Glucose combustion. Glucose being burnt on a spoon to produce a flame (centre) with a steam plume escaping (left). The reaction of the glucose (a sugar, C6.H12.O6) with the oxygen (O2) in the air, produces carbon dioxide (CO2) and water (H2O). If combustion is incomplete (as indicated by the yellow colour of the flame, then burnt carbon (soot, black) is also produced. The controlled reaction of glucose with oxygen in body cells, via a complicated biochemical reaction, provides energy in a similar way to the energy being liberated here.