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Unformatted text preview: PHOTOSYNTHESIS PHOTOSYNTHESIS QBA Miguel A. Castro Ramírez Photosynthesis Photosynthesis • An anabolic, endergonic, carbon dioxide (CO ) requiring process that uses light energy (CO SUN photons glucose glucose Question: Question: • Where does photosynthesis take place? Plants Plants • Autotrophs: self-producers. • Location: 1. Leaves a. stoma b. mesophyll cells Mesophyll Cell Chloroplast Stoma Stomata (stoma) Stomata • Pores in a plant’s cuticle through which water water and gases are exchanged between the plant gases and the atmosphere. Oxygen (O2) Carbon Dioxide (CO2) Guard Cell Guard Cell Mesophyll Cell Mesophyll Nucleus Cell Wall Chloroplast Central Vacuole Chloroplast Chloroplast • Organelle where photosynthesis takes place. photosynthesis Stroma Outer Membrane Inner Membrane Thylakoid Granum Thylakoid Thylakoid Thylakoid Membrane Granum Thylakoid Space Question: Question: • Why are plants green? Chlorophyll Molecules Chlorophyll • Located in the thylakoid membranes. thylakoid • Chlorophyll have Mg+ in the center. Mg • Chlorophyll pigments harvest energy (photons) by absorbing certain wavelengths (blue-420 absorbing wavelengths blue-420 nm and red-660 nm are most important). nm • Plants are green because the green green wavelength is reflected, not absorbed. wavelength reflected not Wavelength of Light (nm) Wavelength 400 500 600 700 Short wave (more energy) Long wave (less energy) Absorption of Chlorophyll Absorption Absorption violet blue green yellow wavelength orange red Question: Question: • During the fall, what causes the leaves to During change colors? change Fall Colors Fall • In addition to the chlorophyll pigments, there are other pigments present. pigments • During the fall, the green chlorophyll pigments green are greatly reduced revealing the other greatly pigments. pigments • Carotenoids are pigments that are either red or red yellow. yellow Redox Reaction Redox • The transfer of one or more electrons from transfer one more one reactant to another. one another • Two types: 1. Oxidation 2. Reduction Oxidation Reaction Oxidation • The loss of electrons from a substance. loss electrons • Or the gain of oxygen. gain oxygen Oxidation 6CO2 + 6H2O → C6H12O6 + 6O2 glucose Reduction Reaction Reduction • The gain of electrons to a substance. gain • Or the loss of oxygen. loss oxygen Reduction 6CO2 + 6H2O → C6H12O6 + 6O2 glucose Breakdown of Photosynthesis Breakdown • Two main parts (reactions). 1. Light Reaction or Light Dependent Reaction Light Produces energy from solar power energy solar (photons) in the form of ATP and NADPH. (photons) ATP NADPH Breakdown of Photosynthesis Breakdown 2. Calvin Cycle or Light Independent Reaction or Carbon Fixation or C Fixation 1. Light Reaction (Electron Flow) 1. • Occurs in the Thylakoid membranes Thylakoid • During the light reaction, there are two light possible routes for electron flow. possible electron A. Cyclic Electron Flow B. Noncyclic Electron Flow A. Cyclic Electron Flow A. • • • • • Occurs in the thylakoid membrane. thylakoid Uses Photosystem I only Photosystem P700 reaction center- chlorophyll a Uses Electron Transport Chain (ETC) Electron Generates ATP only ADP + P ATP ATP A. Cyclic Electron Flow A. SUN Primary Electron Acceptor eeeATP produced by ETC ePhotons P700 Accessory Pigments Photosystem I B. Noncyclic Electron Flow B. • Occurs in the thylakoid membrane thylakoid • Uses PS II and PS I PS PS • P680 rxn center (PSII) - chlorophyll a • P700 rxn center (PS I) - chlorophyll a • Uses Electron Transport Chain (ETC) Electron • Generates O2, ATP and NADPH B. Noncyclic Electron Flow B. 