{"id":693,"date":"2018-05-03T18:05:26","date_gmt":"2018-05-03T18:05:26","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/using-light-energy-to-make-organic-molecules\/"},"modified":"2018-06-27T17:53:45","modified_gmt":"2018-06-27T17:53:45","slug":"using-light-energy-to-make-organic-molecules","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/using-light-energy-to-make-organic-molecules\/","title":{"raw":"Using Light Energy to Make Organic Molecules","rendered":"Using Light Energy to Make Organic Molecules"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>Describe the Calvin cycle<\/li>\r\n \t<li>Define carbon fixation<\/li>\r\n \t<li>Explain how photosynthesis works in the energy cycle of all living organisms<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp47951280\">After the energy from the sun is converted into chemical energy and temporarily stored in ATP and NADPH molecules, the cell has the fuel needed to build carbohydrate molecules for long-term energy storage. The products of the light-dependent reactions, ATP and NADPH, have lifespans in the range of millionths of seconds, whereas the products of the light-independent reactions (carbohydrates and other forms of reduced carbon) can survive almost indefinitely. The carbohydrate molecules made will have a backbone of carbon atoms. But where does the carbon come from? It comes from carbon dioxide\u2014the gas that is a waste product of respiration in microbes, fungi, plants, and animals.<\/p>\r\n\r\n<div id=\"fs-idm160767200\" class=\"bc-section section\">\r\n<h3>The Calvin Cycle<\/h3>\r\n<p id=\"fs-idm22256\">In plants, carbon dioxide (CO<sub>2<\/sub>) enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells. Once in the mesophyll cells, CO<sub>2<\/sub> diffuses into the stroma of the chloroplast\u2014the site of light-independent reactions of photosynthesis. These reactions actually have several names associated with them. Another term, the Calvin cycle, is named for the man who discovered it, and because these reactions function as a cycle. Others call it the Calvin-Benson cycle to include the name of another scientist involved in its discovery. The most outdated name is \u201cdark reaction,\u201d because light is not directly required (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_01\">(Figure)<\/a>). However, the term dark reaction can be misleading because it implies incorrectly that the reaction only occurs at night or is independent of light, which is why most scientists and instructors no longer use it.<\/p>\r\n\r\n<div id=\"fig-ch08_03_01\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"650\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180513\/Figure_08_03_01.png\" alt=\"This illustration shows that ATP and NADPH produced in the light reactions are used in the Calvin cycle to make sugar.\" width=\"650\" height=\"1197\" \/> <strong>Figure 1. <\/strong>Light reactions harness energy from the sun to produce chemical bonds, ATP, and NADPH. These energy-carrying molecules are made in the stroma where carbon fixation takes place.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-idp23499712\">The light-independent reactions of the Calvin cycle can be organized into three basic stages: <em>fixation, reduction, and regeneration.<\/em><\/p>\r\n\r\n<div id=\"fs-idm53150960\" class=\"bc-section section\">\r\n<h4>Stage 1: Fixation<\/h4>\r\n<p id=\"fs-idm187183792\">In the stroma, in addition to CO<sub>2<\/sub>, two other components are present to initiate the light-independent reactions: an enzyme called ribulose-1,5-bisphosphate carboxylase\/oxygenase (RuBisCO), and three molecules of ribulose bisphosphate (RuBP), as shown in <a class=\"autogenerated-content\" href=\"#fig-ch08_03_02\">(Figure)<\/a>. RuBP has five atoms of carbon, flanked by two phosphates.<\/p>\r\n\r\n<div id=\"fs-idp117078128\" class=\"art-connection textbox examples\">\r\n<h3>Art Connection<\/h3>\r\n<div id=\"fig-ch08_03_02\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"350\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180518\/Figure_08_03_02.png\" alt=\"A diagram of the Calvin cycle is shown with its three stages: carbon fixation, 3-PGA reduction, and regeneration of RuBP. In stage 1, the enzyme RuBisCO adds a carbon dioxide to the five-carbon molecule RuBP, producing two three-carbon 3-PGA molecules. In stage 2, two NADPH and two ATP are used to reduce 3-PGA to GA3P. In stage 3 RuBP is regenerated from GA3P. One ATP is used in the process. Three complete cycles produces one new GA3P, which is shunted out of the cycle and made into glucose (C6H12O6).\" width=\"350\" height=\"1345\" \/> <strong>Figure 2. <\/strong>The Calvin cycle has three stages. In stage 1, the enzyme RuBisCO incorporates carbon dioxide into an organic molecule, 3-PGA. In stage 2, the organic molecule is reduced using electrons supplied by NADPH. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue. Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-idp27000112\">Which of the following statements is true?<\/p>\r\n\r\n<ol id=\"fs-idm188800912\" type=\"a\">\r\n \t<li>In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. GA3P and water are products.<\/li>\r\n \t<li>In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. GA3P and oxygen are products.<\/li>\r\n \t<li>In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products.<\/li>\r\n \t<li>In photosynthesis, water and carbon dioxide are reactants. GA3P and oxygen are products.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"133952\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"133952\"]\r\n\r\nD[\/hidden-answer]\r\n\r\n<\/div>\r\n<p id=\"fs-idm152383840\">RuBisCO catalyzes a reaction between CO<sub>2<\/sub> and RuBP. For each CO<sub>2<\/sub> molecule that reacts with one RuBP, two molecules of another compound 3-phospho glyceric acid (3-PGA) form. PGA has three carbons and one phosphate. Each turn of the cycle involves only one RuBP and one carbon dioxide and forms two molecules of 3-PGA. The number of carbon atoms remains the same, as the atoms move to form new bonds during the reactions (3 C atoms from 3CO<sub>2<\/sub> + 15 C atoms from 3RuBP = 18 C atoms in 6 molecules of 3-PGA). This process is called carbon fixation, because CO<sub>2<\/sub> is \u201cfixed\u201d from an inorganic form into organic molecules.