What is the difference between photosynthesis and respiration?

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gsenviro eNotes educator| Certified Educator

There are a number of differences between the processes of photosynthesis and respiration.

Photosynthesis takes place in green plants, cyanobacteria, and algae. In this process, carbon dioxide and water, in the presence of sunlight, are converted to glucose and oxygen. In other words, the process causes the conversion of light energy to chemical energy. Since the energy is stored in the form of glucose molecules in photosynthesis, this process can be considered to be endothermic in nature. Photosynthesis can be summarized by the following chemical reaction:

`6CO_2 + 6H_2O + sunlight -> C_6H_12O_6 + 6O_2`

Respiration, on the other hand, takes place in all living organisms. This process can be considered to be the "reverse" of photosynthesis, since the reactants in this process are glucose and oxygen, while the products are carbon dioxide and water. Since energy is released in this process (in the form of ATP molecules), this process is exothermic. The process of respiration can be summarized by the following chemical reaction:

`C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O + ATP`

(Here, ATP simply refers to the energy that is released during the process of respiration. The actual number of ATP molecules released during respiration will be dependent on a number of factors, including presence or absence of oxygen, etc.)

Also note that while photosynthesis takes place only in the presence of sunlight, the process of respiration takes place continuously throughout the lifetime of living organisms. 

Hope this helps.

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