The oxidation of glucose, which provides the energy to power all animals looks precisely like photosynthesis in reverse:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
It appears that life simply plucks carbon out of the air, transforming it through the alchemy of photosynthesis into the universal food available for all and sundry to feast on. But things are far more interesting than that, because although plants and algae are busy making D-glucose from carbon dioxide, water and sunlight, very little of it stay in this immediately useful form for long. Instead, plants use the sugars to build much longer-chain molecules, including the structural molecules cellulose and lignin. Cellulose is a long chain of D-glucose molecules known as a polysaccharide, with the general chemical formula (C6H12O5)n. The n means that a very large number of these units are linked together. Here is carbon functioning as scaffolding, bonding to other carbon atoms over and over again to form a giant organic molecule. Cellulose chains can be over 10,000 units long. Cellulose is the most common organic compound on Earth, forming the structure of the cell walls in green plants. It is strong and stable, and therefore difficult to break down.
1. Brian Cox, the wonders of life, page 295