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm89996944\" class=\"bc-section section\">\r\n<h4>Stage 2: Reduction<\/h4>\r\n<p id=\"fs-idm86368800\">ATP and NADPH are used to convert the six molecules of 3-PGA into six molecules of a chemical called glyceraldehyde 3-phosphate (G3P). That is a reduction reaction because it involves the gain of electrons by 3-PGA. (Recall that a reduction is the gain of an electron by an atom or molecule.) Six molecules of both ATP and NADPH are used. For ATP, energy is released with the loss of the terminal phosphate atom, converting it into ADP; for NADPH, both energy and a hydrogen atom are lost, converting it into NADP<sup>+<\/sup>. Both of these molecules return to the nearby light-dependent reactions to be reused and re-energized.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm23606256\" class=\"bc-section section\">\r\n<h4>Stage 3: Regeneration<\/h4>\r\n<p id=\"fs-idm57998960\">Interestingly, at this point, only one of the G3P molecules leaves the Calvin cycle and is sent to the cytoplasm to contribute to the formation of other compounds needed by the plant. Because the G3P exported from the chloroplast has three carbon atoms, it takes three \u201cturns\u201d of the Calvin cycle to fix enough net carbon to export one G3P. But each turn makes two G3Ps, thus three turns make six G3Ps. One is exported while the remaining five G3P molecules remain in the cycle and are used to regenerate RuBP, which enables the system to prepare for more CO<sub>2<\/sub> to be fixed. Three more molecules of ATP are used in these regeneration reactions.<\/p>\r\n\r\n<div id=\"fs-idm132001936\" class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-idm125936400\">This <a href=\"http:\/\/openstaxcollege.org\/l\/calvin_cycle\" target=\"_window\">link<\/a> leads to an animation of the Calvin cycle. Click stage 1, stage 2, and then stage 3 to see G3P and ATP regenerate to form RuBP.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm158415504\" class=\"evolution textbox examples\">\r\n<h3>Evolution Connection<\/h3>\r\n<p id=\"fs-idm104644592\"><strong>Photosynthesis<\/strong><\/p>\r\nDuring the evolution of photosynthesis, a major shift occurred from the bacterial type of photosynthesis that involves only one photosystem and is typically anoxygenic (does not generate oxygen) into modern oxygenic (does generate oxygen) photosynthesis, employing two photosystems. This modern oxygenic photosynthesis is used by many organisms\u2014from giant tropical leaves in the rainforest to tiny cyanobacterial cells\u2014and the process and components of this photosynthesis remain largely the same. Photosystems absorb light and use electron transport chains to convert energy into the chemical energy of ATP and NADH. The subsequent light-independent reactions then assemble carbohydrate molecules with this energy.\r\n<p id=\"fs-idm140187264\">In the harsh dry heat of the desert, plants must conserve every drop of water must be used to survive. Because stomata must open to allow for the uptake of CO<sub>2<\/sub>, water escapes from the leaf during active photosynthesis. Desert plants have evolved processes to conserve water and deal with harsh conditions. Mechanisms to capture and store CO<sub>2<\/sub> allows plants to adapt to living with less water. Some plants such as cacti (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_03\">(Figure)<\/a>) can prepare materials for photosynthesis during the night by a temporary carbon fixation\/storage process, because opening the stomata at this time conserves water due to cooler temperatures. During the day cacti use the captured CO<sub>2<\/sub> for photosynthesis, and keep their stomata closed.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fig-ch08_03_03\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"255\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180521\/Figure_08_03_03.jpg\" alt=\"This photo shows short, round prickly cacti growing in cracks in a rock.\" width=\"255\" height=\"714\" \/> <strong>Figure 3. <\/strong>The harsh conditions of the desert have led plants like these cacti to evolve variations of the light-independent reactions of photosynthesis. These variations increase the efficiency of water usage, helping to conserve water and energy. (credit: Piotr Wojtkowski)[\/caption]\r\n\r\n<\/div>\r\n<div class=\"wp-caption-text\"><\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm121372848\" class=\"bc-section section\">\r\n<h3>The Energy Cycle<\/h3>\r\n<p id=\"fs-idm186246928\">Whether the organism is a bacterium, plant, or animal, all living things access energy by breaking down carbohydrate and other carbon-rich organic molecules. But if plants make carbohydrate molecules, why would they need to break them down, especially when it has been shown that the gas organisms release as a \u201cwaste product\u201d (CO<sub>2<\/sub>) acts as a substrate for the formation of more food in photosynthesis? Remember, living things need energy to perform life functions. In addition, an organism can either make its own food or eat another organism\u2014either way, the food still needs to be broken down. Finally, in the process of breaking down food, called cellular respiration, heterotrophs release needed energy and produce \u201cwaste\u201d in the form of CO<sub>2<\/sub> gas.<\/p>\r\n<p id=\"fs-idm154538240\">However, in nature, there is no such thing as \u201cwaste.\u201d Every single atom of matter and energy is conserved, recycled over and over infinitely. Substances change form or move from one type of molecule to another, but their constituent atoms never disappear (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_04\">(Figure)<\/a>).