Insufficient water affects the yields of crops. Different factors affect transpiration 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 the 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||Heater or greenhouse|
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.
Here is a graph with some data collected from four laboratory experiments on factors affecting water uptake by a type of plant.
Under which conditions is the rate of transpiration greatest?
At high temperatures. The graph indicates the greatest rate of transpiration has the steepest gradient.
What is the rate of movement of the bubble in the potometer when the air is moved by the fan?
This could be calculated from 205 ÷ 30, or use any other two points.
Calculate the gradient:
Value of x = 0 minutes
Value of y = 0 millimetres
Value of x = 30 minutes
Value of y = 205 millimetres