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63 Cards in this Set
- Front
- Back
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What is DCMU?
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It is a broad spectrum herbicide that functions by blocking electron flow through photosystem II and is used to reduce weeds in non-crop areas
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What is paraquat?
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It prevents the reduction of NADP+ by accepting electrons from intermediate reductants in photosystem I
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What is the photosynthetic electron transport system often referred to as?
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It is often referred to as the light reactions of photosynthesis
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What is the Calvin cycle sometimes called?
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It is sometimes called the dark reactions
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When is the calvin cycle most active?
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In the light when ATP and NADPH levels are high
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Where does the Calvin cycle take place?
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It takes place in the stroma
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What is the combined reaction for photosythetic ETC and carbon fixation?
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H2O + CO2 ---(light energy)---> O2 + (CH2O)
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Since six CO2 molecules are required for the synthesis of each molecule of glucose by the Calvin cycle, this reaction can be rewritten as what?
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6 H2O + 6 CO2 ---(light energy)---> C6H12O6 + 6 O2
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What is the change in standard free energy for this reaction and how is it overcome?
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The change in standard free energy (Gº') for this reaction is +2868 kJ/mol which is overcome by
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What does the photosynthetic electron transport system and Calvin cycle accomplish for the cell?
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The photosynthetic electron transport system converts light energy into redox energy which is used to generate ATP by chemiosmosis and reduce NADP+ to form NADPH. Calvin cycle enzymes use energy available from ATP and NADPH to reduce CO2 to form glyceraldehyde-3-P, a three carbon carbohydrate used to synthesize glucose.
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What are the overall net reactions of photosynthetic electron transport system and the Calvin cycle?
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Photosynthetic electron transport system (production of ATP and O2): 2 H2O + 8 photons + 2 NADP+ + ~3 ADP + ~3 Pi ------>O2 + 2 NADPH + ~3 ATP
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What are the key enzymes in the photosynthetic electron transport system and the Calvin cycle?
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Protein components of the photosynthetic electron transport system
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What are the protein components of the photosynthetic ETC needed for?
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They are required for the oxidation of H2O and reduction of NADP+
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What is Chloroplast ATP synthetase responsible for?
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It is responsible for the process of photophosphorylation which converts proton-motive force (energy available from the electrochemical proton gradient) into net ATP synthesis through a series of proton-driven conformational changes.
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What is Cholorplast ATP synthetase similar to?
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This enzyme is very similar to mitochondrial ATP synthetase in both structure and function.
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What is Ribulose 1,5 bisphosphate carboxylate/oxygenase responsible for?
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It is responsible for CO2 fixation in the first step of the Calvin cycle.
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What are examples of the photosynthetic electron transport system and Calvin cycle in real life?
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Many types of herbicides block photosynthetic electron transport through photosystem II or function as photosystem I electron acceptors. Accidental exposure to herbicides is not generally harmful to humans, however, Agent Orange, a mixture of herbicides used in the Viet Nam war,
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What do chlorophyll molecules convert light energy into?
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They convert light energy into redox energy
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What does the chloroplast stroma function to do?
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It functions the same way as the matrix of the mitochondria with the exception that protons are pumped into the thylakoid lumen and dlow out through the ATP synthase complex toward the stroma
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Where is light energy absorbed?
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It is absorbed by numerous accessory pigments
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What do these accessory pigments do for the light?
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They transfer the absorbed energy to nearby reaction centers containing specialized chlorophyll molecules
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What do these accessory pigments function as?
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Light harvesting antenna
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What does photon absorption of the appropriate wavelength do?
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It excites an electron from its ground state and lifts it to a higher orbital
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What is an electron said to be at this point?
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"Excited"
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What happens in most cases to these electrons?
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The chlorophyll electron will return to its ground state
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What does it do with its absorbed energy?
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It transfers the absorbed energy to a nearby chlorophyll molecule through a process called resonance energy transfer or exciton transfer
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What is the second possibility of what can happen to the excited chlorophyll electron?
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It can be transferred to a nearby acceptor molecule of lower reduction potential
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What does this result in?