<\/p>\r\n<p id=\"fs-idp23524720\">In reality, CO<sub>2<\/sub> is no more a form of waste than oxygen is wasteful to photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs light energy to build carbohydrates\r\nin chloroplasts, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates in the cytoplasm and mitochondria. Both processes use electron transport chains to capture the energy necessary to drive other reactions. These two powerhouse processes, photosynthesis and cellular respiration, function in biological, cyclical harmony to allow organisms to access life-sustaining energy that originates millions of miles away in a burning star humans call the sun.<\/p>\r\n\r\n<div id=\"fig-ch08_03_04\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"420\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180524\/Figure_08_03_05.jpg\" alt=\"This photograph shows a giraffe eating leaves from a tree. Labels indicate that the giraffe consumes oxygen and releases carbon dioxide, whereas the tree consumes carbon dioxide and releases oxygen.\" width=\"420\" height=\"667\" \/> <strong>Figure 4. <\/strong>Photosynthesis consumes carbon dioxide and produces oxygen. Aerobic respiration consumes oxygen and produces carbon dioxide. These two processes play an important role in the carbon cycle. (credit: modification of work by Stuart Bassil)[\/caption]\r\n\r\n<\/div>\r\n<div class=\"wp-caption-text\"><\/div>\r\n<\/div>\r\n<div id=\"fs-idp98484032\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-idm142625264\">Using the energy carriers formed in the first steps of photosynthesis, the light-independent reactions, or the Calvin cycle, take in CO<sub>2<\/sub> from the atmosphere. An enzyme, RuBisCO, catalyzes a reaction with CO<sub>2<\/sub> and another organic compound, RuBP. After three cycles, a three-carbon molecule of G3P leaves the cycle to become part of a carbohydrate molecule. The remaining G3P molecules stay in the cycle to be regenerated into RuBP, which is then ready to react with more CO<sub>2<\/sub>. Photosynthesis forms an energy cycle with the process of cellular respiration. Because plants contain both chloroplasts and mitochondria, they rely upon both photosynthesis and respiration for their ability to function in both the light and dark, and to be able to interconvert essential metabolites.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idm98385648\" class=\"art-exercise\">\r\n<h3>Art Connections<\/h3>\r\n<div id=\"fs-idm60512080\">\r\n<div id=\"fs-idm185942880\">\r\n<p id=\"fs-idp5541104\"><a class=\"autogenerated-content\" href=\"#fig-ch08_03_02\">(Figure)<\/a> Which of the following statements is true?<\/p>\r\n\r\n<ol id=\"fs-idm70810960\" type=\"a\">\r\n \t<li>In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. G3P and water are products.<\/li>\r\n \t<li>In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. G3P and oxygen are products.<\/li>\r\n \t<li>In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products.<\/li>\r\n \t<li>In photosynthesis, water and carbon dioxide are reactants. G3P and oxygen are products.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"fs-idp63246768\">\r\n<p id=\"fs-idm58178944\">[reveal-answer q=\"456097\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"456097\"]<\/p>\r\n<a href=\"#fig-ch08_03_02\">(Figure)<\/a> D[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm62125584\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-idm107405520\">\r\n<div id=\"fs-idm48699104\">\r\n<p id=\"fs-idm36712624\">Which molecule must enter the Calvin cycle continually for the light-independent reactions to take place?<\/p>\r\n\r\n<ol id=\"fs-idm152508560\" type=\"a\">\r\n \t<li>RuBisCO<\/li>\r\n \t<li>RuBP<\/li>\r\n \t<li>3-PGA<\/li>\r\n \t<li>CO<sub>2<\/sub><\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"fs-idm47070176\">\r\n<p id=\"fs-idp2247264\">[reveal-answer q=\"941992\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"941992\"]D[\/hidden-answer]<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp62052848\">\r\n<div id=\"fs-idm147194688\">\r\n<p id=\"fs-idm186510704\">Which order of molecular conversions is correct for the Calvin cycle?<\/p>\r\n\r\n<ol id=\"fs-idm164585152\" type=\"a\">\r\n \t<li>[latex]\\text{RuBP\u00a0+\u00a0G3P\u00a0}\\to \\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0sugar}[\/latex]<\/li>\r\n \t<li>[latex]\\text{RuBisCO\u00a0}\\to {\\text{\u00a0CO}}_{2}\\text{\u00a0}\\to \\text{\u00a0RuBP\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\r\n \t<li>[latex]{\\text{RuBP\u00a0+\u00a0CO}}_{2}\\text{\u00a0}\\to \\text{\u00a0}\\left[\\text{RuBisCO}\\right]\\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\r\n \t<li>[latex]{\\text{CO}}_{2}\\text{\u00a0}\\to \\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0RuBP\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"fs-idm190120016\">\r\n<p id=\"fs-idm73937824\">[reveal-answer q=\"859746\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"859746\"]<\/p>\r\nC[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm99331456\">\r\n<div id=\"fs-idm99331200\">\r\n<p id=\"fs-idm24937568\">Where in eukaryotic cells does the Calvin cycle take place?<\/p>\r\n\r\n<ol id=\"fs-idm24937184\" type=\"a\">\r\n \t<li>thylakoid membrane<\/li>\r\n \t<li>thylakoid lumen<\/li>\r\n \t<li>chloroplast stroma<\/li>\r\n \t<li>granum<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"fs-idp62251696\">\r\n<p id=\"fs-idm152471856\">[reveal-answer q=\"654887\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"654887\"]<\/p>\r\nC[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm55613456\">\r\n<div id=\"fs-idm55613200\">\r\n<p id=\"fs-idp90133632\">Which statement correctly describes carbon fixation?<\/p>\r\n\r\n<ol id=\"fs-idp90134016\" type=\"a\">\r\n \t<li>the conversion of CO<sub>2<\/sub> into an organic compound<\/li>\r\n \t<li>the use of RuBisCO to form 3-PGA<\/li>\r\n \t<li>the production of carbohydrate molecules from G3P<\/li>\r\n \t<li>the formation of RuBP from G3P molecules<\/li>\r\n \t<li>the use of ATP and NADPH to reduce CO<sub>2<\/sub><\/li>\r\n<\/ol>\r\n<\/div>\r\n<div id=\"fs-idp58557792\">\r\n<p id=\"fs-idm137898064\">[reveal-answer q=\"514998\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"514998\"]<\/p>\r\nA[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"eip-228\">\r\n<div id=\"eip-843\">\r\n<p id=\"eip-558\">If four molecules of carbon dioxide enter the Calvin cycle (four \u201cturns\u201d of the cycle), how many G3P molecules are produced and how many are exported?