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PHOTOSYNTHESIS Photosynthesis: Life from Light and Air CAPTURING THE ENERGY IN LIGHT The process by which organisms obtain energy directly from sunlight is called photosynthesis. CO2 + H2O → C6H12O6 + O2 ENERGY FOR LIFE PROCESSES Autotrophs: most Plants, Algae, and some Bacteria. Autotrophs store energy in various organic compounds, primarily carbohydrates. The Basic By McGraw Hill Photosynthesis involves a complex series of chemical reactions: Biochemical Pathway Products used in cellular respiration in both plants and animals. Redox Reactions: OIL RIG Oxidation is Loss Reduction is Gain (of e-) or Oxidation is loss of hydrogen. Reduction is gain of hydrogen. How are they connected? Heterotroph and…. glucose + oxygen carbon + water + energy dioxide C6H12O6 + 6O2 6CO2 + 6H2O + ATP oxidation = exergonic carbon + water + energy glucose + oxygen dioxide 6CO2 + 6H2O + light C6H12O6 + 6O2 energy Autotroph reduction = endergonic What does it mean to be a plant Need to… collect light energy glucose transform it into chemical energy store light energy in a stable form to be moved around the plant or stored need to get building block atoms from the environment ATP C,H,O,N,P,K,S,Mg produce all organic molecules needed for growth carbohydrates, proteins, lipids, nucleic acids CO2 N K P … H2O LIGHT ABSORPTION IN CHLOROPLASTS Light Reactions or Light Dependent Reactions They begin with the absorption of light in chloroplasts. Review of the Light Reaction With All Details! CHLOROPLASTS LIGHT AND PIGMENTS chlorophylls accessory pigments carotenoids Photosynthesis gets energy by absorbing wavelengths of light. Accessory pigments with different structures absorb light of different wavelengths: chlorophyll a & b, carotenoids, xanthophylls, antenna pigments What is Photosynthesis? Light reactions light-dependent reactions convert solar energy to chemical energy ATP & NADPH Calvin cycle light-independent reactions sugar building reactions uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6 It’s not the Dark Reactions! Virtual Cell Photo. LIGHT REACTIONS ELECTRON TRANSPORT CHAIN: PHOTOSYSTEMS II AND I. 1. 1. 2. 3. chlorophyll a P680 = absorbs 680nm wavelength red light chlorophyll b P700 = absorbs 700nm wavelength red light Photosystem I REPLENISHING PHOTOSYSTEM II CHEMIOSMOSIS Go to: D-Drive Virtual Cell:Photosynthesis Youtube Streaming Video Photosystem I file b ELECTRON TRANSPORT CHAIN The Basic Biochemical Pathway RESTORING PHOTOSYSTEM II CHEMIOSMOSIS What is Photophosphorylation? cyclic photophosphorylation NADP NONcyclic photophosphorylation ATP Why Cyclic Phosphorolation? Calvin cycle uses more ATP than NADPH 18 ATP + 12 NADPH 1 C6H12O6 PUTTING IT ALL TOGETHER Overview Of the Light Reaction Review of the Light Reaction With All Details! Photosynthesis Animation http://www.stolaf.edu/people/giannini/flashani mat/metabolism/photosynthesis.swf Experimental evidence Where did the O2 come from? radioactive tracer = O18 Experiment 1 6CO2 + 6H2O + light C6H12O6 + 6O2 energy Experiment 2 6CO2 + 6H2O + light C6H12O6 + 6O2 energy Proved O2 came from H2O not CO2 = plants split H2O! Photosynthesis summary Where did the energy come from? Where did the electrons come from? Where did the H2O come from? Where did the O2 come from? Where did the O2 go? Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for? So where does CO2 fit in? How do plants use it? Why do they need it? LIGHT INDEPENDENT to the Dark REACTIONS Welcome Side, Lord Calvin KNOWN AS THE CALVIN CYCLE = C3 Photosynthesis. do CO2 IS FIXED INTO ORGANIC How Plants Capture COMPOUNDS: CARBON CO2? FIXATION. THREE MAJOR STEPS, WHICH OCCUR WITHIN THE STROMA. Calvin Reduction Reaction= C gains H+ Cycle P.S. The Dark Cycle Does Not Happen in the Dark It is dependent on the products of the light reaction (ATP and NADPH) So when the lights go out…it has no energy to continue. NOVA Capturing C Think… Why can’t we blow carbon emissions into forests and solve global warming? ALTERNATIVE PATHWAYS TO FIX CARBON These alternative pathways are generally found in plants that evolved in hot, dry climates. Stomata: passageways FOR CO2 and O2. C-4: Photosynthesis Intense Sunlight and Hot (e.g. corn and crabgrass) Stomata are Partly Closed During Day= CO2 falls and O2 rises We don’t want photorespiration. In the Mesophyll PEP carboxylase grabs CO2 not O2. Sends CO2 to the Calvin cycle The C4 Pathway FIXES CO2 INTO A FOUR CARBON COMPOUND OXALOACETATE. HENSE THE NAME: C4 Oxaloacetate in the mesophyll turns into Malate, an acid. Malate is shipped through plasmodesmata into bundle sheath cells and release CO2 Calvin Cycle Starts The CAM Plants Crassulacean Acid Metabolism Adaptation to Dry Conditions Stomata Closed during Day Open at Night Mesophyll stores CO2 at night Makes Sugar during Day All 3 (C3, C-4, and CAM) use the Calvin Cycle The CAM Pathway Plants that use the CAM pathway open their stomata at night and close them during the day—just the opposite of what other plants do. RATE OF PHOTOSYNTHESIS Review