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Effect of Chlorophyll on Photosynthesis


To test the relationship between the presence of light and photosynthesis.

HOW DOES IT WORK?                                                    

Preparation Time: 24 hours
Time allocation: 35 Min

The hot water will kill the leaf, where photosynthesis has taken place, and the alcohol will break down and remove the chlorophyll form the leaf sample. Chlorophyll is the green pigment that is responsible for the photosynthesis in plants. Iodine reacts with starch to form a blue-black colour. Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue-black with iodine solution, showing the importance of chlorophyll in photosynthesis.

Note that ethanol is heated using a hot water bath. Ethanol boils at 78° C it is advisable to make use of the water bath instead of a Bunsen burner because ethanol is flammable if it gets heated rapidly by a direct flame.


  • 1 x 250ml Glass beaker
  • 1 x 100ml Glass beaker
  • 100ml Ethyl Alcohol (Ethanol)
  • 10ml Iodine solution
  • 1 x forceps
  • 1 x Watch glasses
  • strip of foil
  • 1 x Paperclip
  • 1 x Gas stove and fuel cartridge
  • 1 Gauze wire

To be supplied by Educator

  • Various leaf samples ( variegated, coloured and plain green)


  1. Place 100ml of water into a 250ml beaker and bring to a boiling on the Bunsen burner.
  2. Dip the individual leaf in boiling water for 60 seconds, using the forceps.
  3. Remove the leaf from the boiling water.
  4. Put about 25-50ml of ethyl alcohol in a 100ml beaker.
  5. Place the beaker in the boiling water, with the heat turned off.
  6. Place the individual leaf in the ethyl alcohol for 2 minutes or until they turn almost white in colour.
  7. Place leaf sample on the spotting tile.
  8. Drop a few drops of Iodine solution on each the leaf sample. The green part of the leaf will turn blue-black, indicating the presence of starch. The starch dropped on the yellow/ white part of the leaf will not change colour (will dye the leaf brown), indicating the absence of starch.


The experiment proved that photosynthesis is a chlorophyll dependent process. This means that green parts of the leaf photosynthesized but the other various coloured parts of the leaf did not, due to the presence of starch in areas where chlorophyll was green but not where other areas of the leaf were discoloured.


  • Students and educator may not leave any open flame unattended
  • Chemicals must be stored correctly
  • Ingestion or inhalation of any chemicals is dangerous
  • When removing a hot glass apparatus off the heat , place on a surface which conducts heat well (e.g. chopping board or wood surface) to prevent it from shattering
  • Ethyl Alcohol (Ethanol):
    • Do not ingest. If it is, do not induce vomiting or ingest milk, seek professional medical attention immediately.
    • Do not smell while boiling.
    • If contact is made with skin wash with water immediately.
    • If splashed in eye , rinse eye with water and seek professional medical attention immediately
  • Iodine Solution:
    • In presence of light Iodine solution undergoes a photo-decomposition reaction so it must be stored in a dark bottle, generally in amber bottle to minimize the amount of light that the solution is exposed to. If stored in a clear bottle it will gradually break down as the iodide ions which are gradually converted to iodine and the solution turns a yellowish color.