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UPSC Prelims 1986 · Environment · Nature’s Machinery
The final product of photosynthesis is
- (a) Carbohydrates
- (b) Carbon dioxide
- (c) Oxygen
- (d) Water
Show the answer and explanation
Answer: (a) Carbohydrates
Photosynthesis makes glucose (a carbohydrate), stored as starch.
The idea
Photosynthesis exists to make food for the plant. It uses light energy to join carbon dioxide and water into sugar. Oxygen is what is left over when water is split, and the plant releases it as waste.
CO₂ + H₂O → sunlight + chlorophyll → glucose (C₆H₁₂O₆) → + O₂ released
Why the others are wrong
(b) CO₂ is a raw material, not a product.
(c) Oxygen is released, but as a by-product of splitting water.
(d) Water is a raw material.
The trap
Oxygen is what we care about, so it feels like the “product”. For the plant, the product is sugar.
Also know
The sugar is then stored as starch, built into cellulose for cell walls, or moved around the plant as sucrose. Experiments with labelled oxygen showed that the oxygen released comes from water, not from carbon dioxide.
🔒 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Final product = carbohydrate; O₂ = by-product.
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