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Activity 5.1 — Starch Test (Iodine Test)
NCERT Activity 5.1: Test a leaf for starch using the iodine test. Boil in water, decolorize in alcohol, rinse, then add iodine — the leaf turns blue-black if starch is present.
How To Perform
1
Boil Leaf in Water
Kill the leaf cells and make them permeable.
2
Boil Leaf in Alcohol
Remove chlorophyll to decolorize the leaf (use a water bath!).
3
Rinse in Cold Water
Soften the leaf and remove alcohol residue.
4
Add Iodine Solution
Observe the colour change on the decolorized leaf.
5
Conclude
Blue-black colour confirms starch → photosynthesis occurred.
⚠️ Safety Notes
- •Alcohol (methylated spirit) is highly flammable. NEVER heat it directly over a flame — always use a water bath.
- •Handle boiling water and hot beakers with care. Use tongs or a holder.
- •Wear safety goggles when handling alcohol and iodine solution.