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• PHOTOSYNTHESIS AND LIGHT

  Aim:

  To experimentally prove that photosynthesis only occurs in the light.
• PHOTOSYNTHESIS AND LIGHT

  Method:

  1. Half cover a geranium plant leaf (or similar) with silver foil.
  2. Place the plant on a sunny windowsill for 48 hours.
  3. Drop the leaf into boiling water to kill and preserve it.
  4. Then place it in hot ethanol in a boiling tube for ten minutes to remove the chlorophyll.
  5. Dip the leaf in boiling water to soften it.
  6. Spread the leaf out in a Petri dish and covered with iodine solution.
  7. Record which areas remain the brown colour of the iodine stain and which are changed to blue/black as a result of the presence of starch.
• PHOTOSYNTHESIS AND LIGHT

  Risks:

  • Care must be taken when using boiling ethanol.
  • Make sure that no Bunsen burners are turned on as the ethanol is highly flammable.
• PHOTOSYNTHESIS AND LIGHT

  Results:

  • The half of the leaf under the silver foil remained the brown colour of the iodine stain.
  • This is because no photosynthesis occurred, so no glucose was produced and none was stored as starch.
  • The half of the leaf not covered by the silver foil turned blue/black in the presence of iodine.
  • This proves that glucose was produced during photosynthesis and was stored by the plant as starch.