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Unformatted text preview: Photosynthesis Photosynthesis is the process by which organisms that contain the pigment chlorophyll convert light energy into chemical energy which can be stored in the molecular bonds of organic molecules (e.g., sugars). Photosynthesis powers almost all trophic chains and food webs on the Earth. The net process of photosynthesis is described by the following equation: 6CO 2 + 6H 2 O + Light Energy = C 6 H 12 O 6 + 6O 2 This equation simply means that carbon dioxide from the air and water combine in the presence of sunlight to form sugars; oxygen is released as a by-product of this reaction. Light Reactions and the Calvin Cycle The process of photosynthesis is broken up into two main groups of reactions: the "light reactions" which require light energy to operate, and the "Calvin cycle" which specifically takes carbon dioxide and turns it into organic molecules. The electromagnetic energy of sunlight is converted to chemical energy in the chlorophyll-containing cells of photosynthetic organisms. In eukaryotic cells these reactions occur in the organelle known as the chloroplast . In the chloroplast, chlorophyll is the pigment that absorbs the sunlight. Chlorophyll is typically packed into stacks of membranes (called grana); it is in the grana where some of the sunlight is absorbed. Sunlight is converted to chemical energy in the form of ATP (adenosine triphosphate), which is the main energy-storing molecule in living organisms. ATP is then transported throughout the chloroplast and used to provide the chemical energy necessary to power other metabolic reactions. For example, some of the ATP is used to power the metabolic reactions in the conversion of CO 2 into sugars and other compounds. into sugars and other compounds....
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