To test the presence of starch in leaves for class 7, follow these simple steps using the iodine test:

1. Take a leaf from a green plant.
2. Boil the leaf in water for a few minutes to soften it and stop any chemical reactions.
3. Immerse the boiled leaf in alcohol (ethanol) and heat it in a water bath until the leaf becomes colorless. This removes the green pigment chlorophyll.
4. Rinse the leaf with warm water to soften it.
5. Place the leaf on a white plate or tile and add a few drops of iodine solution on it.
6. Observe the color change: if the leaf turns blue-black, it indicates the presence of starch; if there is no color change, starch is absent.

This test works because iodine reacts with starch to produce a blue-black color, confirming photosynthesis has occurred in the leaf, producing starch as stored food.