Question

On adding iodine to a leaf boiled in alcohol, a blue-black colour appears. This means that

• A. Starch is produced in the leaf
• B. Starch is not produced in the leaf
• C. Glucose is produced in the leaf
• D. Glucose is not produced in the leaf

Answer 1

The correct option is A Starch is produced in the leaf

The iodine test is used to test for the presence of starch.
When treated with iodine solution, iodine forms a complex with starch that produces an intense blue-black colour. This indicates that starch was produced in the leaves. If there has been no starch produced, then the leaves would appear bleached or colourless.
Iodine does not react with glucose or other molecules producing coloured products. Therefore presence of other substances cannot detected by iodine test.