Published online by Cambridge University Press: 17 December 2021
Notwithstanding the seemingly large choice available, only about a couple of dozen elements appear to be consistently used to construct and operate the enormous diversity of biological organisms that still exist on our planet today. Indeed one is drawn to the ineluctable conclusion that all life on Earth must have a common origin, if only for the fact that just six elements (hydrogen, carbon, nitrogen, oxygen, phosphorus, and calcium) make up almost 99% of the mass of all living cells of both animals and plants. But many other elements account for the remainder. In terms of biochemistry, all these elements are the basis of four main classes of molecules: carbohydrates, lipids, proteins, and nucleic acids. Thus the majority of organisms all require the same essential elements, although there are nevertheless some interesting differences among them. Hence it seems that all animals require sodium, but some plants do not.
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