Photosynthesis
Photosynthesis is the process by which plants, algae and some bacteria store energy from the sun in the form of
carbohydrates. These carbohydrates act as fuels: they are either used by the plant, or eaten by plant-eating animals, or,
after an organism has died, converted at high temperatures and pressures underground into fossil fuels. Photosynthesis
is thus the ultimate source of all fuel we use today. Photosynthesis uses water and carbon dioxide as raw materials and
oxygen is released as a waste product. It is thus also thanks to photosynthesis that we have the oxygen that we breathe.
Photosynthesis can be divided into four steps:
1. light harvesting
2. charge separation
3. water splitting
4. fuel production
Light harvesting is the absorption and ‘concentration’ of sunlight. The collected light energy is then funnelled to the
place where charge separation takes place (the so-called ‘reaction centre’). There, the energy from the sunlight is used
to separate positive and negative charges from each other. The positive charges are used to split water into hydrogen
and oxygen (step 3). The negative charges are used to produce the carbohydrate fuel from carbon dioxide (step 4).