Variables
Controlled variables are maintained at a constant
Apparatus
1 x 1 Potometer
1 x 1 fan
2 x 1 retort stand and clamp
1 x 1 stop watch
1 x 1 thermometer
1 x 1 Balsam leafy shoot
1 x 1 beaker
1 x 1 candle
1 x 1 match box
1 x 1 30 cm ruler
1 x 2 syringe with needle
50 ml DCPIP
1 x 1 black polythene bag
1 x 1 rubber bung
Method
- The apparatus was set up as shown on the protocol diagram.
- The conical filter flask was filled with water.
- The leafy shoot was transferred from the water filled beaker to the sink and a slanting cut was made few centimeters above the last cut in water.
- The shoot was fit into the bung of the flask under water and pushed in to make a tight fit.
- The end of the rubber bung with wax was sealed using a candle and matches.
- DCPIP, the indictor, was inserted into one end of the graduated capillary tube using a syringe.
- The shoot was left to equilibrate for 5 minutes as it adjusts to its external conditions whilst regularly replacing the water taken up.
- The time taken for the water to move 30 cm along the capillary tubes were measured every 2 minutes.
- When the blue indicator reached the end of the graduated section of the tube, it was returned to its original position using a syringe.
- Steps 7 to 9 were repeated for windy conditions, dark conditions, and for when half the leaves were removed.
- Results obtained are tabulated and a graph is drawn to compare the rate of uptake of water over a certain period of time.
Protocol diagram
LEAFY SHOOT
RETORT STAND
SYRINGE
RUBBER BUNG
GRADUATED CAPILLARY TUBE
WATER
CONICAL FLASK RUBBER TUBING
Figure 1 showing the protocol diagram of the potometer
Photo’s of setup in normal, dark and half the leaves removed
Figure 1 showing half the leaves removed
Figure 2 Showing dark conditions
Data collection
Table containing raw data & processed data
No further readings could be obtained for transpiration in windy conditions, dark conditions and for when half the leaves were removed because the indicator had already reached the end of the capillary tube, thus having moved 30cm in the lapse of 16 minutes and 22 minutes respectively.
Error analysis
Thermometer: ± 0.5°C
Conclusion
It can be concluded that when the leafy shoot was exposed to windy conditions, the rate of water uptake has increased. This can be explained by the fact that the air currents have removed the water vapour surrounding the shoot, opening stomatal pores and thus increasing a rate of transpiration.
When the shoot was enclosed in a dark plastic bag, the rate of water uptake increased considerably. My hypothesis regarding the rate of uptake in dark conditions needs to be refuted. This could have been due to the fact that the experiment was done during 10am and 1pm (the hottest time of the day). This in turn increased the transpiration rate of the plant; so instead of a slow water uptake, there was a relatively faster one. The length moved after 2 minutes was 5.5 cm and after 6 minutes it had increased to 13.5.
When half the leaves were removed, there was a rapid uptake of water at first. However, as the plant equilibrated to the new conditions, the rate of water uptake decreased gradually.
Evaluation
My investigation aimed at showing the impact of different external factors on the rate of water uptake by a leafy shoot; in this case, a shoot from the Balsam plant was taken. The experiment took roughly about 3 hours 30 minutes to complete as the set up of the equipment took a lot of time as well as the preparation of the shoot and adjustments which had to be made to limit air loss from the rubber bung.
An unbalance in the pressure between the potometer and the graduated capillary tube would disrupt cohesion tension in the shoot. Seeing as only 3 environmental conditions were tested, a broader understanding of the effect of external factors on the rate of water uptake by a leafy shoot would be possible if other conditions were tested for, such as humidity, increased light intensity and vaselining the upper and lower epidermises of the leaves.
More readings over a longer period of time could have been taking to obtain more accurate average. Moreover, an estimate of the water loss per unit in leaf area could have been derived by measuring the volume of water lost and then removing all the leaves in order to determine the surface area.
Overall, I would have preferred looking at more factors which could have influenced the rate of water uptake by the Balsam leafy shoot, but because of time restraints I could not do so. It was interesting to see how external factors affect the rate of transpiration in plants.