<\/p>\r\n\r\n<ol id=\"eip-269\" type=\"a\">\r\n \t<li>4 G3P made, 1 G3P exported<\/li>\r\n \t<li>4 G3P made, 2 G3P exported<\/li>\r\n \t<li>8 G3P made, 1 G3P exported<\/li>\r\n \t<li>8 G3P made, 4 G3P exported<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div>\r\n<p id=\"eip-799\">[reveal-answer q=\"190596\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"190596\"]<\/p>\r\nC[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp29027344\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-idm67128928\">\r\n<div id=\"fs-idm190095248\">\r\n<p id=\"fs-idm190094992\">Why is the third stage of the Calvin cycle called the regeneration stage?<\/p>\r\n[reveal-answer q=\"118515\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"118515\"]\r\n<div id=\"fs-idm67128928\">\r\n<div id=\"fs-idm56561952\">\r\n<p id=\"fs-idm122780800\">Because RuBP, the molecule needed at the start of the cycle, is regenerated from G3P.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm56561952\"><\/div>\r\n<\/div>\r\n<div id=\"fs-idm82292544\">\r\n<div id=\"fs-idm82292288\">\r\n<p id=\"fs-idm98126288\">Which part of the light-independent reactions would be affected if a cell could not produce the enzyme RuBisCO?<\/p>\r\n[reveal-answer q=\"708671\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"708671\"]\r\n<div id=\"fs-idm82292544\">\r\n<div id=\"fs-idm83067344\">\r\n<p id=\"fs-idm93212288\">None of the cycle could take place, because RuBisCO is essential in fixing carbon dioxide. Specifically, RuBisCO catalyzes the reaction between carbon dioxide and RuBP at the start of the cycle.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm83067344\"><\/div>\r\n<\/div>\r\n<div id=\"fs-idm107794784\">\r\n<div id=\"fs-idm107794528\">\r\n<p id=\"fs-idp17112800\">Why does it take three turns of the Calvin cycle to produce G3P, the initial product of photosynthesis?<\/p>\r\n[reveal-answer q=\"46869\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"46869\"]\r\n<div id=\"fs-idm107794784\">\r\n<div id=\"fs-idm106433200\">\r\n<p id=\"fs-idp41571024\">Because G3P has three carbon atoms, and each turn of the cycle takes in one carbon atom in the form of carbon dioxide.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm106433200\"><\/div>\r\n<\/div>\r\n<div id=\"eip-148\">\r\n<div id=\"eip-512\">\r\n<p id=\"eip-788\">Imagine a sealed terrarium containing a plant and a beetle. How does each organism provide resources for the other? Could each organism survive if it was the only living thing in the terrarium? Why or why not?<\/p>\r\n\r\n<\/div>\r\n<div id=\"eip-342\">\r\n\r\n[reveal-answer q=\"1939\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"1939\"]\r\n<p id=\"eip-840\">An energy cycle between a plant and a beetle would be as follows:<\/p>\r\n\r\n<ol id=\"eip-267\" type=\"A\">\r\n \t<li>Plant consumes carbon dioxide and releases oxygen as a byproduct of photosynthesis<\/li>\r\n \t<li>Beetle consumes oxygen and releases carbon dioxide to create chemical energy during aerobic respiration<\/li>\r\n \t<li>Plant takes up carbon dioxide from the air<\/li>\r\n \t<li>Repeat cycle<\/li>\r\n<\/ol>\r\n<p id=\"eip-841\">The plant would also provide a carbon-based food source for the beetle.<\/p>\r\n\r\n<ol id=\"eip-268\" type=\"1\">\r\n \t<li>The beetle is a heterotroph, and would not survive without the plant because it would deplete all the oxygen within the terrarium.<\/li>\r\n \t<li>The plant is an autotroph and could survive without the beetle, but it would be unlikely to grow. Through photosynthesis, the plant can make and store its own energy in carbon-based molecules, and produce oxygen. The oxygen can then be used to power aerobic respiration in the plant, which releases carbon dioxide. However, since the plant essentially continues to reuse its own resources cycling between carbon- and oxygen-consuming pathways, its growth would be limited.<\/li>\r\n<\/ol>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"eip-5\">\r\n<div id=\"eip-833\">\r\n<p id=\"eip-107\">Compare the flow of energy with the flow of nutrients in a closed, sunny ecosystem consisting of a giraffe and a tree.<\/p>\r\n[reveal-answer q=\"497474\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"497474\"]\r\n\r\nIn the defined ecosystem, energy would radiate from the Sun, and be absorbed by the chlorophyll in the leaves of the tree. Photosynthesis would occur in the leaves, transforming the light energy into stored chemical energy in the covalent bonds of carbon molecules. The giraffe would eat the leaves of the tree, and digest the carbon molecules to release energy.\r\n<p id=\"eip-4\">In the same ecosystem, nutrients would cycle between the tree and the giraffe. The giraffe would consume oxygen and release carbon dioxide as its cells perform aerobic respiration to create chemical energy. The tree will consume the released carbon dioxide during photosynthesis to create its own stored chemical energy, and release oxygen as a by-product.<\/p>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-idm58645024\">\r\n \t<dt>Calvin cycle<\/dt>\r\n \t<dd id=\"fs-idm135618544\">light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm133703136\">\r\n \t<dt>carbon fixation<\/dt>\r\n \t<dd id=\"fs-idm187501232\">process of converting inorganic CO<sub>2<\/sub> gas into organic compounds<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm8415920\">\r\n \t<dt>reduction<\/dt>\r\n \t<dd id=\"fs-idp97989472\">gain of electron(s) by an atom or molecule<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>Describe the Calvin cycle<\/li>\n<li>Define carbon fixation<\/li>\n<li>Explain how photosynthesis works in the energy cycle of all living organisms<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp47951280\">After the energy from the sun is converted into chemical energy and temporarily stored in ATP and NADPH molecules, the cell has the fuel needed to build carbohydrate molecules for long-term energy storage. The products of the light-dependent reactions, ATP and NADPH, have lifespans in the range of millionths of seconds, whereas the products of the light-independent reactions (carbohydrates and other forms of reduced carbon) can survive almost indefinitely. The carbohydrate molecules made will have a backbone of carbon atoms. But where does the carbon come from? It comes from carbon dioxide\u2014the gas that is a waste product of respiration in microbes, fungi, plants, and animals.