How Are Photosynthesis & Cellular Respiration Related?

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Photosynthesis and cellular respiration are complementary biochemical reactions. Photosynthesis requires the products of respiration, while respiration requires the products of photosynthesis. Together these reactions allow cells to make and store energy and help regulate atmospheric concentrations of carbon dioxide and oxygen.


Only autotrophic organisms like plants, algae and some bacteria can perform photosynthesis, while most organisms perform respiration. Autotrophic organisms perform both photosynthesis and respiration.


During photosynthesis light energy from the sun causes carbon dioxide and water to be transformed into glucose (sugar) and oxygen. (See reference 2 page 107)

Cellular Respiration

Respiration requires glucose and oxygen to make carbon dioxide and water. In the process, chemical energy in the form of adenosine triphosphate (ATP) is released.


ATP is the form of chemical energy all cells require to perform the functions necessary to life.

Photosynthesis releases oxygen into the atmosphere and absorbs carbon dioxide. Respiration requires oxygen to allow cells to make ATP.


Respiration can also occur in yeast or bacteria in the absence of oxygen, and this process is called fermentation. Fermentation is the process that produces beer, wine, yogurt, soy sauce and other food products.

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