TRANSPIRATION

• INVESTIGATING TRANSPIRATION:

  A simple method for investigating water loss from plant leaves is to measure their change in mass over a period of time.

  Various factors that affect water loss from the leaf can be investigated using this method, for instance:

  • air movement – direct a fan on the leaves
  • temperature
  • obstructing the stomata, eg with petroleum jelly
• TRANSPIRATION INVESTIGATION:

  Method

  1. Remove a number of leaves from a bush or tree.
  2. Find the mass of each leaf.
  3. Suspend each leaf from a piece of wire or string.
  4. After a set period of time, re-measure the mass.
• ANALYSIS OF RESULTS:

  TRANSPIRATION INVESTIGATION:

  • There may be variation in the decrease in mass of different leaves.
  • It is important to repeat the experiment and calculate a mean for each set of data.
• INVESTIGATING TRANSPIRATION:

  WATER LOSS THROUGH THE STOMATA-

  • Water is lost through open stomata. Scientists can't count all the stomata on a leaf surface as there are too many to count so they take a representative sample - give a true picture of the numbers of stomata on the leaf.

  To be representative of the whole leaf, the representative sample must:

  • include a sufficient number of counts of stomata over different parts of the slide
  • must be random, and not select areas where there are many or few stomata
• 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.
• POTOMETER:

  Aim of the experiment

  To find the rate of water uptake of a plant.
• POTOMETER

  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
• POTOMETER:

  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.
• POTOMETER:

  RESULTS-

  The rate of water uptake is best found using the gradient of the graph of results.

  The most accurate results will be obtained if these points are as far apart as possible.