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2/6/2011 Investigating Photosynthesis Essentials of Biology Sylvia S. Mader One of the first questions…. • When a tiny seedling grows into a tall tree with a mass of several tons, where does all that mass come from? Chapter 6 Photosynthesis Lecture Outline Chandelier Tree • • 315 ft. high and 21 ft. in diameter Giant Redwood tree at Drive Thru Tree Part, Leggett, CA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2. ___________ Experiment (1771) Priestly’s Van Helmont’s Experiment (1643) 1. ______________ Put soil in pot and took mass Took a seedling and took mass Put seed in soil...watered...waited five years... the seedling became a tree. Mass of soil barely changed. He concluded that the mass came from water He determined the the ―hydrate‖ in the carbohydrate portion of photosynthesis Jan Ingenhousz 3. ________________Experiment (1779) Put aquatic plants in light... produced oxygen Put aquatic plants in dark... No oxygen Put a lit candle in a bell jar and… The flame died out. Placed a mint plant in the jar with the candle and … Flame lasted longer Concluded… plants release a substance needed for a candle to burn He determined that plants release… oxygen 6.1 Overview of Photosynthesis • • He determined: Light is needed to produce oxygen • • PSN occurs in plants, algae, some protists and some prokaryotes Why is PSN the most important chemical process on earth? Provides food nearly all organisms Transforms solar energy into chemical energy of carbohydrates. Melvin Calvin 4. _______________ (1948) He determines carbon’s path to make glucose Known as the Calvin’s cycle Figure 6.1 1 2/6/2011 Flowering plants Photosynthesis Overview • Green portions carry on photosynthesis. • CO2 enters & O2 exits leaves through stomata. • Roots absorb water. • Autotrophs (“self feeders”) PSN is the process by which autotrophs use light energy to make sugar and oxygen gas from carbon dioxide and water • CO2 and H2O diffuse into mesophyll cells and then into chloroplasts. Figure 6.2a • An overview of photosynthesis H 2O Figure 6.3 CO2 Chloroplast NADP+ ADP + P CALVIN CYCLE (in stroma) Two sets of reactions • Light reactions ATP, NADPH & O2 produced H and O2 come from H2O • Calvin cycle reactions Occur in stroma ATP CO2 taken up ATP and NADPH used to reduce CO2 to produce carbohydrate NADPH O2 Figure 6.3 Occur in thylakoid membrane Chlorophyll absorbs solar Light LIGHT REACTIONS (in grana) Photosynthesis Overview Sugar BioFlix: Photosynthesis Photosynthetic process Begins with the end products of cellular respiration: CO2 and H2O Hydrogen atoms removed from water are added to carbon dioxide. • Solar energy is required. O2 is a byproduct of the oxidation of water. End product is CH2O or glucose C6H12O6. 6.2 Light Reactions • Leaf pigments absorb solar energy. • Light travels as waves Shorter wavelengths contain more energy. Longer wavelengths contain less energy. • Vision and photosynthesis are adapted to use visible light Figure 6.4 Page 88 2 2/6/2011 Figure 6.5 What determines the color of a leaf? • Electron pathway of light reactions Capture sun’s energy and stores in the form of a hydrogen ion (H+) gradient • Gradient used to produce ATP NADPH is also produced. • What colors of light does a green leaf absorb? Color(s) reflected? • Why do leaves change color? • Chlorophyll covers up other pigments that are always present e.g. Carotenoids (orange); xanthophylls (red) The Interdependence of the Light Reactions & the Calvin Cycle H2O CO2 ADP + P Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. NADP+ Calvin cycle reactions Light reactions NADPH ATP Figure 6.6 O2 CH2O (carbohydrate) A mechanical analogy for the light reactions The Steps of the Light Reactions e– ATP Electron acceptor e– e– Electron acceptor NADPH e– e– Mill makes ATP Light Energy Light Energy e– Energy for synthesis of e– PHOTOSYSTEM I PHOTOSYSTEM II Figure 6.6 Photosystem 2 Photosystem 1 3 2/6/2011 chloroplast Making ATP, NADPH & O2 with Sunlight (Low H+) Light Light Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Figure 6.7 (High H+) Steps of the Light Reactions • Photosystem II 6.3 The Calvin Cycle Solar energy energizes electrons. Electrons escape to electron acceptor molecule. • Sent through electrons transport chain Replacement electrons obtained by splitting water • Releases oxygen gas as waste product Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. • Electron Transport Chain Series of carriers pass electrons along releasing energy. Energy stored in form of H+ gradient Will be used to make ATP • Photosystem I Solar energy energizes electrons. Electrons captured by another electron acceptor molecule Electrons and a hydrogen passed to NADP+ to become NADPH Replacement electrons come from electron transport chain. 