Aim
To demonstrate the process of photosynthesis in plants and test the presence of starch in a leaf.
Materials Required
- Beaker
- Test tube
- Leaf from a potted plant kept in sunlight
- Boiling water
- Alcohol (ethanol)
- Water bath (to safely heat ethanol)
- Iodine solution
- Forceps
Image Reference
Procedure
- Select a leaf from a potted plant that has been exposed to sunlight for several hours.
- Boil the leaf in water for 2-3 minutes using a beaker. This softens the leaf and kills it, stopping all metabolic processes.
- Using forceps, transfer the boiled leaf into a test tube containing ethanol. Place the test tube in a water bath and heat it until the leaf becomes decolorized (removal of chlorophyll).
- Remove the leaf carefully and rinse it in cold water to soften it and make it more pliable.
- Place the leaf on a white tile and add a few drops of iodine solution to it. Observe the color change.
Observation
The part of the leaf exposed to sunlight turns blue-black after adding iodine solution, indicating the presence of starch. Any part of the leaf that was not exposed to sunlight remains yellow-brown, showing the absence of starch.
Inference
This experiment demonstrates that:
- Photosynthesis occurs in the presence of sunlight, leading to the production of starch as a byproduct.
- Chlorophyll is essential for photosynthesis, as it traps sunlight needed for the process.
Precautions
- Ensure the potted plant is exposed to sunlight for sufficient time (at least 4-6 hours) before performing the experiment.
- Handle ethanol with care as it is flammable. Always use a water bath for heating ethanol.
- Use forceps to handle the hot leaf to avoid burns.
- Rinse the leaf thoroughly after boiling in ethanol to remove traces of alcohol that might interfere with the iodine test.