植物生理學

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(1)CAMPBELL. BIOLOGY. TENTH EDITION. Reece • Urry • Cain • Wasserman • Minorsky • Jackson. 11 Photosynthetic Processes. Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick © 2014 Pearson Education, Inc..

(2) The Process That Feeds the Biosphere  Photosynthesis is the process that converts solar energy into chemical energy  Directly or indirectly, photosynthesis nourishes almost the entire living world. © 2014 Pearson Education, Inc..

(3)  Autotrophs sustain themselves without eating anything derived from other organisms  Autotrophs are the producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules  Almost all plants are photoautotrophs, using the energy of sunlight to make organic molecules. © 2014 Pearson Education, Inc..

(4) Figure 11.1. © 2014 Pearson Education, Inc..

(5) Figure 11.1a. Other organisms also benefit from photosynthesis.. © 2014 Pearson Education, Inc..

(6)  Photosynthesis occurs in plants, algae, certain other unicellular eukaryotes, and some prokaryotes  These organisms feed not only themselves but also most of the living world. © 2014 Pearson Education, Inc..

(7) Figure 11.2. (d) Cyanobacteria. (b) Multicellular alga. 1 μm. (a) Plants. 11 μm. (e) Purple sulfur bacteria. (c) Unicellular eukaryotes. © 2014 Pearson Education, Inc.. 40 μm.

(8) Figure 11.2a. (a) Plants. © 2014 Pearson Education, Inc..

(9) Figure 11.2b. (b) Multicellular alga. © 2014 Pearson Education, Inc..

(10) 11 μm. Figure 11.2c. © 2014 Pearson Education, Inc.. (c) Unicellular eukaryotes.

(11) Figure 11.2d. (d) Cyanobacteria. © 2014 Pearson Education, Inc.. 40 μm.

(12) 1 μm. Figure 11.2e. © 2014 Pearson Education, Inc.. (e) Purple sulfur bacteria.

(13)  Heterotrophs obtain their organic material from other organisms  Heterotrophs are the consumers of the biosphere.  Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2. © 2014 Pearson Education, Inc..

(14)  Earth’s supply of fossil fuels was formed from the remains of organisms that died hundreds of millions of years ago  In a sense, fossil fuels represent stores of solar energy from the distant past. © 2014 Pearson Education, Inc..

(15) Figure 11.3. © 2014 Pearson Education, Inc..

(16) Concept 11.1: Photosynthesis converts light energy to the chemical energy of food  Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria  The structural organization of these organelles allows for the chemical reactions of photosynthesis. © 2014 Pearson Education, Inc..

(17) Chloroplasts: The Sites of Photosynthesis in Plants  Leaves are the major locations of photosynthesis  Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of the leaf.  Each mesophyll cell contains 30–40 chloroplasts  CO2 enters and O2 exits the leaf through microscopic pores called stomata. © 2014 Pearson Education, Inc..

(18)  A chloroplast has an envelope of two membranes surrounding a dense fluid called the stroma  Thylakoids are connected sacs in the chloroplast which compose a third membrane system  Thylakoids may be stacked in columns called grana  Chlorophyll, the pigment which gives leaves their green colour, resides in the thylakoid membranes. © 2014 Pearson Education, Inc..

(19) Figure 11.4. Leaf cross section Chloroplasts Vein. Mesophyll. Stomata CO2. O2. Chloroplast Mesophyll cell. Thylakoid Thylakoid Stroma Granum space. 1 μm © 2014 Pearson Education, Inc.. Outer membrane Intermembrane space Inner membrane. 20 μm.

(20) Figure 11.4a. Leaf cross section Chloroplasts Vein. Mesophyll. Stomata CO2. O2. Chloroplast Mesophyll cell. 20 μm © 2014 Pearson Education, Inc..

(21) Figure 11.4b. Chloroplast. Thylakoid Thylakoid Stroma Granum space. 1 μm. © 2014 Pearson Education, Inc.. Outer membrane Intermembrane space Inner membrane.

(22) Figure 11.4c. Stroma. Granum. 1 μm. © 2014 Pearson Education, Inc..

(23) Figure 11.4d. Mesophyll cell. 20 μm. © 2014 Pearson Education, Inc..

(24) Tracking Atoms Through Photosynthesis: Scientific Inquiry  Photosynthesis is a complex series of reactions that can be summarized as the following equation: 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O.  The overall chemical change during photosynthesis is the reverse of the one that occurs during cellular respiration. © 2014 Pearson Education, Inc..

(25) The Splitting of Water  Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product. © 2014 Pearson Education, Inc..

