CP8: using a potometer to investigate the effect of environmental conditions on water uptake in a plant shoot

potometer

device that measures uptake of water + rate of transpiration, in a leafy shoot

what can rate of transpiration be affected by?

• light intensity

• humidity

• wind speed

• temp

how do you use the potometer?

1. lay capillary tube and rubber connector under water and fill both parts

2. keep shoot underwater and insert it into rubber connector - all under water

3. smear petroleum jelly around the join between the shoot and rubber connector to ensure airtight seal

4. leave for 5 mins to allow bubble to be drawn up

5. dry the leaves by blotting them gently with paper towels

6. measure the time take it takes in seconds for the air bubble to travel a set distance

7. convert measurement into rate of transpiration

8. repeat experiment + change abiotic variable

how does temp affect rate of transpiration?

• increases the rate of diffusion + evaporation from stomata

how does light intensity affect rate of transpiration?

affects rate of photosynthesis, which affects no. of stomata which are open

how does humidity affect rate of transpiration?

affects rate of diffusion + evaporation by decreasing conc. gradient between plant + atmosphere

how does wind speed affect rate of transpiration?

increases conc. gradient by mechanically removing water from outside the stomata.

dependent variable

time it takes for air bubble to move a set distance - used to calculate rate of transpiration

potometer set up

why do you assemble the ptometer underwater

cutting and assembling underwater prevents air bubbles from entering the xylem where they could block the movement of water

potroleum jelly

seals the join to make it airtight

why do you dry the leaves of the shoot

water on the leaves will block the stomata and affect transpiration

allow a single airbubble to form inside potometer and place the end of the tube into a beaker of water

• air bubble allows water movement in the tube to observed

• the beaker of water provides a supply of water to replace water that is lost

how can you test the different environemntal factors?

• ariflow: set up a fan or hairdryer with different speeds

• humidity: spray water in a plastic bad and wrap around the plant

• light intensity: change the distance of a light source from the plant

• temperature: carry out the experiment in a cold room amd warm room