The light reactions of photosynthesis (light absorption, charge separation, water splitting and electron/proton transfer) provide the reducing equivalents or ‘hydrogen’ electrons (e) and protons (H⁺) to convert carbon dioxide (CO₂) to sugars and other organic molecules that make up living organisms (biomass), including those that provide humankind with food. The same photosynthetic reactions gave rise to the fossil fuels formed millions of years ago. The burning of these organic molecules by either respiration (controlled oxidation within our bodies) or combustion of fossil fuels is the reverse to photosynthesis, releasing CO₂ and combining the ‘hydrogen’ back with oxygen to form water. In so doing, energy is released. Energy which originated from sunlight. Reproduced from Ref. [39] with permission from The Royal Society of Chemistry.