Using Light to Make Organic Molecules Quiz

PDF page 356: The free energy stored in ATP and NADPH produced in the light-dependent reactions is used to power the chemical reactions of the light-independent reactions or Calvin cycle, which can occur during both the day and night. In the Calvin cycle, an enzyme called ribulose biphosphate carboxylase (RuBisCO), catalyzes a reaction with CO2 and another molecule called ribulose biphosphate (RuBP) that is regenerated from a previous Calvin cycle. After a series of chemical reactions, the carbon from carbon dioxide in the atmosphere is “fixed” into carbohydrates, specifically a three-carbon molecule called glyceraldehydes-3-phosphate (G3P). (Again, count the carbons as we explore the Calvin cycle.) After three turns of the cycle, 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 incoming CO2. In other words, the cell generates a stockpile of G3P to be assembled into organic molecules, including carbohydrates. Each step of the Calvin cycle is catalyzed by specific enzymes. (You do not have to memorize the reactions of the Calvin cycle; however, if provided with a diagram of the cycle, you should be able to interpret it.) Some plants evolved chemical modifications to more efficiently trap CO2 if environmental conditions limit its availability. For example, when it’s hot outside, plants tend to keep their stomata closed to prevent excessive water loss; when the outside temperature cools, stomata open and plants take in CO2 and use a more efficient system to feed it into the Calvin cycle. As we explored in Overview of Photosynthesis, photosynthesis forms an energy link with cellular respiration. Plants need both photosynthesis and respiration in order to conduct metabolic processes during both light and dark times. Therefore, plant cells contain both chloroplasts and mitochondria. Information presented and the examples highlighted in the section, support concepts and learning objectives outlined

PDF page 365: Using the energy carriers formed in the first steps of photosynthesis, the light-independent reactions, or the Calvin cycle, take in CO2 from the environment. An enzyme, RuBisCO, catalyzes a reaction with CO2 and another molecule, RuBP.

PDF page 356: The free energy stored in ATP and NADPH produced in the light-dependent reactions is used to power the chemical reactions of the light-independent reactions or Calvin cycle, which can occur during both the day and night. In the Calvin cycle, an enzyme called ribulose biphosphate carboxylase (RuBisCO), catalyzes a reaction with CO2 and another molecule called ribulose biphosphate (RuBP) that is regenerated from a previous Calvin cycle. After a series of chemical reactions, the carbon from carbon dioxide in the atmosphere is “fixed” into carbohydrates, specifically a three-carbon molecule called glyceraldehydes-3-phosphate (G3P). (Again, count the carbons as we explore the Calvin cycle.) After three turns of the cycle, 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 incoming CO2. In other words, the cell generates a stockpile of G3P to be assembled into organic molecules, including carbohydrates. Each step of the Calvin cycle is catalyzed by specific enzymes. (You do not have to memorize the reactions of the Calvin cycle; however, if provided with a diagram of the cycle, you should be able to interpret it.) Some plants evolved chemical modifications to more efficiently trap CO2 if environmental conditions limit its availability. For example, when it’s hot outside, plants tend to keep their stomata closed to prevent excessive water loss; when the outside temperature cools, stomata open and plants take in CO2 and use a more efficient system to feed it into the Calvin cycle. As we explored in Overview of Photosynthesis, photosynthesis forms an energy link with cellular respiration. Plants need both photosynthesis and respiration in order to conduct metabolic processes during both light and dark times. Therefore, plant cells contain both chloroplasts and mitochondria. Information presented and the examples highlighted in the section, support concepts and learning objectives outlined

PDF page 359: RuBisCO catalyzes a reaction between CO2 and RuBP. For each CO2 molecule that reacts with one RuBP, two molecules of another compound (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 atoms from 3CO2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called carbon fixation, because CO2 is “fixed” from an inorganic form into organic molecules. Stage 2: Reduction 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

PDF page 359: Figure 8.19 The Calvin cycle has three stages. In stage 1, the enzyme RuBisCO incorporates carbon dioxide into

PDF page 359: 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 threecarbon GA3P molecule, and six times to produce a six-carbon glucose molecule. Which of the following statements is true?

PDF page 358: The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration. Stage 1: Fixation In the stroma, in addition to CO2, 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 Figure 8.19. RuBP has five atoms of carbon, flanked by two phosphates.

PDF page 358: The light-independent reactions of the Calvin cycle can be organized into three basic stages: fixation, reduction, and regeneration. Stage 1: Fixation In the stroma, in addition to CO2, 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 Figure 8.19. RuBP has five atoms of carbon, flanked by two phosphates.

