Transpiration - Practical Skills

Question 1

What is the function of a potometer?

Answer 1

A device used to measure the rate of water uptake of a plant, and hence the rate of transpiration

Question 2

Which factors affect the rate of transpiration?

Answer 2

• Temperatrue
• Surface area
• Wind speed
• Light intensity

Question 3

Why must the leafy shoot be cut underwater?

Answer 3

To prevent air bubbles from forming in the vascular tissue

Question 4

Outline the procedure to this practical

Answer 4

• Set up the potometer
• Clamp the capillary tube into the stand. Place the bottom of the capillary tube into the beaker of water
• Smear petroleum jelly around ht join to maintain airtight conditions
• Leave for 5 minutes for a bubble to be drawn into the capillary tube
• Measure the movement of the bubble along the capillary tube in a certain length of time
• Repeat the experiment and change the abiotic variable

Question 5

How is the rate of transpiration calculated?

Answer 5

• Measure the distance travelled by the bubbles in the capillary and the radius of the capillary
• Find the volume of water taken up by using π r²
• Divide the volume by time

Question 6

How is light intensity controlled?

Answer 6

By changing the distance between the lamp and the potometer

Question 7

How can wind speed be controlled?

Answer 7

By placing a fan near the potometer with different speeds

Question 8

How can humidity be controlled?

Answer 8

By warping a plastic bag around the plant to maintain a humid environment

Question 9

What are some limitations of this method?

Answer 9

• Not all of the water taken upon is transpired, some is used to maintain turgidity and for photosynthesis
• The plant is dying when the stem is cut, rate of water uptake is lower than normal