Photosynthesis- Light Reactions (Chapter 10)

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-light reaction use water and light (outside of cell brought in), NADP+, Phosphorus, and ADP (created by calvin cycle) to produce NADPH, ATP (both used in calvin cycle) and O2 (waste product)
- the light excites the electrons, the excited electrons energy is then used to join ADP and Phosphate together to form ATP
-NADP+ the joins with the excited electrons to form NADPH which temperately stores the excited electrons.
- in the process water is split and O2 formed as waste and released.
(In the light reactions, the energy of sunlight is used to oxidize water (the electron donor) to O2 and pass these electrons to NADP+, producing NADPH. Some light energy is used to convert ADP to ATP. The NADPH and ATP produced are subsequently used to power the sugar-producing Calvin cycle.)
Calvin CycleEnergy from ATP, electrons from NADPH (both created from light reactions) and carbon from CO2 (brought in from outside) are combined to create sugar. - produces sugar, NADP+, ADP and phosphate (last 3 used again in light reactions) -(In the Calvin cycle, the energy outputs from the light reactions (ATP and NADPH) are used to power the conversion of CO2 into the sugar G3P. As ATP and NADPH are used, they produce ADP and NADP+, respectively, which are returned to the light reactions so that more ATP and NADPH can be formed.)Connection between mitochondria and chloroplast?A mutually dependent relationship exists between chloroplasts and mitochondria in the plant cell. Photosynthesis, which occurs in chloroplasts, generates the sugars and oxygen gas that are used in mitochondria for cellular respiration. Cellular respiration generates carbon dioxide, which in turn is used as a carbon source for the synthesis of sugars during photosynthesis. Cellular respiration also generates ATP and water, which are used in various chemical reactions in the plant cell._____ provides energy for ____ that occurs in ____ contains the pigment ____sunlight...photosynthesis...chloroplasts....chlorophyllphotosynthesis produces ____ and ____ that are inputs for _____ that occurs in the ____ and produces ____ and ____oxygen and sugar...cellular respiration...mitochondria... carbon dioxide and ATPthe carbon dioxide produced in cellular respiration provides carbon for ____photosynthesis.photosynthesis and cellular respirationInputs of light reactionslight, water, NADP+, ADPOutputs of light reactionsNADPH, ATP, O2Inputs of Calvin CycleCO2, ATP, NADPHOutputs of Calvin CycleNADP+, ADP, G3P (sugar)In the light reactions, light energy is used to oxidize ____ to ____- H2O to O2 -In the light reactions, light energy is used to remove electrons from (oxidize) water, producing O2 gas.The electrons derived from this oxidation reaction in the light reactions are used to reduce ___ to ___-NADP+ to NADPH -These electrons (from oxidation of H2O to O2) are ultimately used to reduce NADP+ to NADPH.The Calvin cycle oxidizes the light-reactions product ___ to ___- NADPH to NADP+ -In the Calvin cycle, NADPH is oxidized back to NADP+ (which returns to the light reactions).The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce ___ to ____-CO2 to G3P -The electrons released by the oxidation of NADPH are used to reduce three molecules of CO2 to sugar (G3P), which then exits the Calvin cycle.Overview of ChloroplastThe chloroplast is enclosed by a pair of envelope membranes (inner and outer) that separate the interior of the chloroplast from the surrounding cytosol of the cell. Inside the chloroplast, the chlorophyll-containing thylakoid membranes are the site of the light reactions. Between the inner envelope membrane and the thylakoid membranes is the aqueous stroma, which is the location of the reactions of the Calvin cycle. Inside the thylakoid membranes is the thylakoid space, where protons accumulate during ATP synthesis in the light reactions.Photosystem II-oxidation of water reduction of electron transport chain between the two photosystems -In PS II (the first photosystem in the sequence), P680 is oxidized (which in turn oxidizes water), and the PS II primary electron acceptor is reduced (which in turn reduces the electron transport chain between the photosystems).Photosystem I-reduction of NADP+ oxidation of electron transport chain between the two photosystems -In PS I, the PS I primary electron acceptor is reduced (which in turn reduces other compounds that ultimately reduce NADP+ to NADPH), and P700 is oxidized (which in turn oxidizes the electron transport chain between the photosystems).Photosystem I and Photosystem II-light absorption, reduction of primary electron acceptor - The key function of each of the two photosystems is to absorb light and convert the energy of the absorbed light into redox energy, which drives electron transport.Energy in Photosystems I and IIIn both PS II and PS I, light energy is used to drive a redox reaction that would not otherwise occur. In each photosystem, this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem's primary electron acceptor. The result in each case is a reductant (the reduced primary electron acceptor) and an oxidant (P680+ in PS II and P700+ in PS I) that are able to power the rest of the electron transfer reactions without further energy input.Energy required? 