(26) Figure 11.5. Reactants:. Products:. © 2014 Pearson Education, Inc.. 6 CO2. C6H12O6. 12 H2O. 6 H2O. 6 O2.

(27) Photosynthesis as a Redox Process  Photosynthesis reverses the direction of electron flow compared to respiration  Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced  Photosynthesis is an endergonic process; the energy boost is provided by light. © 2014 Pearson Education, Inc..

(28) Figure 11.UN01. becomes reduced. becomes oxidized. © 2014 Pearson Education, Inc..

(29) The Two Stages of Photosynthesis: A Preview  Photosynthesis consists of the light reactions (the photo part) and Calvin cycle (the synthesis part)  The light reactions (in the thylakoids)  Split H2O  Release O2  Reduce the electron acceptor NADP+ to NADPH  Generate ATP from ADP by photophosphorylation © 2014 Pearson Education, Inc..

(30)  The Calvin cycle (in the stroma) forms sugar from CO2, using ATP and NADPH  The Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules. © 2014 Pearson Education, Inc..

(31) Figure 11.6-1. Light. H2O. NADP+. LIGHT REACTIONS Thylakoid. Chloroplast. © 2014 Pearson Education, Inc.. ADP + Pi. Stroma.

(32) Figure 11.6-2. Light. H2O. NADP+. LIGHT REACTIONS. ADP + Pi ATP. Thylakoid. NADPH. Chloroplast O2. © 2014 Pearson Education, Inc.. Stroma.

(33) Figure 11.6-3. Light. H2O. CO2. NADP+. LIGHT REACTIONS. ADP + Pi ATP. Thylakoid. NADPH. Chloroplast O2. © 2014 Pearson Education, Inc.. CALVIN CYCLE Stroma.

(34) Figure 11.6-4. Light. H2O. CO2. NADP+. LIGHT REACTIONS. ADP + Pi. CALVIN CYCLE. ATP. Thylakoid. Stroma. NADPH. Chloroplast O2. © 2014 Pearson Education, Inc.. [CH2O] (sugar).

(35) BioFlix: The Carbon Cycle. © 2014 Pearson Education, Inc..

(36) BioFlix: Photosynthesis. © 2014 Pearson Education, Inc..

(37) Concept 11.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH  Chloroplasts are solar-powered chemical factories  Their thylakoids transform light energy into the chemical energy of ATP and NADPH. © 2014 Pearson Education, Inc..

(38) The Nature of Sunlight  Light is a form of electromagnetic energy, also called electromagnetic radiation  Like other electromagnetic energy, light travels in rhythmic waves  Wavelength is the distance between crests of waves  Wavelength determines the type of electromagnetic energy. © 2014 Pearson Education, Inc..

(39)  The electromagnetic spectrum is the entire range of electromagnetic energy, or radiation  Visible light consists of wavelengths (including those that drive photosynthesis) that produce colors we can see  Light also behaves as though it consists of discrete particles, called photons. © 2014 Pearson Education, Inc..

(40) Figure 11.7. 11− 5 nm 11− 3 nm 1 nm Gamma X-rays rays. 11 3 nm. UV. 11 6 nm. Infrared. 1m (11 9 nm). Microwaves. 11 3 m. Radio waves. Visible light. 380. 450. 500. Shorter wavelength Higher energy © 2014 Pearson Education, Inc.. 550. 600. 650. 700. 750 nm. Longer wavelength Lower energy.

(41) Photosynthetic Pigments: The Light Receptors  Pigments are substances that absorb visible light  Different pigments absorb different wavelengths  Wavelengths that are not absorbed are reflected or transmitted  Leaves appear green because chlorophyll reflects and transmits green light. © 2014 Pearson Education, Inc..

(42) Figure 11.8. Light Reflected light Chloroplast. Absorbed light. Granum. Transmitted light © 2014 Pearson Education, Inc..

(43) Animation: Light and Pigments. © 2014 Pearson Education, Inc..

(44)  A spectrophotometer measures a pigment’s ability to absorb various wavelengths  This machine sends light through pigments and measures the fraction of light transmitted at each wavelength. © 2014 Pearson Education, Inc..

(45) Figure 11.9. Refracting prism. White light. Chlorophyll solution 2. 1. Slit moves to pass light of selected wavelength.. © 2014 Pearson Education, Inc.. Photoelectric tube Galvanometer. 3 4. Green light. The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light.. Blue light. The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light..

(46)  An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelength  The absorption spectrum of chlorophyll a suggests that violet-blue and red light work best for photosynthesis  An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a process. © 2014 Pearson Education, Inc..

