91�ȱ�

Use a potometer (bubble and weight potometer) to investigate the factors affecting the rate of water uptake by a plant.

Bubble potometer procedure

1. Set up a bubble potometer (under water and using petroleum jelly).
2. Note the position of the bubble.
3. Leave for a period of time.
4. Note the new position of the bubble.
5. Calculate the rate of bubble movement over this period of time.
6. Reset the apparatus.
7. Repeat steps 2-6 under the same conditions to increase the reliability of the experiment.
8. Adjust the environmental conditions.
9. Repeat steps 2-7 for the new environmental condition.
10. Record results in a table.

Weight potometer procedure

1. Set up a weight potometer.
2. Measure the mass of the container and plant.
3. Leave for a period of time.
4. Measure the new mass of the container and shoot.
5. Calculate the rate of change of mass over this period of time.
6. Repeat steps 1-5 under the same conditions to increase the reliability of the experiment.
7. Adjust the environmental conditions.
8. Repeat steps 1-6 for the new environmental condition.
9. Record results in a table.

Practical 2.2

Use the washing line method to investigate the factors affecting the rate of water loss from leaves.

Procedure

1. Remove a number of leaves from a plant.
2. Smear petroleum jelly over the cut stalks to make them waterproof.
3. Measure the mass of each leaf.
4. Using paperclips hang the leaves on a line of string (held up by 2 retort stands).
5. If investigating the effect of temperature on water loss by a leaf, hang half of the leaves at a high temperature and the other half at a low temperature.
6. After a period of time, find the new mass of each leaf.
7. Calculate the average loss of mass at each temperature.