Measuring water uptake - Potometers

Investigating transpiration

The uptake of water can be measured using a potometer. Under normal circumstances, the rate of water uptake gives a measure of the rate of transpiration.

A simple potometer is a piece of capillary tubing to which a plant has been connected. The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance.

Aim of the experiment

To find the rate of water uptake of a plant.

Diagram of how to conduct an experiment of how to find the rate of water uptake in a plant

The potometer is filled with water.

Variables

  • independent variable - time
  • dependent variable - the distance moved by the bubble along the capillary tube
  • control variables - temperature, air flow or draughts, adequate supply of water

Risks

Care must be taken when inserting the plant shoot into the rubber tubing attached to the capillary tube and with the scissors used to cut the plant shoot.

Example results

Time in minutesDistance moved by bubble in mm
00
516
1032
1547
2064
2580
3095

Analysis of results

Plot a line graph of the data.

Graph showing the rate of water uptake