Investigating transport in plants

Question 1

Describe the use of tracers in investigating transport in plants

Answer 1

1. Leaf supplied with a radioactive tracer eg. CO2 containing radioactive isotope 14C
2. Radioactive carbon incorporated into organic substances during photosynthesis
3. These move around plant by translocation
4. Movement tracked using autoradiography or a Geiger counter

Question 2

Describe how aphids can be used in investigating transport in plants

Answer 2

Aphids pierce the phloem using mouthpiece

Releasing sap from plants

Flow of sap higher at source than sink

Evidence of a pressure gradient; higher pressure near source

Question 3

Describe how a metabolic inhibitor can be used in investigating transport in plants

Answer 3

Add a metabolic inhibitor to phloem
-translocation stops
-proves that active transport is involved
- as it requires ATP to move against a conc gradient

Question 4

Potometer

Answer 4

estimates the transpiration rate by measuring water uptake.

Question 5

How to carry out potometer

Answer 5

1. Cut a shoot underwater at a slant →
   prevent air entering xylem
2. Assemble potometer with capillary tube
   end submerged in a beaker of water
3. Insert shoot underwater
4. Ensure apparatus is watertight / airtight
5. Dry leaves and allow time for shoot to
   acclimatise
6. Shut tap to reservoir
7. Form an air bubble - quickly remove end
   of capillary tube from water

Question 6

What factors affect the rate of transpiration

Answer 6

Light
Wind
Humidity
Temperature

Question 7

How does light affect transpiration

Answer 7

The higher the light intensity, the faster the transpiration rate .Because stomata open in light to let in CO2 for photosynthesis
Allowing more water to evaporate faster
Stomata close when it’s dark so there is a low transpiration rate

Question 8

Explain how temperature affects the rate of transpiration

Answer 8

The higher the temperature, the faster the transpiration rate
Water molecules gain kinetic energy as temperature increases
Move faster
Water evaporates faster

Question 9

Explain how humidity affects the rate of transpiration

Answer 9

The lower the humidity, the faster the transpiration rate
Because as humidity increases, more water is in the air so it has a higher water potential
Decreasing the water potential gradient from leaf to air
Water evaporates slower

Question 10

Explain how wind affects the rate of transpiration

Answer 10

The windier, the faster the transpiration rate
Wind blows away water molecules from around the stomata
Decreasing the water potential of the air around the stomata
Increasing the water potential gradient
Water evaporates faster