Experiment: Measuring the Rate of Transpiration

Question 1

what is a potometer?

Answer 1

a potometer is a device used to estimate transpiration rates

Question 2

how can a potometer be used to work out water uptake by the plant?

Answer 2

the distance moved by air bubble can be recorded every minute and used to indicate the rate of water uptake by the plant

Question 3

what is a potometer used for?

Answer 3

to measure the rate of water uptake from a leafy shoot - as 90% of this water is transpired, we use this as a measure of the rate of transpiration

Question 4

how to set up a potometer

Answer 4

1. the potometer must be set up under water - this prevents any air bubbles from entering the system and blocking the xylem
2. cut the stem of the shoot
3. put the shoot stem into the bung, grease the joint with petroleum jelly - this prevents water loss and air entry
4. put the bung into the potometer
5. make sure the tap is closed and it is full of water (no bubbles) - then lift the potometer out of the water
6. leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water
7. you can measure the transpiration rate as the distance the bubble travels in five minutes - you should take a number of readings and calculate a mean rate

Question 5

how can you demonstrate the importance of the stomata in transpiration experiment?

Answer 5

remove the leaves off the plant or cover them in vaseline