<\/p>\n<div id=\"fs-idm160767200\" class=\"bc-section section\">\n<h3>The Calvin Cycle<\/h3>\n<p id=\"fs-idm22256\">In plants, carbon dioxide (CO<sub>2<\/sub>) enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells. Once in the mesophyll cells, CO<sub>2<\/sub> diffuses into the stroma of the chloroplast\u2014the site of light-independent reactions of photosynthesis. These reactions actually have several names associated with them. Another term, the Calvin cycle, is named for the man who discovered it, and because these reactions function as a cycle. Others call it the Calvin-Benson cycle to include the name of another scientist involved in its discovery. The most outdated name is \u201cdark reaction,\u201d because light is not directly required (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_01\">(Figure)<\/a>). However, the term dark reaction can be misleading because it implies incorrectly that the reaction only occurs at night or is independent of light, which is why most scientists and instructors no longer use it.<\/p>\n<div id=\"fig-ch08_03_01\" class=\"wp-caption aligncenter\">\n<div style=\"width: 660px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180513\/Figure_08_03_01.png\" alt=\"This illustration shows that ATP and NADPH produced in the light reactions are used in the Calvin cycle to make sugar.\" width=\"650\" height=\"1197\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1. <\/strong>Light reactions harness energy from the sun to produce chemical bonds, ATP, and NADPH. These energy-carrying molecules are made in the stroma where carbon fixation takes place.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp23499712\">The light-independent reactions of the Calvin cycle can be organized into three basic stages: <em>fixation, reduction, and regeneration.<\/em><\/p>\n<div id=\"fs-idm53150960\" class=\"bc-section section\">\n<h4>Stage 1: Fixation<\/h4>\n<p id=\"fs-idm187183792\">In the stroma, in addition to CO<sub>2<\/sub>, two other components are present to initiate the light-independent reactions: an enzyme called ribulose-1,5-bisphosphate carboxylase\/oxygenase (RuBisCO), and three molecules of ribulose bisphosphate (RuBP), as shown in <a class=\"autogenerated-content\" href=\"#fig-ch08_03_02\">(Figure)<\/a>. RuBP has five atoms of carbon, flanked by two phosphates.<\/p>\n<div id=\"fs-idp117078128\" class=\"art-connection textbox examples\">\n<h3>Art Connection<\/h3>\n<div id=\"fig-ch08_03_02\" class=\"wp-caption aligncenter\">\n<div style=\"width: 360px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180518\/Figure_08_03_02.png\" alt=\"A diagram of the Calvin cycle is shown with its three stages: carbon fixation, 3-PGA reduction, and regeneration of RuBP. In stage 1, the enzyme RuBisCO adds a carbon dioxide to the five-carbon molecule RuBP, producing two three-carbon 3-PGA molecules. In stage 2, two NADPH and two ATP are used to reduce 3-PGA to GA3P. In stage 3 RuBP is regenerated from GA3P. One ATP is used in the process. Three complete cycles produces one new GA3P, which is shunted out of the cycle and made into glucose (C6H12O6).\" width=\"350\" height=\"1345\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 2. <\/strong>The Calvin cycle has three stages. In stage 1, the enzyme RuBisCO incorporates carbon dioxide into an organic molecule, 3-PGA. In stage 2, the organic molecule is reduced using electrons supplied by NADPH. In stage 3, RuBP, the molecule that starts the cycle, is regenerated so that the cycle can continue. Only one carbon dioxide molecule is incorporated at a time, so the cycle must be completed three times to produce a single three-carbon GA3P molecule, and six times to produce a six-carbon glucose molecule.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp27000112\">Which of the following statements is true?<\/p>\n<ol id=\"fs-idm188800912\" type=\"a\">\n<li>In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. GA3P and water are products.<\/li>\n<li>In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. GA3P and oxygen are products.<\/li>\n<li>In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products.<\/li>\n<li>In photosynthesis, water and carbon dioxide are reactants. GA3P and oxygen are products.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q133952\">Show Solution<\/span><\/p>\n<div id=\"q133952\" class=\"hidden-answer\" style=\"display: none\">\n<p>D<\/p><\/div>\n<\/div>\n<\/div>\n<p id=\"fs-idm152383840\">RuBisCO catalyzes a reaction between CO<sub>2<\/sub> and RuBP. For each CO<sub>2<\/sub> molecule that reacts with one RuBP, two molecules of another compound 3-phospho glyceric acid (3-PGA) form. PGA has three carbons and one phosphate. Each turn of the cycle involves only one RuBP and one carbon dioxide and forms two molecules of 3-PGA. The number of carbon atoms remains the same, as the atoms move to form new bonds during the reactions (3 C atoms from 3CO<sub>2<\/sub> + 15 C atoms from 3RuBP = 18 C atoms in 6 molecules of 3-PGA). This process is called carbon fixation, because CO<sub>2<\/sub> is \u201cfixed\u201d from an inorganic form into organic molecules.<\/p>\n<\/div>\n<div id=\"fs-idm89996944\" class=\"bc-section section\">\n<h4>Stage 2: Reduction<\/h4>\n<p id=\"fs-idm86368800\">ATP and NADPH are used to convert the six molecules of 3-PGA into six molecules of a chemical called glyceraldehyde 3-phosphate (G3P). That is a reduction reaction because it involves the gain of electrons by 3-PGA. (Recall that a reduction is the gain of an electron by an atom or molecule.) Six molecules of both ATP and NADPH are used. For ATP, energy is released with the loss of the terminal phosphate atom, converting it into ADP; for NADPH, both energy and a hydrogen atom are lost, converting it into NADP<sup>+<\/sup>. Both of these molecules return to the nearby light-dependent reactions to be reused and re-energized.