Photosynthesis: The Process of Converting Light Energy into Chemical Energy, Slides of Biology

Download Photosynthesis: The Process of Converting Light Energy into Chemical Energy and more Slides Biology in PDF only on Docsity! Photosynthesis: Capturing Energy Chapter 9 docsity.com Light Consists of particles (photons) that move as waves Photons with shorter wavelengths have more energy than those with longer wavelengths docsity.com Photosynthetic Pigments • In thylakoid membranes – chlorophyll a – chlorophyll b – Carotenoids docsity.com Energizing Electrons • chlorophyll Photons excite photosynthetic pigments • move to electron acceptor compounds Energized electrons docsity.com Active Wavelengths • Combined absorption spectra of chlorophylls a and b – action spectrum for photosynthesis docsity.com The Photosystems Photosystems I and II photosynthetic units include chlorophyll, accessory pigments organized with pigment-binding proteins into antenna complexe docsity.com A Photosystem Primary electron acceptor Thylakoid membrane Photosystem © 2007 Thomson Higher Education docsity.com LIsNt-aqepenaent reactions Primary electron SeeePn Electron transport chain Electron transport Production of ATP by chemiosmosis 0.5 Photosystem | (P70) Oxidation-reduction potential (volts) (relative energy level) 15 @ Electrons are supplied to system from the splitting of HO by photo- — @ Electrons in photosystem | are “re-energized” system Il, with release of O as by-product. When photosystem Il is by absorption of additional light energy and activated by absorbing photons, electrons are passed along electron are passed to NADP", forming NADPH. transport chain and are eventually donated to photosystem I. © 2007 Thomson Higher Education docsity.com Cyclic Electron Transport • Electrons from photosystem I – return to photosystem I • ATP produced by chemiosmosis • No NADPH or oxygen generated docsity.com TABLE 9-1 A Comparison of Noncyclic and Cyclic Electron Transport Electron source Oxygen released? Terminal electron acceptor Form in which energy is temporarily captured Photosystem(s) Cy : : . " 17 Thomson Higher Education Noncyclic Electron Transport H,0 Yes (from HO) NADP* ATP (by chemiosmoasis); NADPH PS | (P700) and PS II (P680) Cyclic Electron Transport None—electrons cycle through the system No None—electrons cycle through the system ATP (by chemiosmosis) PS | (P700) only docsity.com Proton Gradient * Stroma °° - . Thylakoid lumen Thylakoid membrane/ , * Protons (H*) © 2007 Thomson Higher Education docsity.com Calvin Cycle (C3 pathway) Carbon fixation reactions 3 phases • CO2 uptake (fixation) phase • Carbon reduction phase • RuBP regeneration phase docsity.com CO2 Fixation Phase Enzyme rubisco (ribulose bisphosphate carboxylase/ oxygenase) combines CO2 with ribulose bisphosphate (RuBP), a five-carbon sugar forms 3-carbon phosphoglycerate (PGA) docsity.com Carbon Reduction Phase Energy of ATP and NADPH convert PGA molecules to glyceraldehyde-3- phosphate (G3P) J 7 For each 6 CO, fixed 2 G3P leave cycle to produce 1 glucose ® docsity.com 12 G3P are produced Photorespiration C3 plants use O2 and generate CO2 • by degrading Calvin cycle intermediates • but do not produce ATP On bright, hot, dry days • plants close stomata, conserving water • prevents passage of CO2 into leaf docsity.com C4 Pathway • Takes place in mesophyll cells • Enzyme PEP carboxylase binds CO2 • CO2 fixed in oxaloacetate – converted to malate • Malate moves into bundle sheath cell – CO2 is removed • Released CO2 enters Calvin cycle docsity.com C, and C, Plants —— . Upper =— ’ i ~ iis ; epidermis : » Palisade mesophyll Bundle sheath cells of veins (a) In C3 plants, the Calvin cycle takes place in the mesophyll (b) In Cy plants, reactions that fix CO into four-carbon compounds cells and the bundle sheath cells are nonphotosynthetic. take place in the mesophyll cells. The four-carbon compounds are transferred from the mesophyll cells to the photosynthetic bundle sheath cells, where the Calvin cycle takes place. © 2007 Thomson Higher Education e docsity.com