In inorganic systems, such a reaction as burning sugar would need much more heat. The fluid that mediates both food and gas exchange is, of course, blood, which itself contains cells that respire in exactly the same manner as all the other types of cells. In the higher animals, the colonies of cells comprising the individual are interdependent. Although some may be kept alive individually in Petri dishes, none has a free, independent existence any more, except briefly, at conception. When we stop to consider how an organism, commencing with that single cell resulting from the fusion of parental sperm and egg, can go on to differentiate into the staggering numbers of different tissue types, we cannot but be astonished at the extraordinary complexity involved.
Some cells proceed to make proteins employing iron atoms to carry oxygen.
Others use calcium to help construct bones and teeth, or sulphur to make hair, horn or hooves. Nerve and muscle cells engage ions from the salts of sodium, potassium and calcium in order to generate the electrical charges needed to make movement of muscles, indeed, even the movement of ideas, from cell to cell. The staggering diversity of chemical reactions that occur in different tissues of differing species is simply beyond comprehension. Yet there are common rules. Many of the fundamental laws of physics and chemistry apply equally to living and non living things.