<\/p>\n<\/div>\n<div id=\"fs-idm23606256\" class=\"bc-section section\">\n<h4>Stage 3: Regeneration<\/h4>\n<p id=\"fs-idm57998960\">Interestingly, at this point, only one of the G3P molecules leaves the Calvin cycle and is sent to the cytoplasm to contribute to the formation of other compounds needed by the plant. Because the G3P exported from the chloroplast has three carbon atoms, it takes three \u201cturns\u201d of the Calvin cycle to fix enough net carbon to export one G3P. But each turn makes two G3Ps, thus three turns make six G3Ps. One is exported while the remaining five G3P molecules remain in the cycle and are used to regenerate RuBP, which enables the system to prepare for more CO<sub>2<\/sub> to be fixed. Three more molecules of ATP are used in these regeneration reactions.<\/p>\n<div id=\"fs-idm132001936\" class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-idm125936400\">This <a href=\"http:\/\/openstaxcollege.org\/l\/calvin_cycle\" target=\"_window\">link<\/a> leads to an animation of the Calvin cycle. Click stage 1, stage 2, and then stage 3 to see G3P and ATP regenerate to form RuBP.<\/p>\n<\/div>\n<div id=\"fs-idm158415504\" class=\"evolution textbox examples\">\n<h3>Evolution Connection<\/h3>\n<p id=\"fs-idm104644592\"><strong>Photosynthesis<\/strong><\/p>\n<p>During the evolution of photosynthesis, a major shift occurred from the bacterial type of photosynthesis that involves only one photosystem and is typically anoxygenic (does not generate oxygen) into modern oxygenic (does generate oxygen) photosynthesis, employing two photosystems. This modern oxygenic photosynthesis is used by many organisms\u2014from giant tropical leaves in the rainforest to tiny cyanobacterial cells\u2014and the process and components of this photosynthesis remain largely the same. Photosystems absorb light and use electron transport chains to convert energy into the chemical energy of ATP and NADH. The subsequent light-independent reactions then assemble carbohydrate molecules with this energy.<\/p>\n<p id=\"fs-idm140187264\">In the harsh dry heat of the desert, plants must conserve every drop of water must be used to survive. Because stomata must open to allow for the uptake of CO<sub>2<\/sub>, water escapes from the leaf during active photosynthesis. Desert plants have evolved processes to conserve water and deal with harsh conditions. Mechanisms to capture and store CO<sub>2<\/sub> allows plants to adapt to living with less water. Some plants such as cacti (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_03\">(Figure)<\/a>) can prepare materials for photosynthesis during the night by a temporary carbon fixation\/storage process, because opening the stomata at this time conserves water due to cooler temperatures. During the day cacti use the captured CO<sub>2<\/sub> for photosynthesis, and keep their stomata closed.<\/p>\n<\/div>\n<div id=\"fig-ch08_03_03\" class=\"wp-caption aligncenter\">\n<div style=\"width: 265px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180521\/Figure_08_03_03.jpg\" alt=\"This photo shows short, round prickly cacti growing in cracks in a rock.\" width=\"255\" height=\"714\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3. <\/strong>The harsh conditions of the desert have led plants like these cacti to evolve variations of the light-independent reactions of photosynthesis. These variations increase the efficiency of water usage, helping to conserve water and energy. (credit: Piotr Wojtkowski)<\/p>\n<\/div>\n<\/div>\n<div class=\"wp-caption-text\"><\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm121372848\" class=\"bc-section section\">\n<h3>The Energy Cycle<\/h3>\n<p id=\"fs-idm186246928\">Whether the organism is a bacterium, plant, or animal, all living things access energy by breaking down carbohydrate and other carbon-rich organic molecules. But if plants make carbohydrate molecules, why would they need to break them down, especially when it has been shown that the gas organisms release as a \u201cwaste product\u201d (CO<sub>2<\/sub>) acts as a substrate for the formation of more food in photosynthesis? Remember, living things need energy to perform life functions. In addition, an organism can either make its own food or eat another organism\u2014either way, the food still needs to be broken down. Finally, in the process of breaking down food, called cellular respiration, heterotrophs release needed energy and produce \u201cwaste\u201d in the form of CO<sub>2<\/sub> gas.<\/p>\n<p id=\"fs-idm154538240\">However, in nature, there is no such thing as \u201cwaste.\u201d Every single atom of matter and energy is conserved, recycled over and over infinitely. Substances change form or move from one type of molecule to another, but their constituent atoms never disappear (<a class=\"autogenerated-content\" href=\"#fig-ch08_03_04\">(Figure)<\/a>).<\/p>\n<p id=\"fs-idp23524720\">In reality, CO<sub>2<\/sub> is no more a form of waste than oxygen is wasteful to photosynthesis. Both are byproducts of reactions that move on to other reactions. Photosynthesis absorbs light energy to build carbohydrates<br \/>\nin chloroplasts, and aerobic cellular respiration releases energy by using oxygen to metabolize carbohydrates in the cytoplasm and mitochondria. Both processes use electron transport chains to capture the energy necessary to drive other reactions. These two powerhouse processes, photosynthesis and cellular respiration, function in biological, cyclical harmony to allow organisms to access life-sustaining energy that originates millions of miles away in a burning star humans call the sun.<\/p>\n<div id=\"fig-ch08_03_04\" class=\"wp-caption aligncenter\">\n<div style=\"width: 430px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03180524\/Figure_08_03_05.jpg\" alt=\"This photograph shows a giraffe eating leaves from a tree. Labels indicate that the giraffe consumes oxygen and releases carbon dioxide, whereas the tree consumes carbon dioxide and releases oxygen.