1Lec 10. Plants provide the primary organic food for all living organisms.Plants provide oxygen in the atmosphere, fossil fuel, fiber.How do plants convert CO2and NO3-to organic food? Carbohydrates, proteins, lipids, secondary products (medicine)Lec. 10. Photosynthesis 1I. Overview of Photosynthesis: 4 STAGES:1. Light Absorption: Electrons are pulled from water, and O2is evolved. (LIGHT RX)2. Electron Transport : NADPH is formed. (LIGHT RX)3. Generation of ATP. (LIGHT RX)4. Conversion of CO2into Carbohydrates. (DARK RX) II. Chloroplast & PigmentsIII. Light Absorption by PigmentsHow is light absorbed? What does absorbed light do?Light energy absorbed by pigments is transferred to a reaction center Chl a. Rx center chl a gives up an electron. Photooxidation or photochemistryChl a pulls electrons from water generating oxygen.This reaction is the key to photosynthesis. This reaction starts electron transport.Overview of photosynthesis1. Light absorptionwater is split2. NADPH Reducing energy is formed3. ATPChemical energy is formed4. CO2-->--> sugarCO2is converted to sugarsDiscovery of PS1. Van Helmont. Water was the main nutrient2. Stephen Hales: Air supplied the nutrient3. Priestley 1770s. Light caused plants to evolve something that supported a burning candle4. Ingenhousz 1779. Plants evolved oxygen.Only green parts evolved O2.SpirogyraGreen algae21-4TaizLeaves are the photosynthetic organs of land plantsStructure and Formation of the chloroplast:Plastid differentiation-7-15. EM of a chloroplastStromathylakoidChloroplast7-16. TaizChlorophylls & other pigments7-6 Taiz. PS pigmentsQ? Is chl soluble in water or ethanol?Functions:1. Anti-oxidants2. Absorb blue light for PS37-20 Taiz: Pigments bind to protein to form a Light Harvesting ComplexLHCPA complex can consist of 250-300 Chl.7-18 Taiz. Protein complexes on the thylakoid membranePlants use the energy of visible lightHow is light absorbed and used for photochemistry?13. Farabee. Light has properties of a Wave and a particle. E = h νChlorophyll absorbs in the blue and red1. Principle of Gotthaus-DraperOnly light that is absorbed can be active in a photochemical reaction.2. Einstein-Stark Law.A single photon can excite only one electron.1. Amount of energy is dependent on the wavelength of light.Light has properties of a wave and a particle (photon). Quantum (energy of a photon) = hν = hc/λ2. Plants contain pigments that absorb the energy of photons. When molecules absorb light, they change their electronic stateBasic Concepts about Light13. Farabee. Absorption spectra of pigments7-7. Taiz4Chlorophyll can absorb a photon, -get excited and -give up a high energy electronWhat is light absorbed used for?a) excitation energy transferb) photochemistry or photo-oxidationThis is the beginning of photosynthesis7-5 Taiz. Light absorption and emission by chlorophyll7-19 Light-harvesting antenna: energy is funneled to the reaction center chl. Bulk of Chl are antenna chl.7-10. Taiz. Energy transferSummary:Chl and accessory pigments absorb light energy.Energy absorbed is funneled by excitation energy transfer to a special chl a pair (Reaction Center pigment)At RC, chl a is oxidizedOxidation results in chl a pulling e- from H2O generating oxygen.?? Rx ?7-9. Concept of Action SpectrumWhat wavelength of light is effective in