Similarities Between Cell Respiration & Photosynthesis
In photosynthesis, plants transform energy from sunlight, carbon dioxide and water into glucose, a sugar used to drive most cell processes. Cellular respiration transforms the energy stored in glucose into usable energy in the form of ATP -- a molecule that can transfer energy within cells -- plus carbon dioxide and water. The overall reactions for these processes are equal, but opposite, and further investigation demonstrates that they share a number of similarities.
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Energy Transformation
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Both photosynthesis and cellular respiration transform energy. Photosynthesis transforms the energy of sunlight into glucose in two phases: the light reaction and the Calvin Cycle. In cellular respiration, glucose transforms into ATP for use by the cell in two phases: glycolysis and the oxidation of pyruvic acid.
Gas Exchange
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An exchange of gasses is an inherent part of photosynthesis and cellular respiration. During photosynthesis, plants use carbon dioxide from the air and release oxygen as a result of the reaction. Other organisms, including humans, use that oxygen to drive cellular respiration, which in turn uses oxygen in the reaction to break down glucose, releasing carbon dioxide as a by-product.
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Endosymbiotic Organisms
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Chloroplasts and mitochondria are the cell organelles where portions of photosynthesis and cellular respiration, respectively, take place. Each of the organelles -- likely the remnants of simple cells ingested by more complex cells, but not digested -- provide a benefit to the other, according to endosymbiosis theory.
Chemiosmosis and Electron Transport Chains
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Electron transport chains and chemiosmosis play roles in the process by which ATP is synthesized during photosynthesis and cellular respiration. Responsible for moving electrons and protons across the membranes of the chloroplasts and mitochondria, they allow released energy to be trapped in the bonds of ATP for use in cellular processes.
Alternate Pathways
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Some plants have evolved new ways to transform light energy into glucose when conditions aren't optimal for the traditional photosynthetic process. Cellular respiration, for example, can take place without oxygen, through the alternate pathways of fermentation and anaerobic respiration.
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