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29 Cards in this Set
- Front
- Back
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Where does photosynthesis occur?
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in the chloroplasts
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stroma
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A thick fluid enclosed by the inner membrane of a chloroplast. Sugars are made in the stroma by the enzymes of the Calvin cycle.
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thylakoid
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One of a number of disk-shaped membranous sacs inside a chloroplast. Thylakoid membranes contain chlorophyll and the enzymes of the light reactions of photosynthesis. A stack of thylakoids is called a granum
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granum
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A stack of hollow disks formed of thylakoid membrane in a chloroplast. Grana are the sites where light energy is trapped by chlorophyll and converted to chemical energy during the light reactions of photosynthesis.
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Reactants and products of photosynthesis
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6 CO2 +6 H2O ---->Light energy ------> C6H12O6 + 6 O2
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What are the sites of light reactions?
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The thylakoids inside the chloroplasts
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light reactions
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The first of two stages in photosynthesis, the steps in which solar energy is absorbed and converted to chemical energy in the form of ATP and NADPH. The light reactions power the sugar-producing Calvin cycle but produce no sugar themselves.
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NADPH
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An electron carrier involved in photosynthesis. Light drives electrons from chlorophyll to NADP+, forming NADPH, which provides the high-energy electrons for the reduction of carbon dioxide to sugar in the Calvin cycle.
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Calvin cycle
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The second of two stages of photosynthesis; a cyclic series of chemical reactions that occur in the stroma of a chloroplast, using the carbon in CO2 and the ATP and NADPH produced by the light reactions to make the energy-rich sugar molecule G3P.
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For chloroplasts to produce sugar from carbon dioxide in the dark, they would require an artificial supply of the molecules ___________ and ___________.
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ATP
NADPH |
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What are the primary inputs and outputs of the Calvin cycle?
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Inputs: CO2, ATP, NADPH
output: glucose |
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wavelength
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The distance between crests of adjacent waves, such as those of the electromagnetic spectrum.
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electromagnetic spectrum
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The full range of radiation, from the very short wavelengths of gamma rays to the very long wavelengths of radio signals.
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chlorophyll a
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absorbs mainly blue-violet and red light. A green pigment in chloroplasts that participates directly in the light reactions.
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chlorophyll b
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Does not participate directly in the light reactions. Absorbs mainly blue and orange light
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photon
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A fixed quantity of light energy. The shorter the wavelength of light, the greater the energy of a photon.
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photosystem
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A light-harvesting unit of a chloroplast’s thylakoid membrane; consists of several hundred antenna molecules, a reaction-center chlorophyll, and a primary electron acceptor.
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reaction center
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In a photosystem in a chloroplast, the chlorophyll a molecule and the primary electron acceptor that trigger the light reactions of photosynthesis. The chlorophyll donates an electron excited by light energy to the primary electron acceptor, which passes an electron to an electron transport chain.
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What are the inputs for the calvin cycle?
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CO2
ATP NADPH |
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What are the outputs from the calvin cycle?
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G3P
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The Calvin cycle.
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The cycle produces one G3P sugar molecule for every three CO2 molecules that enter the cycle. Carbon enters the cycle as CO2. An enzyme adds the CO2 to RuBP (ribulose bisphosphate), a five-carbon sugar. (In the diagram, represents a phosphate group.) The product then breaks into a three-carbon compound called 3-PGA (3-phosphoglyceric acid). Enzymes use the ATP energy and high-energy NADPH electrons from the light reactions to convert the 3-PGA to a three-carbon sugar, G3P (glyceraldehyde 3-phosphate). The cycle has converted three CO2 molecules to one molecule of the sugar G3P. This is the direct product of photosynthesis, but plant cells can use the G3P to make glucose and other organic compounds for growth and fuel. The cycle regenerates its starting material. Note that of the six G3P molecules produced in step 3, only one of them represents net sugar output. That’s because we started with a total of 15 sugar carbons in the three RuBP molecules that accepted CO2 back in step 1. Enzymes now regenerate the RuBP by rearranging the five G3P molecules that are left after one of those sugars exits the cycle.
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C3 plant
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A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.
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C4 plant
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A plant that prefaces the Calvin cycle with reactions that incorporate CO2 into four-carbon compounds, the end product of which supplies CO2 for the Calvin cycle.
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C4 and CAM photosynthesis compared.
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Both adaptations are characterized by the preliminary incorporation of CO2 into four-carbon compounds, followed by the transfer of the CO2 to the Calvin cycle. (a) In C4 plants, such as sugarcane, these two steps are separated spatially; they are segregated into two cell types. (b) In CAM plants, such as pineapple, the two steps are separated in time; carbon incorporation into four-carbon compounds occurs at night, and the Calvin cycle operates during the day. The C4 and CAM pathways are two evolutionary solutions to the problem of maintaining photosynthesis with stomata partially or completely closed on hot, dry days.
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CAM plant
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A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. Carbon dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.
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In terms of the spatial organization of photosynthesis within the chloroplast, what is the advantage of the light reactions producing NADPH and ATP on the stroma side of the thylakoid membrane?
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The Calvin cycle, which consumes the NADPH and ATP, occurs in the stroma.
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What is the function of NADPH in the Calvin cycle?
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It provides the high-energy electrons that are added to CO2 to form sugar.
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How do special enzymes enable C4 and CAM plants to conserve water during photosynthesis?
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By allowing photosynthesis to continue even when stomata are closed during dry conditions
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greenhouse effect
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The warming of the atmosphere caused by CO2, CH4, and other gases that absorb infrared radiation and slow its escape from Earth’s surface.
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