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Photosynthesis • An anabolic, endergonic, carbon dioxide (CO2) requiring process that uses light energy (photons) and water (H2O) to produce organic macromolecules (glucose). SUN photons 6CO2 6O2 + 6H2O C6H12O6 + glucose •Where does photosynthesis take place? Plants • Autotrophs: self-producers. • 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 Water (H2O) Mesophyll Cell Cell Wall Central Vacuole Nucleus Chloroplast Chloroplast • Organelle where photosynthesis takes place. Stroma Outer Membrane Inner Membrane Thylakoid Granum Thylakoid Thylakoid Membrane Granum Thylakoid Space •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 red-660 nm are most important). • Plants are green because the green wavelength is reflected, not absorbed. Wavelength of Light (nm) 400 Short wave (more energy) 500 600 700 Long wave (less energy) Absorption of Chlorophyll Absorption violet blue green yellow wavelength orange red •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. Other pigments of photosynthesis include Other chlorophylls, xanthophylls, carotenoids, fucoxanthins, anthocyanins, tannins 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 The Source of Oxygen Produced by Photosynthesis 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 C3 Fixation Uses energy (ATP and NADPH) from light rxn to make sugar (glucose). 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 Primary Electron Acceptor SUN e- e- ePhotons P700 Accessory Pigments Photosystem I e- ATP produced by ETC 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 SUN 2e- 2e- Photon H2O 1/2O2 + 2H+ Enzyme Reaction 2e- ETC 2e- 2e- P700 NADPH ATP P680 Photosystem II Photon Photosystem I B. Noncyclic Electron Flow • ADP + P ATP (Reduced ) • NADP+ + H NADPH (Reduced) • Oxygen comes from the splitting of H2O, not CO2 H2O (Oxidized) 1/2 O2 + 2H+ 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+ Thylakoid (Proton Pumping) E T PS II PS I C H+ H+ H+ H+ H+ H+ ADP + P H+ H+ high H+ concentration ATP Synthase ATP Thylakoid Space 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) (36C) 6C-C-C-C-C-C (6C) 6CO2 (unstable) (30C) 6C-C-C-C-C RuBP (30C) glucose 6C-C-C 12PGA (36C) 6ATP 6ATP 6NADPH 6NADPH 6C-C-C 6ATP C3 6C-C-C (36C) 6C-C-C 12G3P (6C) C-C-C-C-C-C Glucose Calvin Cycle • Remember: C3 = Calvin Cycle C3 Glucose Tracing the Pathway of CO2 Photorespiration/Calvin-Benson Cycle • Occurs on hot, dry, bright days. • Stomates close. • Fixation of O2 instead of CO2. • Produces 2-C molecules instead of 3-C sugar molecules. • Produces no sugar molecules or no ATP. 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 Pathway PEP (phosphoenolpyruvate) + CO2 4C (oxaloacetic acid) using enzyme PEP carboxylase PEP carboxylase has a higher affinity for CO2 than RuBP carboxylase Ocaloacetic acid + NADPH malic acid Malic acid CO2 + pyruvic acid CO2 enters C3 pathway C4 Plants Malate C-C-C-C Malate C-C-C-C Transported CO2 CO2 C3 glucose C-C-C PEP ATP Mesophyll Cell C-C-C Pyruvic Acid Bundle Sheath Cell Vascular Tissue 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 Pathway • CO2 is captured at night and stored in vacuoles of mesophyll cells is then • CO2 is then converted to crassulacean acid • IN the morning, crassulacean acid is converted back to CO2 and can enter the C3 pathway • Stomata close during the day • Found in cacti & succulents 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? • Okay, let’s try this one more time… Calvin Cycle/ Pathway C3 C4 Pathway CAM (Crassulacean Acid Metabolism) CO2 crassulacean acid CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase CO2+PEPoxaloacetic acid (4C) Enzyme=PEP carboxylase Occurs in mesophyll Oxaloacetid acid + NADPHP Malic acid CO2 + pyruvic acid Occurs in bundle sheath cells CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase DPGA + 2NADPH2PGAL DPGA + 2NADPH2PGAL DPGA + 2NADPH2PGAL Stomata opened Stomata close reduce H2O loss Rice, wheat, soybeans, cotton, tomatoes, Crabgrass, pineapple RibuloseRuBP partially sugarcane to corn, CO2 stored in vacuoles of mesophyll cells crassulacean acid CO2 CO2 + RuBPDPGA (3C) Enzyme=RuBP carboxylase Stomata close during the day Cacti & succulents Resources • • • • • Photosynthesis Tutorial Plant Metabolism Photosynthesis Problem Set DNA Tube How Do Proteins Help Chlorophyll Carry Out Photosynthesis? Virtual Lab • Calvin Cycle Tutorial • Photosynthesis Animation • Transpiration Virtual Plant Lab