Photosynthesis

Several examples of photochemical processes were listed at the beginning of this discussion. Here we will look at these in greater detail.

As was mentioned previously, photochemical processes result from the absorption of ultraviolet and visible radiation by molecules and the consequent reaction of the electronically-excited molecules. Probably the most important example of a photochemical process is photosynthesis, the conversion of carbon dioxide and water to glucose and oxygen, which is catalyzed by the chlorophyll in green plants.

The reaction requires the input of energy, which for photosynthesis, comes from sunlight, which contains the entire electromagnetic spectrum. The overall reaction for photosynthesis can be written as

A chlorophyll molecule absorbs energy from the visible portion of the electromagnetic radiation coming from sunlight. The absorbed radiation increases the energy of an electron in an outer orbital of the chlorophyll molecule and places the chlorophyll molecule into an excited or higher-energy state. This excited state molecule of chlorophyll then begins a complex series of biochemical reactions that result in the formation of glucose and oxygen.

A photosynthesis diagram.

The food that we eat, the oxygen that we breathe, and the coal and oil that is used in the petrochemical and energy industries are all products of photosynthesis. It should be obvious that photosynthesis is essential for life on this planet.

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