Practical 14 - Investigation into transpiration using a simple potometer

Question 1

What causes after to be absorbed by the plant and moved through the xylem vessels to the leaves?

Answer 1

The loss of water from the leaves of the plant

Question 2

Which vessels does water move up through in a plant?

Answer 2

Xylem vessels

Question 3

What’s the name of the upward movement of water through a plant?

Answer 3

The transpiration stream

Question 4

Transpiration

Answer 4

Evaporation go water from the leaves (mainly through the stomata) to the atmosphere

Question 5

Is the rate of uptake of water equal to the rate of evaporation of water from the leaf? Why?

Answer 5

No
Very small volumes of water are used in physiological processes (e.g - photosynthesis typically uses less than 1% of total water as a reactant)

Question 6

What does this method give us?

Answer 6

A reasonable approximation of the transpiration rate

Question 7

Which factors is the rate of transpiration effected by?

Answer 7

Temperature
Light
Humidity
Wind
Atmospheric pressure

Question 8

Draw and label the potometer set up

Answer 8

(See notes)

Question 9

What is the method of this practical?

Answer 9

1. Immerse the potometer completely under water and assemble it under water to prevent any air bubbles from entering
2. Put the cut end of the stalk (not the leaves) of your plant under water and cut off the last centimetre of the stalk diagonally underwater
3. With the potometer and stalk still underwater, push the stalk into the potometer as shown - should fit tightly + ensure that there’s no air bubbles in the system + no air can be sucked into the apparatus around the stalk
4. Remove the plant and potometer from the water
5. Apply Vaseline to the joints to prevent air entering
6. Gently dab the leaves with a paper towel to remove excess water
7. Clamp the potometer in an upright position with the end of the capillary tube under the water in the beaker
8. Remove the capillary tube from the water and let an air bubble form
9. Replace the end of the capillary tube under water
   10.when the air bubble reaches the scale, record ow far the air bubble travels in a known time
10. Repeat stages 8-10 twice
11. Record results in a table
12. Record the internal diameter of the capillary tube - can express results in the form of cm^3 water lost per minute
    Volume of water uptaken by leafy shoot
    Pi x r^2h (h = distance moved by air bubble)
13. Remove the leaves, place onto graph paper, draw around the edge of each leaf and calculate the total surface area of the leaves
14. Express your final rate of transpiration as the volume of water list per cm^2 per minute

Question 10

Equation for calculating the volume of water uptaken by leafy shoot

Answer 10

Pi x r^2h
Where h = the distance moved by air bubble

Question 11

How do we make an air bubble form?

Answer 11

Place the end of the capillary tube under the water in the beaker
Remove the capillary tube from the water and let an air bubble form
Replace the end of the capillary tube under water

Question 12

Why do we apply Vaseline to the joints?

Answer 12

To prevent air from entering