This image describes an experiment to demonstrate that light is necessary for photosynthesis. Here is the method for conducting this experiment, along with the expected observations and conclusion.

This ensures that all the starch previously stored in the leaves is used up, so any starch detected later is newly formed during the experiment.

Cover a part of this leaf on both sides with aluminium foil or black paper, securing it with paper clips or tape, ensuring no light reaches the covered portion. Leave another part of the same leaf, or a different leaf, completely exposed to light.

*   Pluck the covered leaf from the plant.
*   Remove the aluminium foil or black paper from the leaf.
*   Boil the leaf in water for a few minutes to kill the cells and break down cell membranes.
*   Transfer the leaf to a test tube containing alcohol (ethanol) and place the test tube in a beaker of boiling water (using a water bath to avoid direct heating of alcohol, which is flammable). Boil until the leaf is decolorized (chlorophyll is removed).
*   Wash the decolorized leaf thoroughly with cold water to soften it and remove any residual alcohol.
*   Spread the leaf on a white tile or petri dish and add a few drops of iodine solution to its surface.

Observations:

• The portion of the leaf that was exposed to sunlight (uncovered) turns blue-black when iodine solution is added.
• The portion of the leaf that was covered with aluminium foil or black paper (not exposed to sunlight) remains yellowish-brown (the color of the iodine solution).

Conclusion:

• The blue-black color indicates the presence of starch, which is a product of photosynthesis.
• The yellowish-brown color indicates the absence of starch.
• Since starch was only formed in the part of the leaf exposed to light, this experiment demonstrates that light is necessary for photosynthesis.