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How Cells Acquire Energy Chapter 6 Carbon and Energy Sources ____________- Plants, some bacteria, many protistans – Carbon source is _______________ – Energy source is ___________ _______________ – Get carbon and energy by eating __________ or _______________ T.E. Englemann’s Experiment Background – Certain bacterial cells will move toward places where oxygen concentration is high – Photosynthesis produces oxygen Hypothesis – Movement of bacteria can be used to determine optimal light wavelengths for photosynthesis Method – Algal strand placed on microscope slide and illuminated by light of varying wavelengths – Oxygen-requiring bacteria placed on same slide Results • Bacteria congregated where red and violet wavelengths illuminated alga Conclusion Bacteria moved to most effective light for photosynthesis Linked Processes ______________ • Energy-storing pathway • Releases _______ • Requires ______ ________ _______________ • Energy-releasing pathway • Requires _______ • Releases carbon dioxide LIGHT ENERGY ____ + _____ water carbon dioxide ___ + _____ + _____ oxygen glucose water Visible Light • Wavelengths humans perceive as different ______ • Violet (___ nm) to red (____ nm) • Longer wavelengths, lower energy shortest longest Of the energy that reaches Earth’s surface, about ___ is intercepted by photoautotrophs Photons • Packets of ______ energy • Photons with most energy travel as ________ wavelength (blue-green light) Pigments • Light-absorbing ________ • Absorb some wavelengths and ________ others • Color you see are the wavelengths ___ absorbed chlorophyll a chlorophyll b Wavelength (nanometers) Plants contain 4 main pigments • _______________- reflect green- most common • ___________- reflect red/yellow – Includes xanthophiles and carotenes • ______________- give flowers their colors • __________- in red algae •In bacteria- pigments are in ____________ •In plants- pigments are in _________ _____________ of chloroplasts 2 Photosystems and Electron Transporters water-splitting complex H2O thylakoid compartment 2H + 1/2O2 P680 P700 acceptor acceptor PHOTOSYSTEM II pool of electron transporters stroma PHOTOSYSTEM I Two _______ of Photosynthesis sunlight water uptake carbon dioxide uptake ATP 1. ________ _________________ ADP + Pi 2. _______ _____________ NADPH NADP+ P • Pigments absorb ____ energy oxygen release • _____split • ___ and _____ formed • _______ released glucose •CO2 converted tonew _____ water •Can proceed in the _____ •___________ cycle 1. LIGHT DEPENDENT-REACTIONS Many _______ capture energy… ….but all energy is funneled into ______ _______ reaction center (a specialized chlorophyll a molecule) Then an electron is sent to the ________ 1. LIGHT DEPENDENT-REACTIONS In ET system, ATP is produced electron acceptor e– electron transport system e– e– ATP e– In ET system: 1. LIGHT DEPENDENT-REACTIONS • two photosystems: ______ and ______ H2O photolysis e– e– NADP+ PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE NADPH ADP + Pi End result• _______regenerated • ____ is concentrated inside • _____ made when H+ is moved across membrane ATP 6 CalvinBenson Cycle CO2 ATP NADPH _________ ______ ________ CO2 (from the air) CARBON FIXATION 6 6 RuBP unstable intermediate 12 PGA 6 ADP 6 12 ATP ATP 12 NADPH 4 Pi P-glucose 12 ADP 12 Pi 12NADP+ 10 PGAL 12 PGAL 2 PGAL _______ _______ Pi P glucose Alternative mechanisms of carbon fixation have evolved in hot, arid climates • The _______ are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporative loss of _______. • On hot, dry days plants close the stomata to conserve water, but this causes problems for photosynthesis. Solution # 1 C3 plants- •____________- fix ___ (Not CO2) •But photorespiration can drain away as much as _____ of the carbon fixed by the Calvin cycle Solution # 2 Solution # 3 __________ CO2 ___________ e.g. pineapple e.g. sugarcane CO2 In mesophyll cell, stomata open at night; CO2 uptake but no water loss in mesophyll cell, oxaloacetate cell carbon fixation CALVINBENSON CYCLE in bundle-sheath cell, carbon fixed again more CO2in leaf, no photorespiration Fix CO2 as other ____________, then use as needed CALVINBENSON CYCLE Stomata close during day; CO2 that accumulated in leaf overnight is used Fix CO2 as other molecules at _____, then use during ____ Summary of Photosynthesis light 12H2O LIGHT-DEPENDENT REACTIONS 2 ADP + ATP Pi 6CO2 6O NADP+ NADPH PGA CALVIN- PGAL BENSON CYCLE RuBP P C6H12O 6 (phosphorylated glucose) end product (e.g. sucrose, starch, cellulose)