Structures Associated with Catabolism

Abstract

Living systems are mainly composed of only twenty-two of the hundred or so naturally occurring elements; it would seem that during evolution these elements have been selected because of their particular suitability for maintaining the living process. Most of the elements essential for life are relatively rare in the lithosphere and because metabolic events in the biosphere occur on such a massive scale—photosynthesis by all photosynthetic organisms fixes around 50 × 10⁹ tons of carbon a year—it is essential that these elements be recycled in order to allow biological activity to continue at its present rate for any prolonged period of time. Calculations suggest that without recycling all the carbon dioxide present in the lithosphere would be removed in three hundred years, the concentration of oxygen in the atmosphere would be doubled in two thousand years and all the waters of the ocean decomposed in two million years. Yet we know the gaseous composition of the atmosphere is relatively stable, although recent industrial activities of mankind have caused small changes, thus it follows that the combined activities of biological processes must return materials to the lithosphere as rapidly as they are able to remove them from it. This steady state is maintained by the carefully controlled balance of synthetic (anabolic) and degradational (catabolic) metabolic processes.