

2. Place the cubes in a beaker of 100cm³ food dye solution.

3. Leave the cubes for around 10-15 minutes.

4. Measure how far the dye has moved into the cube.

5. Calculate the volume of unstained agar for each cube.

What conclusions can be drawn from the agar experiment?

The larger the ‘cell,’ the longer even diffusion takes.

How could what we learn in the agar experiment be problematic for cells inside larger multicellular organisms?

The rate of diffusion may be too slow to reach the entirety of the space due to the smaller SA:V ratio.

Describe the potato practical to investigate effect of solution concentration on osmosis.

1. Prepare a range of sucrose solutions ranging from 0 mol/dm³ to 1 mol/dm³.

2. Set up 6 labelled test tubes with 10cm³ of each solution.

3. Use a cork borer and scalpel to cut 6 equal cylinders of potato.

4. Blot, weigh on a balance and record.

5. Put one piece into each test tube and leave for a set amount of time.

6. Remove the potatoes, blot and reweigh each piece.

7. Calculate percentage change.

What are the results of the potato experiment?

The piece in the 0 mol/dm³ will increase the most as the conc. gradient is greatest- this will be very turgid.

The piece in the strongest sucrose solution will lose the most mass as the water will have travelled from the potato to the concentrated solution- this will be flaccid.