\" width=\"420\" height=\"667\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 4. <\/strong>Photosynthesis consumes carbon dioxide and produces oxygen. Aerobic respiration consumes oxygen and produces carbon dioxide. These two processes play an important role in the carbon cycle. (credit: modification of work by Stuart Bassil)<\/p>\n<\/div>\n<\/div>\n<div class=\"wp-caption-text\"><\/div>\n<\/div>\n<div id=\"fs-idp98484032\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-idm142625264\">Using the energy carriers formed in the first steps of photosynthesis, the light-independent reactions, or the Calvin cycle, take in CO<sub>2<\/sub> from the atmosphere. An enzyme, RuBisCO, catalyzes a reaction with CO<sub>2<\/sub> and another organic compound, RuBP. After three cycles, a three-carbon molecule of G3P leaves the cycle to become part of a carbohydrate molecule. The remaining G3P molecules stay in the cycle to be regenerated into RuBP, which is then ready to react with more CO<sub>2<\/sub>. Photosynthesis forms an energy cycle with the process of cellular respiration. Because plants contain both chloroplasts and mitochondria, they rely upon both photosynthesis and respiration for their ability to function in both the light and dark, and to be able to interconvert essential metabolites.<\/p>\n<\/div>\n<div id=\"fs-idm98385648\" class=\"art-exercise\">\n<h3>Art Connections<\/h3>\n<div id=\"fs-idm60512080\">\n<div id=\"fs-idm185942880\">\n<p id=\"fs-idp5541104\"><a class=\"autogenerated-content\" href=\"#fig-ch08_03_02\">(Figure)<\/a> Which of the following statements is true?<\/p>\n<ol id=\"fs-idm70810960\" type=\"a\">\n<li>In photosynthesis, oxygen, carbon dioxide, ATP, and NADPH are reactants. G3P and water are products.<\/li>\n<li>In photosynthesis, chlorophyll, water, and carbon dioxide are reactants. G3P and oxygen are products.<\/li>\n<li>In photosynthesis, water, carbon dioxide, ATP, and NADPH are reactants. RuBP and oxygen are products.<\/li>\n<li>In photosynthesis, water and carbon dioxide are reactants. G3P and oxygen are products.<\/li>\n<\/ol>\n<\/div>\n<div id=\"fs-idp63246768\">\n<p id=\"fs-idm58178944\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q456097\">Show Solution<\/span><\/p>\n<div id=\"q456097\" class=\"hidden-answer\" style=\"display: none\">\n<p><a href=\"#fig-ch08_03_02\">(Figure)<\/a> D<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm62125584\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-idm107405520\">\n<div id=\"fs-idm48699104\">\n<p id=\"fs-idm36712624\">Which molecule must enter the Calvin cycle continually for the light-independent reactions to take place?<\/p>\n<ol id=\"fs-idm152508560\" type=\"a\">\n<li>RuBisCO<\/li>\n<li>RuBP<\/li>\n<li>3-PGA<\/li>\n<li>CO<sub>2<\/sub><\/li>\n<\/ol>\n<\/div>\n<div id=\"fs-idm47070176\">\n<p id=\"fs-idp2247264\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q941992\">Show Solution<\/span><\/p>\n<div id=\"q941992\" class=\"hidden-answer\" style=\"display: none\">D<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp62052848\">\n<div id=\"fs-idm147194688\">\n<p id=\"fs-idm186510704\">Which order of molecular conversions is correct for the Calvin cycle?<\/p>\n<ol id=\"fs-idm164585152\" type=\"a\">\n<li>[latex]\\text{RuBP\u00a0+\u00a0G3P\u00a0}\\to \\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0sugar}[\/latex]<\/li>\n<li>[latex]\\text{RuBisCO\u00a0}\\to {\\text{\u00a0CO}}_{2}\\text{\u00a0}\\to \\text{\u00a0RuBP\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\n<li>[latex]{\\text{RuBP\u00a0+\u00a0CO}}_{2}\\text{\u00a0}\\to \\text{\u00a0}\\left[\\text{RuBisCO}\\right]\\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\n<li>[latex]{\\text{CO}}_{2}\\text{\u00a0}\\to \\text{\u00a03-PGA\u00a0}\\to \\text{\u00a0RuBP\u00a0}\\to \\text{\u00a0G3P}[\/latex]<\/li>\n<\/ol>\n<\/div>\n<div id=\"fs-idm190120016\">\n<p id=\"fs-idm73937824\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q859746\">Show Solution<\/span><\/p>\n<div id=\"q859746\" class=\"hidden-answer\" style=\"display: none\">\n<p>C<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm99331456\">\n<div id=\"fs-idm99331200\">\n<p id=\"fs-idm24937568\">Where in eukaryotic cells does the Calvin cycle take place?<\/p>\n<ol id=\"fs-idm24937184\" type=\"a\">\n<li>thylakoid membrane<\/li>\n<li>thylakoid lumen<\/li>\n<li>chloroplast stroma<\/li>\n<li>granum<\/li>\n<\/ol>\n<\/div>\n<div id=\"fs-idp62251696\">\n<p id=\"fs-idm152471856\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q654887\">Show Solution<\/span><\/p>\n<div id=\"q654887\" class=\"hidden-answer\" style=\"display: none\">\n<p>C<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm55613456\">\n<div id=\"fs-idm55613200\">\n<p id=\"fs-idp90133632\">Which statement correctly describes carbon fixation?<\/p>\n<ol id=\"fs-idp90134016\" type=\"a\">\n<li>the conversion of CO<sub>2<\/sub> into an organic compound<\/li>\n<li>the use of RuBisCO to form 3-PGA<\/li>\n<li>the production of carbohydrate molecules from G3P<\/li>\n<li>the formation of RuBP from G3P molecules<\/li>\n<li>the use of ATP and NADPH to reduce CO<sub>2<\/sub><\/li>\n<\/ol>\n<\/div>\n<div id=\"fs-idp58557792\">\n<p id=\"fs-idm137898064\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q514998\">Show Solution<\/span><\/p>\n<div id=\"q514998\" class=\"hidden-answer\" style=\"display: none\">\n<p>A<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-228\">\n<div id=\"eip-843\">\n<p id=\"eip-558\">If four molecules of carbon dioxide enter the Calvin cycle (four \u201cturns\u201d of the cycle), how many G3P molecules are produced and how many are exported?<\/p>\n<ol id=\"eip-269\" type=\"a\">\n<li>4 G3P made, 1 G3P exported<\/li>\n<li>4 G3P made, 2 G3P exported<\/li>\n<li>8 G3P made, 1 G3P exported<\/li>\n<li>8 G3P made, 4 G3P exported<\/li>\n<\/ol>\n<\/div>\n<div>\n<p id=\"eip-799\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q190596\">Show Solution<\/span><\/p>\n<div id=\"q190596\" class=\"hidden-answer\" style=\"display: none\">\n<p>C<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp29027344\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-idm67128928\">\n<div id=\"fs-idm190095248\">\n<p id=\"fs-idm190094992\">Why is the third stage of the Calvin cycle called the regeneration stage?