Explain photosynthesis simply

Everyone knows 'plants make food from sunlight'. What is actually happening inside a leaf during photosynthesis?

Think of a leaf as a solar-powered kitchen. The solar panels are chlorophyll molecules in chloroplasts; the raw ingredients are water (up from the roots) and carbon dioxide (in through pores called stomata); the product is glucose — the plant's food and building material. Oxygen leaves as a by-product, which is lucky for us.

It runs in two stages: first capture the energy (needs light), then use that energy to build sugar (doesn't need light directly).

Overall equation: 6CO₂ + 6H₂O —(light, chlorophyll)→ C₆H₁₂O₆ + 6O₂.

Light reactions (thylakoid membranes): chlorophyll absorbs light, water is split (photolysis — the source of the released O₂), and the energy is banked as ATP and NADPH.

Calvin cycle (stroma): the ATP and NADPH power the fixation of CO₂ into glucose. It's light-independent but runs mainly in daylight, because it constantly consumes the light reactions' products.

Classic experiment: keep a destarched potted plant in sunlight with one leaf partly covered by black paper. After a day, test that leaf with iodine — the exposed area turns blue-black (starch present), the covered area doesn't. Light was the missing ingredient: no light, no photosynthesis, no starch.

• Saying the released oxygen comes from CO₂ — isotope-tracing experiments show it comes from the splitting of water.
• Calling the Calvin cycle the 'dark reactions' as if it happens at night; it merely doesn't use light directly, and it stalls without the light reactions feeding it.
• Forgetting plants respire too — they burn glucose for energy day and night, just like us; photosynthesis runs alongside respiration, not instead of it.

• NCERT Class 11 Biology, Ch. 11 — Photosynthesis in Higher Plants
• Khan Academy — Photosynthesis