Water

Every living cell maintains what is called a cellular pool - the collection of molecules, both inorganic and organic, that make up its living matter. Inorganic components are water, dissolved mineral salts and free ions; organic components are carbohydrates, lipids, amino acids, proteins, nucleotides, hormones and vitamins. Some of these molecules dissolve as a true or colloidal solution in the watery intracellular fluid, while others - such as the lipids of membranes and the polysaccharides of the cell wall - exist in non-aqueous phases. The cell keeps this pool in balance by continuously taking in and eliminating specific molecules.

Minerals needed for plant growth fall into two groups by the quantity required: macronutrients (potassium, phosphorus, calcium, magnesium, sulphur, iron), needed in comparatively large amounts, and micronutrients (cobalt, zinc, boron, copper, molybdenum, manganese), needed only in trace amounts but still essential - many act as cofactors for enzymes. Manganese, for instance, is required for the enzyme that synthesises oligosaccharides and glycoproteins, while molybdenum is essential for nitrogen fixation by the enzyme nitrogenase.

Of all these components, water dominates by mass: it makes up roughly 70% of the total cellular mass in most cells, and can reach up to 95% of the mass of some plant cells, far outweighing proteins, carbohydrates, lipids, nucleic acids and ions combined.