Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vascular bundleStoma Cuticle Epidermis Mesophyll Chloroplast Inner membrane Outer membrane Cell wall 1.58  m Vacuole Courtesy Dr. Kenneth Miller, Brown University 1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O2O2 Stroma Photosystem Thylakoid NADP + ADP + P i CO 2 Sunlight Photosystem Light-Dependent Reactions Calvin Cycle Organic molecules O2O2 ATP NADPH H2OH2O 2

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 400 nm Visible light 430 nm500 nm560 nm600 nm650 nm740 nm 1 nm0.001 nm10 nm1000 nm Increasing wavelength Increasing energy 0.01 cm1 cm1 m Radio wavesInfraredX-raysGamma rays 100 m UV light 3

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Wavelength (nm) Light Absorbtion low high carotenoids chlorophyll a chlorophyll b 4

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2CH2CCH CH 2 CH 3 H H H C O CH CCH 3 CHCH 3 CH 2 CHCH 3 CH 2 CHCH 3 CH 3 O CO 2 CH 3 O NN NN Mg H H Chlorophyll a: = CH 3 Chlorophyll b: = CHO R R R H Porphyrin head H3CH3C H3CH3C CH 3 CH 2 Hydrocarbon tail 5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oak leaf in summer Oak leaf in autumn © Eric Soder 6

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. e–e– Photon Photosystem Thylakoid membrane Chlorophyll molecule Electron acceptor Reaction center chlorophyll Thylakoid membrane Electron donor e–e– 7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Light e–e– – + –+ Excited chlorophyll molecule Electron donor Electron acceptor Chlorophyll reduced Chlorophyll oxidized Donor oxidized Acceptor reduced e–e– e–e– e–e– e–e– e–e– e–e– e–e– 8

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy of electrons e–e– Photon Excited reaction center Plastoquinone Plastocyanin Ferredoxin Photosystem II Photosystem I Photon b 6 -f complex 2. The electrons pass through the b 6 -f complex, which uses the energy released to pump protons across the thylakoid membrane. The proton gradient is used to produce ATP by chemiosmosis. 3. A pair of chlorophylls in the reaction center absorb two photons. This excites two electrons that are passed to NADP +, reducing it to NADPH. Electron transport from photosystem II replaces these electrons. H2OH2O H+H+ PC Fd 2H / 2 O 2 NADP + + H + NADPH A pair of chlorophylls in the reaction center absorb two photons of light. This excites two electrons that are transferred to plastoquinone (PQ). Loss of electrons from the reaction center produces an oxidation potential capable of oxidizing water. Reaction center Proton gradient formed for ATP synthesis Reaction center NADP reductase e–e– e–e– e–e– e–e– PQ 9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Photosystem IIPhotosystem Ib 6 -f complex Stroma Plastoquinone Proton gradient PlastocyaninFerredoxin H+H+ H+H+ H+H+ H+H+ NADPH ATP ADP +NADP + NADPH NADP ATP ADP + P i Calvin Cycle Photon H2OH2O 2e – Fd PC PQ 1. Photosystem II absorbs photons, exciting electrons that are passed to plastoquinone (PQ). Electrons lost from photosystem II are replaced by the oxidation of water, producing O 2 2. The b 6 -f complex receives electrons from PQ and passes them to plastocyanin (PC). This provides energy for the b 6 -f complex to pump protons into the thylakoid. 3. Photosystem I absorbs photons, exciting electrons that are passed through a carrier to reduce NADP + to NADPH. These electrons are replaced by electron transport from photosystem II. 4. ATP synthase uses the proton gradient to synthesize ATP from ADP and P i enzyme acts as a channel for protons to diffuse back into the stroma using this energy to drive the synthesis of ATP. NADP reductase ATP synthase 1/2O21/2O2 2H + Water-splitting enzyme Thylakoid space Antenna complex Thylakoid membrane Light-Dependent Reactions H+H+ H+H+ 2e – 10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4 PiPi 12 NADP ADP NADPH NADP + ATP ADP+PiPi Glucose and other sugars Light-Dependent Reactions Calvin Cycle 6 molecules of 12 molecules of 1,3-bisphosphoglycerate (3C) 12 molecules of Glyceraldehyde 3-phosphate (3C) (G3P) 10 molecules of Glyceraldehyde 3-phosphate (3C) (G3P) Stroma of chloroplast 6 molecules of Carbon dioxide (CO 2 ) 12 NADPH 12 ATP 6 ADP 6 ATP Rubisco Calvin Cycle PiPi Ribulose 1,5-bisphosphate (5C) (RuBP) 3-phosphoglycerate (3C) (PGA) Glyceraldehyde 3-phosphate (3C) 2 molecules of 11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O2O2 Heat ATP NADPH NADH ATP Sunlight Pyruvate CO 2 Glucose ADP + P i NAD + NADP i H2OH2O Photo- system II Photo- system I Electron Transport System ADP + P i ATP Calvin Cycle Krebs Cycle 12

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Heat Stomata O2O2 O2O2 CO 2 Under hot, arid conditions, leaves lose water by evaporation through openings in the leaves called stomata. The stomata close to conserve water but as a result, O 2 builds up inside the leaves, and CO 2 cannot enter the leaves. Leaf epidermis H2OH2OH2OH2O 14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CO 2 RuBP 3PG (C 3 ) a. C 4 pathway Bundle-sheath cellMesophyll cell Stoma Vein G3P b. C 4 pathway Stoma Vein Mesophyll cell G3 CO 2 C4C4 Bundle- sheath cell Mesophyll cell Bundle- sheath cell Calvin Cycle Mesophyll cell Calvin Cycle a: © John Shaw/Photo Researchers, Inc. b: © Joseph Nettis/National Audubon Society Collection/Photo Researchers, Inc. 15

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oxaloacetate PyruvateMalate Glucose MalatePyruvate + P i Mesophyll cell Phosphoenolpyruvate (PEP) Bundle-sheath cell Calvin Cycle AMP + PP i ATP CO 2 16

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. night day CO 2 C4C4 G3P Calvin Cycle © ClydeH. Smith/Peter Arnold Inc. 17