Photosynthesis
Photosynthesis is the process by which green plants capture sunlight and convert its kinetic energy into chemical energy by manufacturing complex sugar molecules or carbohydrates. The plants use carbon dioxide from the air and water as the source materials for photosynthesis. Both carbon dioxide and water store relatively small amounts of energy. The carbohydrates manufactured are rich in energy. Later, during the process of respiration, the plant breaks down these carbohydrates, and the energy that is then released is used to fuel the growth and metabolism of the plant. The photosynthetic process also releases oxygen along with the formation of the carbohydrates. The water (H2O) that is used in the photosynthetic reaction contributes its hydrogen to the formation of the carbohydrate. The oxygen that is released comes from the remaining, unused portion of the water molecule. Therefore, water is just as essential a component as carbon dioxide to the photosynthetic process. The entire reaction is carried out with the help of green, light-sensitive pigments within the plant, known as chlorophylls.
Photosynthesis is vital to the earth in two ways. It is the process by which plant life is established, thereby providing food and supporting all the other consumers in the food chain/web. The release of oxygen also ensures a livable, breathable atmosphere for all other oxygen-dependent life forms. The maintenance of a stable balance between the processes of photosynthesis (which produces oxygen) and respiration (which consumes oxygen) is critical to the environment. For example, a large amount of organic matter goes into a lake receiving sewage. This organic matter will be used as a food source by bacteria which break it down by the process of respiration just as humans do. During the respiration process, the oxygen that is dissolved in the water is used up. If there is insufficient plant material in the lake to restore this used-up oxygen by photosynthesis, the total supply of dissolved oxygen in the waters of the lake may drop dangerously. Since fish are completely dependent on the dissolved oxygen for their breathing requirements, severe drops in the concentration of dissolved oxygen may kill the fish, leading to sudden, and sometimes massive, fish kills.
Another aspect of environmental pollution are the effects on the process of photosynthesis itself. A number of contaminants have been shown to affect plant growth and metabolism by inhibiting the plant's ability to photosynthesize. Frequently, as in the case of metals like copper, lead and cadmium, the mechanism of inhibition is due to the contaminant's effect on the chlorophyll pigment. Copper replaces the necessary magnesium in the chlorophyll molecule, and the copper-substituted chlorophyll cannot effectively capture light energy. Therefore, the effectiveness of the photosynthetic process is greatly diminished, which leadsto a stunting of plant growth and a depletion of oxygen in the environment. The maintenance of a healthy level of photosynthesis is thus essential to the life of the planet, both on the global and the micro-environmental scales.
Photosynthesis. (McGraw-Hill Inc. Reproduced by permission.)Resources
Books
Weier, T. E., et al. Botany: An Introduction to Plant Biology. New York: Wiley, 1982.
Connell, D. W., and G. J. Miller. Chemistry and Ecotoxicology of Pollution. New York: Wiley, 1984.
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