The Process of Photosynthesis The Light Reactions

Abstract

The oxidation of foodstuffs to carbon dioxide and water provides the energy required by all aerobic cells to maintain their state of life and to grow. Energy stored in these foodstuffs is lost irreversibly as heat as the work of life is performed. But since the foodstuffs themselves were once parts of living cells, eventually all living matter reverts to carbon dioxide, water, and ammonia or free nitrogen. To prevent life from consuming itself, the energy-bearing compounds must be regenerated, which requires an input of external energy at least equal to that lost as heat. The only source of readily available external energy for living systems on earth is the sun. Given the appropriate mechanisms for performing the process, light energy can be converted to electrical or chemical energy. However, cells in the animal kingdom do not have this capacity. Plant cells, on the other hand, because they contain photosynthetic structures, can accomplish this feat. Chlorophyll-bearing cells are the primary* sector of the earth’s population that are capable of production, in this sense, and they alone enable all cells in the animal kingdom to exist. Green plant cells can synthesize their fabric de novo from carbon dioxide, water, and other inorganic compounds. Thus, they are autotrophic (self-fed, requiring no organic matter for growth), whereas all other cells are heterotrophic (fed by others, requiring preformed organic matter for growth]. Plant cells accumulate energy, whereas others dissipate it. The synthesis of carbohydrates from carbon dioxide and water, with the aid of sunlight, is without doubt the most fundamental of all biological activities.