Measuring water uptake - potometers

• The stem, root and leaves form an organ system that transports substances into, around and out of a plant.
• Plant cells, tissues and organs are adapted to their functions.
• The need for transport in plants is crucial for survival.
• Transpiration is a process that occurs in plants.
• Factors affecting transpiration include environmental conditions such as temperature and light intensity.
• Investigating transpiration involves measuring the rate of water uptake in plants.
• The uptake of water can be measured using a potometer.
• A simple potometer is a piece of capillary tubing to which a plant has been connected.
• The distance moved by the bubble is 3.2 mm/minute.
• The gradient/rate is calculated from the line of best fit and not from the table of data.
• The gradient of the graph is calculated by choosing any two points on a straight line and calculating the increase in y over the increase in x.
• A compound measure is made up of two or more other measurements, for example, the rate of water loss is a compound measure because it is made up of water loss in grams and time in minutes.
• When a plant is short of water, it has wilted, the rate of water uptake will not equal the rate of transpiration.
• The rate of water uptake is best found using the gradient of the graph.
• The water uptake is measured by recording the time taken for a bubble in the tube to move a set distance.
• The aim of the experiment is to find the rate of water uptake of a plant.
• The method involves cutting a shoot from a woody plant, submerging the end of the shoot under water to ensure that the xylem remains water-filled and prevents air locks, inserting the shoot into the rubber tubing at the end of the potometer, raising the potometer so that a bubble of air is taken up, and lowering the potometer into water.
• The distance travelled by the air bubble is recorded over a period of time.