Equipment;
- large leafy shoot with a woody stem
- capillary tubing with rubber connectors
- clamp stand
- stop clock
- 250 cm3 beaker
- fan
- metre ruler
- petroleum jelly
Safety;
- Take care when putting together potometer together, do not force parts together.
- Take care when cutting shoot
Method
- Select a leafy shoot, with a similar diameter to the rubber connector. Keep the shoot under water while you select and cut it.
- Submerge the capillary tubing, so that there are no air bubbles within the tubing.
- Insert the shoot into the rubber connector, make sure the fit is tight, then connect the rubber connector to the capillary tubing.
- Place the bottom of the capillary tubing into the beaker of water, smear all the joins with petroleum jelly to create an airtight seal.
- Lift out the potometer from the water, dry the leaves with a paper towel.
- Leave the system for 5 minutes.
- Place a metre ruler at the base of the leaves, pointing away from the tubing. Place the fan by the metre ruler.
- Make an air bubble at the start of the capillary tubing, make sure the air bubble is small.
- Place the fan at a distance of 0.3 metres from the leafy shoot. Turn the fan on.
- After a few minutes start the timer, measure the distance moved by the air bubble in 3 minutes.
- Repeat the experiment at different distances, repeating 3 times at each distance.
- After the results are taken, pull off the leaves and work out the surface area. Find the diameter of the capillary tubing.
Results
Table of results showing the volume of water taken up by the shoot in comparison to the distance from the fan
Table of results showing the rate of water uptake in mm3min-1
Table of results showing the volume of water taken up per area of the leaves per hour in mm3.m-2.hour-1
Questions
- An airtight seal is required so no pressure is lost within the system, as in a plant there is a transpirational pull on the water, therefore like the xylem the system needs to be closed. Therefore a seal is required to recreate the conditions in the plant.
- There were a few limitations in this experiment. The leaves on the shoot overlapped, therefore the surface area of the leaves should be less than the actual value I calculated. I also only used one plant, therefore I cannot compare my results to any others.
- If the surface area was made smaller to compensate for the overlapping the rate of uptake per m2 per hour would be greater than the actual values I got. To be able to compare with over results would allow me to draw a credible, reliable conclusion.
- To reduce the effects of the limitations I would have used a shoot with fewer leaves therefore I can more reliably calculate the surface area which faces the fan. Conducting the experiment over a greater range of distances would have allowed for a more valid conclusion to confirm the negative linear relationship.