1) Water to P680+ 2) P680 tp Pq (plastoquinone) 3) Pq to P700+ 4) P700 to Fd (ferredoxin) 5) Fd to NADP+1) no energy 2) energy 3) no energy 4) energy 5) no energyProton gradient formation and ATP synthesis-ATP synthesis in chloroplasts is very similar to that in mitochondria: Electron transport is coupled to the formation of a proton (H+) gradient across a membrane. The energy in this proton gradient is then used to power ATP synthesis. -Photosynthetic electron transport contributes to the formation of a proton (H+) gradient across the thylakoid membrane in two places. -In PS II, the oxidation of water releases protons into the thylakoid space. (H+ release site) -Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space. -The resulting proton gradient is used by the ATP synthase complex to convert ADP to ATP in the stroma. by diffusing H+ across the membrane (out of thylakoid space into stroma)What wavelengths drive photosynthesis (Experiment Engelmann)In this experiment, Engelmann was able to determine which wavelengths (colors) of light are most effective at driving photosynthesis. First, Engelmann used a prism to disperse white light from the sun into the colors (wavelengths) of the visible spectrum. Then, using a microscope, he illuminated a filament of green algae with the visible spectrum. The photosynthetic pigments in the alga absorbed some of the wavelengths of light, using the absorbed energy to drive the reactions of photosynthesis, including oxygen production. Engelmann used his recently discovered aerotactic bacteria to determine which wavelengths of light caused the alga to photosynthesize most. Because the aerotactic bacteria were attracted to areas of highest oxygen concentration, they congregated around the regions of the alga that photosynthesized the most. He then counted the bacteria associated with each region of the alga illuminated by the various colors of light. Engelmann found that some wavelengths of light attracted more bacteria, suggesting that these wavelengths drive more photosynthesis than others.Assumptions of EngelmannFor Engelmann to be able to draw meaningful conclusions from his experiment, he had to assume that the number of bacteria at any location on the slide was proportional to the amount of oxygen produced by the alga at that location. If this were not the case, the distribution of the bacteria around the alga would be of no use in determining the amount of photosynthesis that occurs at each wavelength. Similarly, it was necessary for Engelmann to assume that the distribution of chloroplasts among the cells in the algal filament was approximately equal. Fewer chloroplasts in one cell compared to another would mean a lower potential for oxygen production at any color. Engelmann's microscope was sufficiently powerful to see that Cladophora cells contain many small chloroplasts that were nearly uniform in their distribution within and between cells. In contrast, Engelmann did not assume that the alga absorbed the same number of photons at each wavelength. In fact, most photosynthetic pigments absorb more strongly in the red and blue parts of the spectrum and less strongly in the yellow and green parts. He also did not assume that all absorbed photons drive photosynthesis, and thus oxygen production, by the alga. In fact, all photosynthetic organisms contain some pigments that absorb photons but do not contribute to photosynthesis or oxygen production.Colors with most PhoyosynthesisViolet-Blue and RedWhich of these phosphorylates ADP to make ATP?ATP Synthase_____ releases energy that is used to pump hydrogen ions from the stroma into the thylakoid compartment.-ETC -The energy released as electrons are passed along the electron transport chain is used to pump protons into the thylakoid compartment._____ splits water into 1/2 O2, H+, and e- .Photosystem II splits water into 1/2 O2, H+, and e-Energized electrons from ____ enter an electron transport chain and are then used to reduce NADP+.Energized electrons from photosystem I are used to reduce NADP+.Chlorophyll can be found in _____.Photosystem I and IIWhich term describes ATP production resulting from the capture of light energy by chlorophyll?PhotophosphorylationAccording to the chemiosmotic hypothesis, what provides the energy that directly drives ATP synthesis?A proton gradient across chloroplast and mitochondrial membranes drives ATP synthesis by the enzyme ATP synthase.Which of the following particles can pass through the ATP synthase channel?The channels formed by ATP synthase are specific for protons.True or false? The region of ATP synthase that catalyzes the production of ATP from ADP and inorganic phosphate spans the chloroplast membrane.The region of ATP synthase that catalyzes ATP production protrudes out of, but does not span, the chloroplast membrane; the region that spans the membrane is an ion channel through which protons can pass.