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It results in oxidation of the chlorophyll molecule (loss of electron) and reduction of the acceptor molecule (gain of electron)
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What is this reaction called?
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It is called photooxidation or energy transduction
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Where does photooxidation take place, and what is it key for?
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It takes place in reaction centers and is the key to energy conversion in photosynthesis
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Why is it key?
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Because it results in photoinduced charge separation
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What happens to the reduced acceptor molecule after photooxidation occurs?
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It donates the electron to another acceptor molecule of lower reduction potential and thereby activates the photosynthetic electron transport system
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What importantly happens to the oxidized chlorophyll molecule next?
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It returns to the ground state by accepting an electron through a coupled redox reaction involving the oxidation of H2O
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Where does this process of O2 evolution take place?
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It takes place in the manganese center present in the thylakoid membrane
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How does H2O's role in photosynthesis relate to the role of NADH and FADH2 in mitochondrial electron transport?
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It has the same role as they do
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What are the two types of cholorophylls called in plants?
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Chlorophyll a and chlorophyll b
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How do they differ?
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They differ only slightly in the structure of the heterocyclic ring
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What does the difference in structure of the two do to their absorption of light?
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They absorb light in the blue (400 - 500 nm) and red (600 - 700 nm) slightly differently
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At what wavelength does the PSII reaction center complex absorb light?
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680 nm
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At what wavelength does the PSI reaction center complex absorb light?
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700 nm
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How are the two photosystem reaction center complexes linked?
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They are linked by an electron carrier protein called plastocyanin
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What does plasocyanin do?
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It shuttles electrons one at a time from PSII to PSI
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What does photooxidation by chlorophyll molecules release?
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It releases an electron that can be used for chemical work by a series of coupled redox reactions
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What does the oxidation of 2 H2O require?
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It requires 8 photons to transport 4 electrons through the system
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What does this result in?
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It results in the accumulation of 12 H+ in the thylakoid space and the generation of 2 NADPH in the stroma
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What does the photosynthetic electron transport system in plants consist of?
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It consists of two linked electron circuits
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What do these two linked electron circuits require?
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They require an input of energy from light absorption at PSII and PSI
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How does plastocyanin's job relate to cytochrome c?
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It has the same job in photosynthetic electron transport as does cyctochrome c does in mitochondrial electron transport
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What does the absorption of light energy in PS II result in?
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It results in proton pumping through the cytochrome bf complex
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What is light energy absorbed in PS I used for?
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It is used to reduce NADP+ to form NADPH
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What is this NADPH used for then?
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It is used in the Calvin Cycle to generate carbohydrates from CO2 fixation
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How many photons need to be absorbed by which reaction center for one electron to be transported through the Z scheme from H2O to NADP+?
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One photon needs to be absorbed by each reaction center
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How many photons are required to transport the four electrons obtained from the oxidation of 2 H2O?
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Eight photons are required
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Electron flow through PSII resulting from the absorption of 4 photons leads to the reduction of two molecules of what?
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plastoquinone (Q)
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What does this generate in the process?
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It generates a net increase of 4 H+ inside the thylakoid lumen
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What does the cytochrome bf complex link?
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It links photosystem II to photosystem I
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What is the total number of H+ molecules accumulated inside the thylakoid membrane for every O2 generated in PS II?
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12 H+ molecules are accumulated for every O2 generated in PS II
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In PS I, when 4 photons are absorbed, what is the energy used for?
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It is used to generate reduced ferredoxin
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What is ferredoxin?
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It is a powerful reductant that will reduce NADP+ to generate NADPH
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Does electron flow through PS I result in H+ translocation?
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No
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What does ferredoxin-NADP+ reductase do?
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It converts NADP+ to NADPH
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Are oxidative phosphorylation and photosynthesis related, and if so- how?
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The light induced proton motive force generated during photosynthesis is used to generate ATP in the stroma as a result of protons moving out of the thylakoid lumen
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How do photosynthetic reaction centers convert light energy into redox energy?
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They do it through photon absorption by chlorophyll molecules in the PS II and PS I reaction center complexes
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