Animals have to eat their food. Plants perform a small miracle instead — they make their own, building sugar out of thin air and sunlight. This process, called photosynthesis, is the reason almost every living thing on Earth can survive.
The plant's solar kitchen
Picture a leaf as a tiny solar-powered kitchen. It gathers raw ingredients, uses sunlight as the "cooker", and produces food. The cooking happens inside green structures called chloroplasts, which contain the green pigment chlorophyll — the part that actually captures the light.
The word equation
Photosynthesis takes two reactants (inputs) and makes two products (outputs):
| Substance | Role | |
|---|---|---|
| Reactant | Carbon dioxide | Gas taken IN from the air |
| Reactant | Water | Drawn up from the roots |
| Product | Glucose | The sugar (food) the plant makes |
| Product | Oxygen | Gas given OUT as waste |
Four things it needs
For the kitchen to run, four things must be present:
- Light — the energy source that powers the whole reaction.
- Carbon dioxide — the gas that supplies the carbon for the sugar.
- Water — the second raw ingredient.
- Chlorophyll — the green pigment that absorbs the light.
Take any one of these away and the kitchen shuts down. A plant kept in the dark cannot photosynthesise, no matter how much water and carbon dioxide it has, because there is no energy to drive the reaction. This is exactly why plants keep their leaves spread wide and flat — to catch as much light as possible.
Memory hook: the plant "eats light and air" — light + CO₂ + water, cooked by chlorophyll in the chloroplast, to make glucose and breathe out oxygen.