Photosynthesis: turning light into stored chemical energy — Biology, 14–17 years
Photosynthesis explains how plants, algae and some bacteria use light to make glucose from carbon dioxide and water. It links sunlight, food and the oxygen in the air.
What photosynthesis does
A green plant captures light energy in chloroplasts and uses it to join carbon dioxide with water, making glucose. Oxygen is released as a by-product. The glucose can be used immediately or built into starch and other substances.
Why photosynthesis matters
An ecosystem needs a way to bring energy from the Sun into living matter. Photosynthesis solves that problem by storing light energy in glucose, which plants and other organisms can use. It also supplies much of the oxygen needed for aerobic respiration.
Worked example: following the atoms
Start with six carbon dioxide molecules and six water molecules. Light energy drives the plant to rearrange their atoms into one glucose molecule, C₆H₁₂O₆, and six oxygen molecules, O₂. No carbon vanishes: it moves from carbon dioxide into glucose.
Trap: plants do not get food from soil
It is reasonable to think soil is plant food because roots absorb water and mineral ions from it, and fertiliser helps plants grow. But most of a plant’s dry mass comes from carbon dioxide in the air, changed into organic molecules by photosynthesis. Soil supplies materials, not the main energy source.
Where photosynthesis appears
Photosynthesis shapes farming, forestry and climate discussions. Crop yield depends partly on how much light, water and carbon dioxide leaves can use, while forests store carbon in wood and soil. Algae also photosynthesise in oceans and contribute substantially to global oxygen production.
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