All life on earth is dependent upon photosynthesis. Through this biogeochemical process, the planet was made habitable for terrestrial organisms. By capturing the energy of the sun, plants provide oxygen and food for themselves and other organisms. Plants are the vital link between the physical and biological world by harvesting the ultimate source of energy - sunlight.
"When a particle of light strikes a molecule of chlorophyll, an electron is jolted out of the molecule and raised to a higher energy level. Within a fraction of a second, it returns to its previous energy state. All life on this planet is dependent upon the energy momentarily gained by the electron. The process by which some of the energy given up by the electron in returning to its original energy level is converted into chemical energy - energy in a form usable by living systems - is known as photosynthesis." (Raven & Curtis, 1981)
The chlorophyll molecule is stored in plant cells within the organelles called chloroplasts. In the chloroplasts, photosynthesis occurs in two stages. In the first stage, energy in sunlight is captured, water is split, and oxygen is freed into the atmosphere. In the second stage, the energy captured helps to 'fix' carbon from carbon dioxide to produce sugars. These sugars will ultimately provide food for the plant, which is then available to animals either directly (by herbivores and omnivores that eat the plants) or indirectly (by carnivores and omnivores that eat the herbivores).
Our food, clothing, shelter, and energy are all rooted in photosynthesis.
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