Transpiration

Question 1

Why is a continuous movement of water through a plant necessary ? (3)

Answer 1

• Photosynthesis – It ensures that there is a constant supply of water to the leaves where it is used in photosynthesis
  • Transport of minerals – Any dissolved minerals can be moved through the plant to where they may be needed
  • Support – The movement of water into cells by osmosis provides support

Question 2

What does a :
- potometer
- bubble potometer 
- weight potometer 
- washing line method 
Do?

Answer 2

• A potometer measures water loss from leaves.
• A bubble potometer measures the rate of water loss from a plant by transpiration.
• A weight photometer measures the amount of water lost by a plant through transpiration.
• The washing line method is used to prove that most water loss occurs from the lower surface of the leaf.

Question 3

Why is it necessary to cut the shoot under water?

Answer 3

• Cut the shoot under water to prevent air bubbles entering the xylem of the stem and ensure the cut is diagonal to increase the surface area available for water uptake.

Question 4

Why is the cut shoot and potometer sealed with Vaseline ?

Answer 4

To ensure that no oxygen enters the system

Question 5

Why is it necessary to dry the leaves for the bubble potometer?

Answer 5

This will create a concentration gradient

between the inside and outside of the leaves

Question 6

How are the effects of different abiotic factors measured on the bubble potometer ?(4)

Answer 6

• reset the bubble using the syringe and repeat the experiment with
• a heat lamp shining on the leaf (temperature)
• fan blowing air around the leaf (windy conditions)
• with a lamp and fan (humidity?)

Question 7

Suggest another investigation to measure the effect on water uptake

Answer 7

Surface area- cut some leaves from the plant

Light intensity - from distance of the lamp from the plant

Question 8

Why is a layer of oil used in the weight potometer ?

Answer 8

• Pour a layer of oil onto the water to prevent evaporation from the surface.

Question 9

Conclusion about weight potometer

Answer 9

Over time water in the measuring cylinder will be pulled through the plant to the leaves where it will evaporate. So the overall amount of water in the cylinder will decrease. This will be shown as a decrease in weight.