Introduction to Photosynthesis

Photosynthesis is the only process on Earth by which solar energy is trapped by green plants and converted into food. In precise terms, it is the synthesis of the carbohydrate glucose from the inorganic raw materials carbon dioxide and water, powered by solar energy that chlorophyll pigments capture, and it can be summarised in one overall equation:

6CO₂ + 12H₂O → (Light; Chloroplast) C₆H₁₂O₆ + 6O₂ + 6H₂O

This process is unique to green plants, and it is the final step by which light energy enters the living world — every food chain on Earth ultimately depends on it, which is why it is sometimes described as turning all life into 'bottled solar energy'. It is also one of the largest chemical processes happening on the planet: the atmosphere contains only about 0.03% carbon dioxide by volume, but that thin fraction still represents roughly 2200 billion tonnes of CO2, and the oceans hold more than 50 times as much again, dissolved as gas or locked up as carbonate. Between these two reservoirs, green plants fix around 70 billion tonnes of carbon every single year through photosynthesis.