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A potato slice shows the presence of starch with iodine solution. Where does the starch in potatoes come from? Where is the food synthesised in the plant, and how does it reach the potato?
Leaves are the primary site for photosynthesis — they are the 'food factories' of a plant.
During photosynthesis, leaves use carbon dioxide from the air, water from the soil, sunlight, and chlorophyll to produce glucose. This glucose is the immediate food product.
Glucose is then converted into starch for storage.
Transport to the potato:
The food (glucose/starch) prepared in the leaves is transported to other parts of the plant — including stems, roots, and storage organs like potatoes — through thin tube-like structures called the phloem.
The potato is an underground stem (tuber) that acts as a storage organ. The food transported through the phloem is stored in the potato in the form of starch.
When we apply iodine solution to a potato slice, it turns blue-black, confirming the presence of this stored starch.
Answer: Food (glucose) is synthesised in the leaves by photosynthesis. It is converted to starch, then transported through the phloem to the potato (an underground storage stem/tuber), where it is stored as starch — hence the blue-black iodine test result.