6.3 Calvin Cycle Reactions H2O CO2 ADP + 1. • • • • Powered by __???__ and __???__ produced by the light reactions Occurs in the __???__ of the chloroplast End product is __???__ 3 steps 1. 2. 3. Carbon Dioxide Fixation P NADP+ Calvin cycle reactions Ligh reactionst NADPH ATP 3 CO2 O2 Unstable C6 Intermediate CH2O stroma (carbohydrate) 3 C6 3 RuBP Rubisco CO2 fixation Calvin cycle reactions CO2 fixation CO2 reduction Regeneration of first substrate , RuBP CO2 from the atmosphere attached to RuBP by RuBP carboxylase (rubisco) 6 carbon molecule split into two 3 carbon molecules. 6 3PG CO2 reduction Regeneration of RuBP Key molecules of the Calvin Cycle RuBP ribulose 1,5-bisphosphate Figure 6.8 3PG 3-phosphoglycerate BPG 1,3-bisphosphoglycerate G3P glyceraldehyde-3-phosphate 4 2/6/2011 H2O 2. CO2 ADP + Reduction of Carbon dioxide P NADP+ Uses NADPH (for H) and some ATP (for energy) from light reactions G3P reacts to produce glucose & other organic molecules Calvin cycle reactions Ligh reactionst NADPH ATP 3 CO2 O2 intermediate stroma CH2O (carbohydrate) 3 C6 H2O CO2 3. NADP+ Calvin cycle reactions Ligh reactionst NADPH ATP 3 CO2 O2 intermediate stroma CH2O (carbohydrate) 3 C6 3 RuBP 3 RuBP 6 3PG CO2 fixation Calvin cycle reactions CO2 reduction 6 3PG CO2 fixation 6 ATP From light reactions 3 ADP + 3 P 6 ADP + 6 P Regeneration of RuBP Calvin cycle reactions From light reactions 3 ATP 6 BPG 6 ATP CO2 reduction Regeneration of RuBP 6 NADP+ Glucose and other organic molecules 6 BPG From light reactions 5 G3P Key molecules of the Calvin Cycle 6 G3P 6 NADP+ 3-phosphoglycerate BPG 1,3-bisphosphoglycerate G3P glyceraldehyde-3-phosphate • Plants and algae can make any molecule they need from G3P! Figure 6.8 amino acids glycerol fatty acids G3P glucose phosphate cellulose Nucleotides for DNA and RNA Sucrose for transport through plant Starch for storage Key molecules of the Calvin Cycle RuBP ribulose 1,5-bisphosphate Net gain of one G3P 3PG starch Glucose and other organic molecules 3PG 3-phosphoglycerate BPG 1,3-bisphosphoglycerate G3P glyceraldehyde-3-phosphate 6.4 Other types of Photosynthesis Why is G3P possibly the most important molecule for life? Amino acids Fatty acid and glycerol Glucose for energy needs Uses ATP from light reactions 6 ADP + 6 P RuBP ribulose 1,5-bisphosphate Net gain of one G3P One G3P made into glucose or other organic molecules. 5 G3P used to reform RuBP (5 carbon molecule) 6 NADPH From light reactions 6 G3P From light reactions 6 NADPH Figure 6.8 Regeneration of RuBP P ADP + • Plants are adapted to their climate • When temperature and rainfall are moderate Use C3 photosynthesis C3 plants • C3 compound formed first after CO2 fixation sucrose Cellulose for cell walls Figure 6.9 The fate of G3P C3 plants in Hot and Dry Weather Figure 6.10 Carbon fixation in C3 plants day • Water loss can be deadly! • Close stomata to prevent water loss CO2 mesophyll cell RuBP Calvin cycle G3P CO2 fixation in a C3 plant, blue columbine C3 Limits water loss, but… CO2 intake stops O2 builds up; results in photorespiration • Photorespiration—a farmer’s worst enemy! Rubisco uses O2 instead of CO2 Destroys RuBP Limits growth in C3 plants Common C3 Plants wheat, rice, barley, potatoes, sugar beet, soybeans, many grasses 5 2/6/2011 Figure 6.11 Comparison of C3 and C4 plant anatomy Carbon dioxide fixation in C4 plants Daytime • C4 compound formed after 1st CO2 fixation • Partitioning of pathways in space • Mesophyll cells shield bundle sheath cells from buildup of O2. • Chloroplasts in bundle sheath cells carry out Calvin cycle only. • Common C4 Plants Corn, sorghum, millet, and sugarcane C4 plant C3 plant • Calvin cycle and light reactions both in Mesophyll cells An advantage in cool, wet weather • C4 plants partition reactions • Avoids O2 exposure to Rubisco • Allows stomata to stay closed (conserving water) • Advantage in hot dry weather Figure 6.12 CAM photosynthesis Crassulacean acid metabolism Most succulents in a desert environment Partitioning in time CAM plants open stomata at night when it is cooler. Use C3 molecules to fix CO2 forming C4 molecules Figure 6.13 night Carbon dioxide fixation in a CAM plant CO2 C4 CO2 • Store C4 molecules in vacuoles Calvin cycle Close stomata during the day to avoid water loss Release stored CO2 when NADPH and ATP available from light reaction G3P day CO2 fixation in a CAM Plant, Pineapple • Evolutionary trends C4 plants most likely evolved in, and are adapted to, areas of high light, high temperature, and limited rainfall. • More sensitive to cold – C3 plants do better than C4 plants below 25°C CAM plants compete well with C3 or C4 when the environment is extremely arid. • CAM is quite widespread 6