The ribosomes, for instance, which manufacture proteins, rival in complexity any chemical factory. The mitochondria are power plants which extract energy from food by a complicated chain of chemical reactions involving some fifty different steps: a single cell may have up to five thousand such power plants. Then there are the centrosomes, with their spindle apparatus, which organises the incredible choreography of the cell dividing into two; and the DNA spirals of heredity, coiled up in the inner sanctum of the chromosomes, working their even more potent magic.