Editing Respiratory system (section)

==Plants==
{{Main|Photosynthesis}}
[[Plant]]s use [[carbon dioxide]] gas in the process of [[photosynthesis]], and exhale [[oxygen]] gas as waste. The chemical equation of photosynthesis is 6 CO<sub>2</sub> (carbon dioxide) and 6 H<sub>2</sub>O (water), which in the presence of sunlight makes C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> (glucose) and 6 O<sub>2</sub> (oxygen). Photosynthesis uses electrons on the carbon atoms as the repository for the energy obtained from sunlight.<ref name=stryer>{{cite book |last1= Stryer |first1= Lubert | title=In: Biochemistry. |chapter= Photosynthesis |edition= Fourth |location= New York |publisher= W.H. FreeMan and Company|date= 1995 |pages= 653–680 |isbn= 0-7167-2009-4 }}</ref> Respiration is the opposite of photosynthesis. It reclaims the energy to power chemical reactions in cells. In so doing the carbon atoms and their electrons are combined with oxygen forming CO<sub>2</sub> which is easily removed from both the cells and the organism. Plants use both processes, photosynthesis to capture the energy and [[Aerobic cellular respiration|oxidative metabolism]] to use it.

Plant respiration is limited by the process of [[diffusion]]. Plants take in carbon dioxide through holes, known as [[stoma]]ta, that can open and close on the undersides of their [[leaf|leaves]] and sometimes other parts of their anatomy. Most plants require some oxygen for [[catabolic]] processes (break-down reactions that release energy). But the quantity of O<sub>2</sub> used per hour is small as they are not involved in activities that require high rates of [[Aerobic cellular respiration|aerobic]] metabolism. Their requirement for air, however, is very high as they need CO<sub>2</sub> for photosynthesis, which constitutes only 0.04% of the environmental air. Thus, to make 1&nbsp;g of glucose requires the removal of all the CO<sub>2</sub> from ''at least'' 18.7&nbsp;liters of air at sea level. But inefficiencies in the photosynthetic process cause considerably greater volumes of air to be used.<ref name=stryer /><ref>{{cite book|last1=Campbell|first1=Neil A.|title= Biology|edition= Second|publisher= Benjamin/Cummings Publishing Company, Inc|location= Redwood City, California|date= 1990|pages=206–223|isbn=0-8053-1800-3}}</ref>