Photosynthesis

Animals and humans have to eat to get energy. Plants cannot do that. They make their food themselves, from ingredients they simply get from the air, the soil, and the sunlight. This process is called photosynthesis, and it is one of the most important processes on the whole planet.

The ingredients and the result

For photosynthesis the plant needs three things: carbon dioxide (CO₂ for short) from the air, water from the soil, and light from the sun. The roots take up the water, and the CO₂ flows in through tiny pores on the underside of the leaf. From these the plant builds sugar as food and releases oxygen. As a formula: 6 CO₂ + 6 H₂O + light becomes sugar + 6 O₂.

Chlorophyll catches the light

For the plant to use the light at all, it needs a special substance: chlorophyll. It sits in the leaves and makes them green. Chlorophyll captures the energy of the sunlight, and it is exactly this energy that drives photosynthesis.

The reverse of breathing

When you breathe, you take in oxygen and give off carbon dioxide. During photosynthesis the plant does exactly the opposite: it takes in carbon dioxide and gives off oxygen. This is how plants provide the oxygen that almost all living things need to breathe. Plants do breathe as well, day and night, and use up oxygen while doing so. As long as it is light, though, photosynthesis releases far more oxygen than they use up.