You have photosynthesis to thank for every lungful of air you breathe. In fact, photosynthesis is probably the most important biochemical process on the planet. Besides pumping oxygen into the atmosphere, it is the energy source behind all our food and almost all the heat and power we use. Without it, the evolution of life on Earth would have followed a very different path. Yet unpicking the molecular details of photosynthetic chemistry, and understanding how the process shapes our environment, remains a key challenge
Photosynthesis: the basics
Photosynthesis is the process by which plants, algae and some bacteria convert carbon dioxide and water into carbohydrates using energy from sunlight. In most cases, they achieve this by splitting apart the hydrogen and oxygen in water (H2O), giving off oxygen (O2) as a by-product. In many ways, photosynthesis is the reverse of respiration: when we animals respire, we use O2 to burn up carbohydrates, releasing CO2 and producing the energy we need to live.
Photosynthesis consists of a complex series of reactions, but it can be divided into four key stages: light absorption, charge separation, carbon fixation and oxygen evolution. First, a photon of sunlight is absorbed by chlorophyll pigments and passed to a “reaction centre”, which contains a specially aligned pair of chlorophyll molecules. Here charge separation occurs: the chlorophyll pair uses the photon’s energy to spit out an electron. This triggers the final two stages. The ejected electron is …
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