2023 · Q22
A leaf was plucked from a plant on a sunny day and kept for 2 minutes in boiling water. It was subsequently immersed in boiling alcohol and treated with iodine solution. What will be the final colour of the leaf after the test?
General KnowledgeBiology
- AColourless
- BGreen
- CBlue
- DWhite
Explanation
This is the standard starch test: boiling water kills the leaf cells, boiling alcohol removes the chlorophyll (decolourising the leaf), and iodine solution then stains any starch present. Iodine forms a blue-black complex with starch, so a leaf photosynthesizing on a sunny day turns blue, not green, colourless or white.