Measuring the effect of environmental factors on water uptake
Investigating factors that affect the rate of transpiration
Insufficient water affects the yields of crops. Different factors affect The loss of water from leaves by evaporation through the stomata. and therefore water uptake. They can be investigated using a potometer.
Laboratory experiments are designed to simulate conditions a plant may encounter:
| Condition | When encountered by plant | How the condition is produced in a laboratory |
| Air movement | Windy conditions | Fan |
| Coatings on leaves that block stomata | Airborne pollution. Horticultural use on cuttings and Christmas trees. | Smear leaf surface(s) with petroleum jelly |
| High light intensity | Sunny climates. Artificial lighting in greenhouses. | Artificial lighting |
| High temperature | Warm and hot climates, greenhouse | Heater or greenhouse |
| Condition | Air movement |
|---|---|
| When encountered by plant | Windy conditions |
| How the condition is produced in a laboratory | Fan |
| Condition | Coatings on leaves that block stomata |
|---|---|
| When encountered by plant | Airborne pollution. Horticultural use on cuttings and Christmas trees. |
| How the condition is produced in a laboratory | Smear leaf surface(s) with petroleum jelly |
| Condition | High light intensity |
|---|---|
| When encountered by plant | Sunny climates. Artificial lighting in greenhouses. |
| How the condition is produced in a laboratory | Artificial lighting |
| Condition | High temperature |
|---|---|
| When encountered by plant | Warm and hot climates, greenhouse |
| How the condition is produced in a laboratory | Heater or greenhouse |
Question
When investigating the effect of light intensity on water uptake, what are the control variables?
Temperature, no air movement or draughts. It is also important to use the same species of plant, and shoots with a similar leaf surface if different plant shoots are used.
Example results
Here is a graph with some data collected from four laboratory experiments on factors affecting water uptake by a plant.
Question
Under which conditions is the rate of transpiration greatest?
At high temperatures. The graph indicates the greatest rate of transpiration has the steepest gradient.
Question
What is the rate of movement of the bubble in the potometer when the air is moved by the fan?
6.8 mm/min.
This could be calculated from 205 ÷ 30, or use any other two points:
Start value of x = 0 minutes
Start value of y = 0 millimetres
End value of x = 30 minutes
End value of y = 205 millimetres
\(\text{Gradient of line} = \frac{\text{increase in y}}{\text{increase in x}}\)
\(= \frac{(205 - 0)~\text{mm}}{(30 - 0)~\text{min}} = 6.8~\text{mm/minute}\)
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