2.3 potometer Flashcards
1
Q
transpiration
A
water loss from aerial parts of the plants- leaves due to diffusion and evaporation
2
Q
what is potometer used for
A
to measure the rate of water uptake from shoot
small amount of water is used in photosynthesis or to maintain turgidity
the rate of water uptake is equal to rate of transpiration
3
Q
equipment
A
● Cut shoot
● Potometer
● Scissors
● Beaker of water
● Vaseline
● Clamp stand
● Stopwatch
4
Q
hazard
A
broken glass
scissors
5
Q
precaution- broken glass
A
keep glassware away from edge of desk
6
Q
precaution scissors
A
handle scissors with care
keep away from edge of desk
7
Q
risks
A
cut skin
8
Q
method
A
- Construct the potometer underwater. This stops the entry of air bubbles.
- Immerse the end of the cut shoot underwater and using a pair of scissors, cut the last centimeter off at an oblique angle. Cut underwater to prevent the entry of air bubbles into the xylem. Cut at an oblique angle to increase the surface area for water absorption.
Ensure that the leaves of the shoot remain dry to prevent the obstruction of stomata by water droplets. - Whilst still underwater, insert the shoot tip into the rubber tubing of the potometer. The shoot tip must perfectly fit the rubber tubing to prevent the entry of air and formation of air bubbles.
- Remove the apparatus from the water and grease all joints with Vaseline to give a tight seal. This prevents air entering.
- Leave the cut shoot in the potometer for 10 minutes to allow it to equilibrate.
- Clamp the potometer so that the end of the capillary tube is immersed under water.
Remove the end from the water to allow an air bubble to form. Reimmerse and seal the
capillary tube. - Note the starting position of the bubble on the volume scale. Start the stopwatch and record the distance travelled by the bubble in a set period of time (e.g. 10 minutes).
- Repeat steps 6 to 7 a further two times to obtain three repeats.
9
Q
A
