{"id":691,"date":"2017-04-16T02:54:45","date_gmt":"2017-04-16T02:54:45","guid":{"rendered":"https:\/\/pressbooks.hcfl.edu\/bio1\/chapter\/8-1-overview-of-photosynthesis\/"},"modified":"2025-08-29T18:15:18","modified_gmt":"2025-08-29T18:15:18","slug":"8-1-overview-of-photosynthesis","status":"publish","type":"chapter","link":"https:\/\/pressbooks.hcfl.edu\/bio1\/chapter\/8-1-overview-of-photosynthesis\/","title":{"raw":"Putting photosynthesis into context","rendered":"Putting photosynthesis into context"},"content":{"raw":"All living things require energy. Carbohydrates are storage molecules for energy. Living things access energy by breaking down carbohydrate molecules during the process of cellular respiration. \u00a0Plants produce carbohydrates during photosynthesis. So if plants make carbohydrate molecules during photosynthesis, do they also perform cellular respiration? The answer is yes, they do. Although energy can be stored in molecules like ATP, carbohydrates (and lipids, which can also enter cellular respiration as a source of energy) are much more stable and efficient reservoirs for chemical energy. Photosynthetic organisms also carry out the reactions of respiration to harvest the energy that they have stored in carbohydrates during photosynthesis. Plants have mitochondria in addition to chloroplasts.\n\nThe overall reaction for photosynthesis:\n
\n\n6CO2<\/sub> + 6H2<\/sub>O \u2192\u23af C6<\/sub>H12<\/sub>O6<\/sub> + 6O2<\/sub><\/strong>\n\n<\/div>\nis the reverse of the overall reaction for cellular respiration:\n
6O2<\/sub> + C6<\/sub>H12<\/sub>O6<\/sub> \u2192 6CO2<\/sub> + 6H2<\/sub>O<\/strong><\/div>\nPhotosynthesis produces oxygen as a byproduct, and respiration produces carbon dioxide as a byproduct.\u00a0In nature, there is no such thing as waste. Every single atom of matter is conserved, recycling indefinitely. Substances change form or move from one type of molecule to another, but never disappear (Figure 1<\/strong>).\n\nCO2<\/sub> is no more a form of waste produced by respiration than oxygen is a waste product of photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs energy from sunlight to build carbohydrates in the chloroplasts, and aerobic cellular respiration releases that stored energy by using oxygen to break down carbohydrates. Both organelles use electron transport chains to generate the energy necessary to drive other reactions. Photosynthesis and cellular respiration function in a biological cycle, allowing organisms to access life-sustaining energy that originates millions of miles away in a star.\n\n[caption id=\"attachment_690\" align=\"alignnone\" width=\"300\"]\"giraffe Figure 1<\/strong>\u00a0In the carbon cycle, the reactions of photosynthesis and cellular respiration share reciprocal reactants and products. (credit: modification of work by Stuart Bassil)[\/caption]\n\nThere are two basic parts of photosynthesis: the light dependent reactions and the light independent reactions (also known as the Calvin cycle).\u00a0During the light reactions, the energy from sunlight is stored in energy carrier molecules. These energy carrier molecules are then used to power the reactions of the Calvin cycle, where CO2<\/sub> molecules are joined together to produce carbohydrates such as glucose.\n\n[caption id=\"attachment_690\" align=\"alignnone\" width=\"800\"]\"\" Figure 2<\/strong> Overview of the process of photosynthesis. During the light-dependent reactions, the energy from sunlight is used by the chloroplast to create energy molecules: ATP and NADPH. These energy molecules power the Calvin cycle, which creates carbohydrates (G3P) from CO2.[\/caption]\n\n[h5p id=\"154\"]\n

References<\/h1>\nUnless otherwise noted, images on this page are licensed under CC-BY 4.0<\/a>\u00a0by\u00a0OpenStax<\/a>.\n\nText adapted from: OpenStax<\/span>, Biology. OpenStax CNX. November 11, 2017.\u00a0https:\/\/cnx.org\/contents\/GFy_h8cu@10.118:W7ctJeSI@8\/Overview-of-Photosynthesis","rendered":"

All living things require energy. Carbohydrates are storage molecules for energy. Living things access energy by breaking down carbohydrate molecules during the process of cellular respiration. \u00a0Plants produce carbohydrates during photosynthesis. So if plants make carbohydrate molecules during photosynthesis, do they also perform cellular respiration? The answer is yes, they do. Although energy can be stored in molecules like ATP, carbohydrates (and lipids, which can also enter cellular respiration as a source of energy) are much more stable and efficient reservoirs for chemical energy. Photosynthetic organisms also carry out the reactions of respiration to harvest the energy that they have stored in carbohydrates during photosynthesis. Plants have mitochondria in addition to chloroplasts.<\/p>\n

The overall reaction for photosynthesis:<\/p>\n

\n

6CO2<\/sub> + 6H2<\/sub>O \u2192\u23af C6<\/sub>H12<\/sub>O6<\/sub> + 6O2<\/sub><\/strong><\/p>\n<\/div>\n

is the reverse of the overall reaction for cellular respiration:<\/p>\n

6O2<\/sub> + C6<\/sub>H12<\/sub>O6<\/sub> \u2192 6CO2<\/sub> + 6H2<\/sub>O<\/strong><\/div>\n

Photosynthesis produces oxygen as a byproduct, and respiration produces carbon dioxide as a byproduct.\u00a0In nature, there is no such thing as waste. Every single atom of matter is conserved, recycling indefinitely. Substances change form or move from one type of molecule to another, but never disappear (Figure 1<\/strong>).<\/p>\n

CO2<\/sub> is no more a form of waste produced by respiration than oxygen is a waste product of photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs energy from sunlight to build carbohydrates in the chloroplasts, and aerobic cellular respiration releases that stored energy by using oxygen to break down carbohydrates. Both organelles use electron transport chains to generate the energy necessary to drive other reactions. Photosynthesis and cellular respiration function in a biological cycle, allowing organisms to access life-sustaining energy that originates millions of miles away in a star.<\/p>\n

\"giraffe
Figure 1<\/strong>\u00a0In the carbon cycle, the reactions of photosynthesis and cellular respiration share reciprocal reactants and products. (credit: modification of work by Stuart Bassil)<\/figcaption><\/figure>\n

There are two basic parts of photosynthesis: the light dependent reactions and the light independent reactions (also known as the Calvin cycle).\u00a0During the light reactions, the energy from sunlight is stored in energy carrier molecules. These energy carrier molecules are then used to power the reactions of the Calvin cycle, where CO2<\/sub> molecules are joined together to produce carbohydrates such as glucose.<\/p>\n

\"\"
Figure 2<\/strong> Overview of the process of photosynthesis. During the light-dependent reactions, the energy from sunlight is used by the chloroplast to create energy molecules: ATP and NADPH. These energy molecules power the Calvin cycle, which creates carbohydrates (G3P) from CO2.<\/figcaption><\/figure>\n
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