PDF page 359: RuBisCO catalyzes a reaction between CO2 and RuBP. For each CO2 molecule that reacts with one RuBP, two molecules of another compound (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 atoms from 3CO2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called carbon fixation, because CO2 is “fixed” from an inorganic form into organic molecules. Stage 2: Reduction 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

PDF page 359: RuBisCO catalyzes a reaction between CO2 and RuBP. For each CO2 molecule that reacts with one RuBP, two molecules of another compound (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 atoms from 3CO2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called carbon fixation, because CO2 is “fixed” from an inorganic form into organic molecules. Stage 2: Reduction 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

PDF page 364: absorption spectrum range of wavelengths of electromagnetic radiation absorbed by a given substance antenna protein pigment molecule that directly absorbs light and transfers the energy absorbed to other pigment molecules Calvin cycle light-independent reactions of photosynthesis that convert carbon dioxide from the atmosphere into carbohydrates using the energy and reducing power of ATP and NADPH carbon fixation process of converting inorganic CO2 gas into organic compounds carotenoid photosynthetic pigment that functions to dispose of excess energy chemoautotroph organism that can build organic molecules using energy derived from inorganic chemicals instead of sunlight chlorophyll a form of chlorophyll that absorbs violet-blue and red light and consequently has a bluish-green color; the only pigment molecule that performs the photochemistry by getting excited and losing an electron to the electron transport chain chlorophyll b accessory pigment that absorbs blue and red-orange light and consequently has a yellowish-green tint chloroplast organelle in which photosynthesis takes place cytochrome complex group of reversibly oxidizable and reducible proteins that forms part of the electron transport chain between photosystem II and photosystem I electromagnetic spectrum range of all possible frequencies of radiation electron transport chain group of proteins between PSII and PSI that pass energized electrons and use the energy released by the electrons to move hydrogen ions against their concentration gradient into the thylakoid lumen granum stack of thylakoids located inside a chloroplast heterotroph organism that consumes organic substances or other organisms for food light harvesting complex complex that passes energy from sunlight to the reaction center in each photosystem; it consists of multiple antenna proteins that contain a mixture of 300–400 chlorophyll a and b molecules as well as other pigments like carotenoids light-dependent reaction first stage of photosynthesis where certain wavelengths of the visible light are absorbed to form two energy-carrying molecules (ATP and NADPH) light-independent reaction second stage of photosynthesis, though which carbon dioxide is used to build carbohydrate molecules using energy from ATP and NADPH

PDF page 359: RuBisCO catalyzes a reaction between CO2 and RuBP. For each CO2 molecule that reacts with one RuBP, two molecules of another compound (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 atoms from 3CO2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called carbon fixation, because CO2 is “fixed” from an inorganic form into organic molecules. Stage 2: Reduction 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

PDF page 359: RuBisCO catalyzes a reaction between CO2 and RuBP. For each CO2 molecule that reacts with one RuBP, two molecules of another compound (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 atoms from 3CO2 + 15 atoms from 3RuBP = 18 atoms in 3 atoms of 3-PGA). This process is called carbon fixation, because CO2 is “fixed” from an inorganic form into organic molecules. Stage 2: Reduction 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

PDF page 357: 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 lightindependent reactions (carbohydrates and other forms of reduced carbon) can survive for hundreds of millions of years. The carbohydrate molecules made will have a backbone of carbon atoms. Where does the carbon come from? It comes from carbon dioxide, the gas that is a waste product of respiration in microbes, fungi, plants, and animals. In plants, carbon dioxide (CO2) 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, CO2 diffuses into the stroma of the chloroplast—the 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 dark reactions, because light is not directly required (Figure 8.18). 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.

PDF page 357: 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 lightindependent reactions (carbohydrates and other forms of reduced carbon) can survive for hundreds of millions of years. The carbohydrate molecules made will have a backbone of carbon atoms. Where does the carbon come from? It comes from carbon dioxide, the gas that is a waste product of respiration in microbes, fungi, plants, and animals. In plants, carbon dioxide (CO2) 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, CO2 diffuses into the stroma of the chloroplast—the 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 dark reactions, because light is not directly required (Figure 8.18). 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.

PDF page 357: 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 lightindependent reactions (carbohydrates and other forms of reduced carbon) can survive for hundreds of millions of years. The carbohydrate molecules made will have a backbone of carbon atoms. Where does the carbon come from? It comes from carbon dioxide, the gas that is a waste product of respiration in microbes, fungi, plants, and animals. In plants, carbon dioxide (CO2) 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, CO2 diffuses into the stroma of the chloroplast—the 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 dark reactions, because light is not directly required (Figure 8.18). 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.

PDF page 364: mesophyll middle layer of chlorophyll-rich cells in a leaf P680 reaction center of photosystem II P700 reaction center of photosystem I photoact ejection of an electron from a reaction center using the energy of an absorbed photon photoautotroph organism capable of producing its own organic compounds from sunlight photon distinct quantity or “packet” of light energy photosystem group of proteins, chlorophyll, and other pigments that are used in the light-dependent reactions of photosynthesis to absorb light energy and convert it into chemical energy