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q118515\">Show Solution<\/span><\/p>\n<div id=\"q118515\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm67128928\">\n<div id=\"fs-idm56561952\">\n<p id=\"fs-idm122780800\">Because RuBP, the molecule needed at the start of the cycle, is regenerated from G3P.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm56561952\"><\/div>\n<\/div>\n<div id=\"fs-idm82292544\">\n<div id=\"fs-idm82292288\">\n<p id=\"fs-idm98126288\">Which part of the light-independent reactions would be affected if a cell could not produce the enzyme RuBisCO?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q708671\">Show Solution<\/span><\/p>\n<div id=\"q708671\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm82292544\">\n<div id=\"fs-idm83067344\">\n<p id=\"fs-idm93212288\">None of the cycle could take place, because RuBisCO is essential in fixing carbon dioxide. Specifically, RuBisCO catalyzes the reaction between carbon dioxide and RuBP at the start of the cycle.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm83067344\"><\/div>\n<\/div>\n<div id=\"fs-idm107794784\">\n<div id=\"fs-idm107794528\">\n<p id=\"fs-idp17112800\">Why does it take three turns of the Calvin cycle to produce G3P, the initial product of photosynthesis?<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q46869\">Show Solution<\/span><\/p>\n<div id=\"q46869\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm107794784\">\n<div id=\"fs-idm106433200\">\n<p id=\"fs-idp41571024\">Because G3P has three carbon atoms, and each turn of the cycle takes in one carbon atom in the form of carbon dioxide.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm106433200\"><\/div>\n<\/div>\n<div id=\"eip-148\">\n<div id=\"eip-512\">\n<p id=\"eip-788\">Imagine a sealed terrarium containing a plant and a beetle. How does each organism provide resources for the other? Could each organism survive if it was the only living thing in the terrarium? Why or why not?<\/p>\n<\/div>\n<div id=\"eip-342\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q1939\">Show Solution<\/span><\/p>\n<div id=\"q1939\" class=\"hidden-answer\" style=\"display: none\">\n<p id=\"eip-840\">An energy cycle between a plant and a beetle would be as follows:<\/p>\n<ol id=\"eip-267\" type=\"A\">\n<li>Plant consumes carbon dioxide and releases oxygen as a byproduct of photosynthesis<\/li>\n<li>Beetle consumes oxygen and releases carbon dioxide to create chemical energy during aerobic respiration<\/li>\n<li>Plant takes up carbon dioxide from the air<\/li>\n<li>Repeat cycle<\/li>\n<\/ol>\n<p id=\"eip-841\">The plant would also provide a carbon-based food source for the beetle.<\/p>\n<ol id=\"eip-268\" type=\"1\">\n<li>The beetle is a heterotroph, and would not survive without the plant because it would deplete all the oxygen within the terrarium.<\/li>\n<li>The plant is an autotroph and could survive without the beetle, but it would be unlikely to grow. Through photosynthesis, the plant can make and store its own energy in carbon-based molecules, and produce oxygen. The oxygen can then be used to power aerobic respiration in the plant, which releases carbon dioxide. However, since the plant essentially continues to reuse its own resources cycling between carbon- and oxygen-consuming pathways, its growth would be limited.<\/li>\n<\/ol>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-5\">\n<div id=\"eip-833\">\n<p id=\"eip-107\">Compare the flow of energy with the flow of nutrients in a closed, sunny ecosystem consisting of a giraffe and a tree.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q497474\">Show Solution<\/span><\/p>\n<div id=\"q497474\" class=\"hidden-answer\" style=\"display: none\">\n<p>In the defined ecosystem, energy would radiate from the Sun, and be absorbed by the chlorophyll in the leaves of the tree. Photosynthesis would occur in the leaves, transforming the light energy into stored chemical energy in the covalent bonds of carbon molecules. The giraffe would eat the leaves of the tree, and digest the carbon molecules to release energy.<\/p>\n<p id=\"eip-4\">In the same ecosystem, nutrients would cycle between the tree and the giraffe. The giraffe would consume oxygen and release carbon dioxide as its cells perform aerobic respiration to create chemical energy. The tree will consume the released carbon dioxide during photosynthesis to create its own stored chemical energy, and release oxygen as a by-product.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-idm58645024\">\n<dt>Calvin cycle<\/dt>\n<dd id=\"fs-idm135618544\">light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH<\/dd>\n<\/dl>\n<dl id=\"fs-idm133703136\">\n<dt>carbon fixation<\/dt>\n<dd id=\"fs-idm187501232\">process of converting inorganic CO<sub>2<\/sub> gas into organic compounds<\/dd>\n<\/dl>\n<dl id=\"fs-idm8415920\">\n<dt>reduction<\/dt>\n<dd id=\"fs-idp97989472\">gain of electron(s) by an atom or molecule<\/dd>\n<\/dl>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-693\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":311,"menu_order":4,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-693","chapter","type-chapter","status-publish","hentry"],"part":669,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/693","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":3,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/693\/revisions"}],"predecessor-version":[{"id":2480,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/693\/revisions\/2480"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/parts\/669"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/693\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/media?parent=693"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapter-type?post=693"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/contributor?post=693"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/license?post=693"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}