The whole cycle of chemical changes which is involved in plant growth represents the net result of two opposite processes; the first of these is a constructive one which has at least three different phases: namely, a synthesis of complex organic compounds, the translocation of this synthetized material to the centers of growth, and the building up of this food material into tissues or reserve supplies; and the second is a destructive process of respiration whereby carbohydrate material is broken down, potential energy is released, and carbon dioxide is excreted.
The synthetic processes which take place in plants are of two types; namely, photosynthesis, in which sugars are produced, and another, which has no specific name, whereby proteins are elaborated. The translocation of the synthetized material involves the change of insoluble compounds into soluble ones, effected by the aid of enzymes. For storage purposes, the soluble forms are usually, though not always, condensed again into more complex forms, these latter changes requiring much less energy than do the original syntheses from raw materials.