Respiration, in which energy is released from carbohydrates for metabolic needs, takes place in plants through a process which can be expressed in a word equation as: glucose + oxygen = energy + carbon dioxide + water. The chemical equation for this process can be expressed as: C6H12O6 + 6O2 = energy + 6CO2 + 6H2O. Respiration, which is a breaking-down process that releases energy, can be viewed as the opposite of photosynthesis, which is a building-up process that takes in energy in the form of light and uses it to produce carbohydrates.
The process by which plants respire, or release energy from carbohydrates, is similar to the process that occurs in oxygen-breathing animals. Respiration in both animals and plants is also similar to oxidation, in which heat is released by burning a fuel such as wood. Although plants require carbon dioxide to produce carbohydrates through photosynthesis, they also use oxygen to perform respiration.
When oxygen is unavailable or limited, plants can release energy from stored carbohydrates through anaerobic respiration, which takes place through fermentation in plants. In its scientific sense, fermentation refers to a metabolic process that is capable of releasing energy from an organic molecule and does not require oxygen. Instead of creating the byproducts of carbon dioxide and water, the release of energy through fermentation creates the byproducts of lactic acid or ethyl alcohol, along with carbon dioxide.