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 B. • ADP + P (Reduced) → → ATP ATP NADPH NADPH • NADP+ + H (Reduced) • Oxygen comes from the splitting of Oxygen H2O, not CO2 not CO H2O → (Oxidized) 1/2 O2 + 2H+ Chemiosmosis Chemiosmosis • Powers ATP synthesis. ATP • Located in the thylakoid membranes. thylakoid • Uses ETC and ATP synthase (enzyme) to (enzyme) make ATP. • Photophosphorylation: addition of phosphate to ADP to make ATP. phosphate ADP ATP Chemiosmosis 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 Chloroplast Stroma Outer Membrane Inner Membrane Thylakoid Granum Calvin Cycle (C3 fixation) Calvin (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 Calvin • Remember: C3 = Calvin Cycle C3 C3 Glucose Photorespiration Photorespiration • Occurs on hot, dry, bright days. hot, • Stomates close. • Fixation of O instead of CO . • Produces 2-C molecules instead of 3-C 2-C sugar molecules. sugar • Produces no sugar molecules or no ATP. 2 2 Photorespiration Photorespiration • Because of photorespiration: Plants have Plants special adaptations to limit the effect of special photorespiration. photorespiration 1. C4 plants 2. CAM plants C4 Plants C4 • Hot, moist environments. • 15% of plants (grasses, corn, sugarcane). • Divides photosynthesis spatially. • Light rxn - mesophyll cells. • Calvin cycle - bundle sheath cells. C4 Plants C4 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 CAM • Hot, dry environments. • 5% of plants (cactus and ice plants). • Stomates closed during day. Stomates closed • Stomates open during the night. Stomates open • Light rxn - occurs during the day. • Calvin Cycle - occurs when CO2 is present. CAM Plants CAM 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: Question: • Why would CAM plants close their Why stomates during the day? stomates Photosynthesis Photosynthesis is a process which light energy is used in the synthesis of organic molecules. What is the equation for photosynthesis? Water + carbon dioxide +light energy = Oxygen + glucose The role of chloroplasts in Photosynthesis. • Chloroplast is an organelle in the leaf of a plant that contain the thylakoid cells and the stroma. These are shown on the following diagram. • Here 2 important reactions take place. The light dependant reactions take place in the thylakoid cells and the light independent in the stroma. Chloroplasts What happens in the light dependent reactions. • Electrons in the chloroplast gain energy from sunlight , this energy is used to add a phosphate group to ADP making ATP. • The energy is used also used in the photolysis of water to split it into oxygen and hydrogen molecules • The electrons, protons and energy for the light dependent reactions are used to make NaDPH2. • The ATP/NADPH2 from the Light Dependent reactions enter the light independent reactions. What happens in the light independent reactions. The light independent reactions occur at night for only a few seconds due to limited amounts of ATP and supply of NADPH2. Role of NADPH2 and ATP Energy from ATP and electrons from NADPH2 are used to reduce carbon dioxide and build it to sugars The following cycle is called the Calvin cycle. • This is called Fixing the carbon dioxide. The carbohydrates(sugars) are in a form of RuBP. • The following cycle is called the Calvin cycle. • What happens in the Calvin cycle? • RuBP with the addition of carbon dioxide splits into 2 moles of GP. For GP to be turned to Carbohydrates it requires ATP and NADPH2. The NADPH2 give up its electrons which enter the GP molecules making GALP. GALP GALP is converted to a whole series of mostly sugars, some lipids and some Proteins. • Also some GALP is regenerated back to RUBP if sufficient amounts of NADPH2 and ATP are provided. Photosynthesis Photosynthesis H 2O + Energy ATP and NADPH2 CO 2 Which splits water Light is Adsorbed By By Chlorophyll Chlorophyll C3 ADP NADP Calvin Cycle Chloroplast Used Energy and is Used recycled. recycled. O2 L ight Reaction + C 6H 12O 6 D ar k Reaction ...
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