7091438-Photosynthesis

7091438-Photosynthesis - PHOTOSYNTHESIS Photosynthesis An...

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Unformatted text preview: PHOTOSYNTHESIS Photosynthesis An anabolic, endergonic, carbon dioxide (CO ) requiring process that uses light energy SUN photons glucose Question: Where does photosynthesis take place? Plants Autotrophs: self­producers. Location: 1. Leaves a. stoma b. mesophyll cells Mesophyll Cell Chloroplast Stoma Stomata (stoma) Pores in a plant’s cuticle through which water and gases are exchanged between the plant and the atmosphere. Oxygen (O2) Carbon Dioxide (CO2) Guard Cell Guard Cell Mesophyll Cell Nucleus Cell Wall Chloroplast Central Vacuole Chloroplast Organelle where photosynthesis takes place. Stroma Thylakoid Granum Outer Membrane Inner Membrane Thylakoid Thylakoid Membrane Granum Thylakoid Space Question: Why are plants green? Chlorophyll Molecules Located in the thylakoid membranes. Chlorophyll have Mg+ in the center. Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue­420 nm and red­660 nm are most important). Plants are green because the green wavelength is reflected, not absorbed. Wavelength of Light (nm) 400 500 600 700 Short wave (more energy) Long wave (less energy) Absorption of Chlorophyll Absorption violet blue green yellow wavelength orange red Question: During the fall, what causes the leaves to change colors? Fall Colors In addition to the chlorophyll pigments, there are other pigments present. During the fall, the green chlorophyll pigments are greatly reduced revealing the other pigments. Carotenoids are pigments that are either red or yellow. Redox Reaction The transfer of one or more electrons from one reactant to another. Two types: 1. Oxidation 2. Reduction Oxidation Reaction The loss of electrons from a substance. Or the gain of oxygen. Oxidation 6CO2 + 6H2O → C6H12O6 + 6O2 glucose Reduction Reaction The gain of electrons to a substance. Or the loss of oxygen. Reduction 6CO2 + 6H2O → C6H12O6 + 6O2 glucose Breakdown of Photosynthesis Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Produces energy from solar power (photons) in the form of ATP and NADPH. Breakdown of Photosynthesis 2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C Fixation 1. Light Reaction (Electron Flow) Occurs in the Thylakoid membranes During the light reaction, there are two possible routes for electron flow. A. Cyclic Electron Flow B. Noncyclic Electron Flow A. Cyclic Electron Flow Occurs in the thylakoid membrane. Uses Photosystem I only P700 reaction center­ chlorophyll a Uses Electron Transport Chain (ETC) Generates ATP only ADP + P ATP A. Cyclic Electron Flow SUN Primary Electron Acceptor eeeATP produced by ETC ePhotons P700 Accessory Pigments Photosystem I B. Noncyclic Electron Flow Occurs in the thylakoid membrane Uses PS II and PS I P680 rxn center (PSII) ­ chlorophyll a P700 rxn center (PS I) ­ chlorophyll a Uses Electron Transport Chain (ETC) Generates O2, ATP and NADPH B. Noncyclic Electron Flow Primary Electron Acceptor Primary Electron Acceptor 2eEnzyme Reaction 2eETC 2e- SUN Photon 2eATP P680 2ePhoton P700 NADPH H2O 1/2O2 + 2H+ Photosystem I Photosystem II B. Noncyclic Electron Flow ADP + NADP (Reduced) + (Reduced) P → ATP + H → NADPH Oxygen comes from the splitting of H2O, not CO2 H2O → 1/2 O2 + 2H+ (Oxidized) Chemiosmosis Powers ATP synthesis. Located in the thylakoid membranes. Uses ETC and ATP synthase (enzyme) to make ATP. Photophosphorylation: addition of phosphate to ADP to make ATP. Chemiosmosis SUN H + H+ (Proton Pumping) T PS I high H+ HH concentration + + Thylakoid PS II E C H + H+ H+ H+ H + ATP Synthase Thylakoid Space ADP + P H+ ATP low H+ concentration Calvin Cycle Carbon Fixation (light independent rxn). C3 plants (80% of plants on earth). Occurs in the stroma. Uses ATP and NADPH from light rxn. Uses CO2. To produce glucose: it takes 6 turns and uses 18 ATP and 12 NADPH. Chloroplast Stroma Outer Membrane Inner Membrane Thylakoid Granum Calvin Cycle (C3 fixation) (6C) 6CO2 (36C) 6C-C-C-C-C-C (unstable) 6C-C-C 6ATP 6C-C-C 12PGA (36C) 6ATP 6NADPH (30C) 6C-C-C-C-C RuBP 6ATP 6NADPH 6C-C-C (30C) 6C-C-C 12G3P (6C) (36C) C3 glucose C-C-C-C-C-C Glucose Calvin Cycle Remember: C3 = Calvin Cycle C3 Glucose Photorespiration Occurs on hot, dry, bright days. Stomates close. Fixation of O instead of CO . Produces 2­C molecules instead of 3­C sugar molecules. Produces no sugar molecules or no ATP. 2 2 Photorespiration Because of photorespiration: Plants have special adaptations to limit the effect of photorespiration. 1. C4 plants 2. CAM plants C4 Plants Hot, moist environments. 15% of plants (grasses, corn, sugarcane). Divides photosynthesis spatially. Light rxn ­ mesophyll cells. Calvin cycle ­ bundle sheath cells. C4 Plants Malate C-C-C-C CO2 Malate C-C-C-C Transported CO2 C3 glucose Vascular Tissue C-C-C PEP ATP C-C-C Pyruvic Acid Mesophyll Cell Bundle Sheath Cell CAM Plants Hot, dry environments. 5% of plants (cactus and ice plants). Stomates closed during day. Stomates open during the night. Light rxn ­ occurs during the day. Calvin Cycle ­ occurs when CO2 is present. CAM Plants Night (Stomates Open) Day (Stomates Closed) Vacuole CO2 C-C-C-C Malate C-C-C-C Malate C-C-C-C Malate CO2 C3 C-C-C PEP ATP C-C-C Pyruvic acid glucose Question: Why would CAM plants close their stomates during the day? ...
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