Photosynthesis

Photosynthesis is an energetic biochemical reaction that takes place inside plants.

Role of photosynthesis

The purpose of photosynthesis is to create energy (in the form of carbohydrates) from luminous energy produced by the sun. Organisms that use the mechanism of photosynthesis are autotrophic, because they produce organic matter from inorganic matter.

Mechanism of photosynthesis

Solar energy is used to oxidise water and reduce carbon dioxide in order to synthesise organic substances (carbohydrates). This phenomenon takes place in chloroplasts, an organelle specific to plants, around the thylakoid membranes where photosystems I and II and cytochromes are located.

Energy produced by photosynthesis

It takes six molecules of carbon dioxide and six molecules of water to synthesise one molecule of glucose, releasing six molecules of dioxygen, with the help of luminous energy.

6 CO₂ + 6 H₂O + luminous energy → C₆H₁₂O₆ (glucose) + 6 O₂

This process of production is broken down into two successive steps:

• photochemical reactions (light phase) : 12 H₂O + light → 6 O₂ + chemical energy (24 H) ;
• Calvin cycle (dark phase) : 6 CO₂ + chemical energy (24 H) → C₆H₁₂O₆ + 6 H₂O.