Question

If some leaves were plucked and the iodine test was performed on them, what would be the result?

Answer 1

Hint: Iodine test is conducted to observe the presence or absence of starch content. The blue-black colour of the iodine indicates the presence of starch. Plants, through the process of photosynthesis in their leaves, produce glucose which is stored as a complex carbohydrate in the leaves.

Complete answer:
We have already discussed that the plants carry out photosynthesis to make food from raw materials available in their environment – sunlight, water, minerals – and this is stored as ‘food.’
- During photosynthesis, a plant absorbs light energy using chlorophyll in the leaves. This allows it to convert carbon dioxide and water into glucose.
- The glucose is then transported through the growing parts of the plant and transformed into cellulose, protein and oils. These are then converted into starch for further storage. Starch is a complex polysaccharide which is stored in the leaves of the plants.
- The fresh leaves were plucked and the iodine test was conducted, most of the leaf turned blue/black colour – indicating the presence of starch as the leaf was recently engaged in photosynthesis.
- If photosynthesis would not have taken place, the leaf would not turn blue/black indicating the absence of photosynthesis or no starch.

Note: Variegated leaves have green parts (presence of chlorophyll) and white parts (absence of chlorophyll). When these leaves are used for iodine tests, only the green parts later turn blue/back indicating the presence of starch. Hence, with this test it could also be concluded that chlorophyll is required for photosynthesis to occur.