(47) Absorption of light by chloroplast pigments. Figure 11.10. Chlorophyll a. Chlorophyll b Carotenoids. 500 600 700 Wavelength of light (nm) (a) Absorption spectra Rate of photosynthesis (measured by O2 release). 400. 400 500 (b) Action spectrum. 600. 700. Aerobic bacteria Filament of alga. 400 500 (c) Engelmann’s experiment © 2014 Pearson Education, Inc.. 600. 700.

(48) Absorption of light by chloroplast pigments. Figure 11.10a. Chlorophyll a. Chlorophyll b Carotenoids. 400. 500 600 700 Wavelength of light (nm) (a) Absorption spectra. © 2014 Pearson Education, Inc..

(49) Rate of photosynthesis (measured by O2 release). Figure 11.10b. 500 400 (b) Action spectrum. © 2014 Pearson Education, Inc.. 600. 700.

(50) Figure 11.10c. Aerobic bacteria Filament of alga. 400 500 600 (c) Engelmann’s experiment. © 2014 Pearson Education, Inc.. 700.

(51)  The action spectrum of photosynthesis was first demonstrated in 1883 by Theodor W. Engelmann  In his experiment, he exposed different segments of a filamentous alga to different wavelengths  Areas receiving wavelengths favorable to photosynthesis produced excess O2  He used the growth of aerobic bacteria clustered along the alga as a measure of O2 production. © 2014 Pearson Education, Inc..

(52)  Chlorophyll a is the main photosynthetic pigment  Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesis.  The difference in the absorption spectrum between chlorophyll a and b is due to a slight structural difference between the pigment molecules  Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll © 2014 Pearson Education, Inc..

(53) Figure 11.11. CH3. CH3 in chlorophyll a CHO in chlorophyll b Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center. Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown © 2014 Pearson Education, Inc..

(54) Video: Space-Filling Model of Chlorophyll a. © 2014 Pearson Education, Inc..

(55)  Accessory pigments called carotenoids function in photoprotection; they absorb excessive light that would damage chlorophyll. © 2014 Pearson Education, Inc..

(56) Sun Radiation Chlorophyll is the main photosynthetic pigment Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis..

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(59) porphyrin ring. phytol tail Chlorophylls consist of a light-absorbing with a magnesium atom at the center and a long phytol tail that anchors the molecule in a membrane (Figure 1). They absorb light in the blue and red parts of the spectrum, but the green wavelengths are transmitted or reflected..

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(61) absorption spectrum.

(62) Phycobiliprotein in cyanobacteria In oceanic waters, cyanobacteria comprise only two main genera: Synechococcus and Prochlorococcus. These antennae (called "phycobilisomes" in Synechococcus) are composed of pigmentproteins complexes arranged in such a way to capture light with a high efficiency. Pigments that are bound to antenna systems may have very different colours (such as green, blue, pink or orange) and this will determine the wavelengths of the solar spectrum that cells can efficiently harvest in the oceanic waters..

(63) complementary chromatic adaptation (CCA) The Journal of Biological Chemistry, 276, 11449-11452 (2001).

(64) Phycobiliproteins, bilin variation, and group III CA regulation.. Kehoe D M PNAS 2010;107:9029-9030. © 2010 by National Academy of Sciences.

(65) complementary chromatic illuminated Structure of a hemidiscoidal adaptation by white phycobilisome of Tolypothrix tenuis under different light conditions. (a) When illuminated by white light, the phycobilisome contains phycoerythrin, phycocyanin, and allophycocyanin. Energy absorbed by phycoerythrin is transferred to phycocyanin and allophycocyanin. The allophycocyanin core proteins are attached, via a linker protein, to the photosynthetic membrane, which is not shown. (b) When illuminated by red light, the phycobilisome undergoes complementary chromatic adaptation, in which phycoerythrin is no longer produced but additional phycocyanin is produced. (After R. MacColl and D. Guard-Friar, Phycobiliproteins, CRC Press, Boca Raton, FL, 1987). light. illuminated by red light.

(66) Excitation of Chlorophyll by Light  When a pigment absorbs light, it goes from a ground state to an excited state, which is unstable  When excited electrons fall back to the ground state, photons are given off, an afterglow called fluorescence  If illuminated, an isolated solution of chlorophyll will fluoresce, giving off light and heat. © 2014 Pearson Education, Inc..

(67) Figure 11.12. Energy of electron. e−. Excited state Heat. Photon. Chlorophyll molecule. Photon (fluorescence) Ground state. (a) Excitation of isolated chlorophyll molecule. © 2014 Pearson Education, Inc.. (b) Fluorescence.

(68) Figure 11.12a. (b) Fluorescence. © 2014 Pearson Education, Inc..

(69) Electron transport chain (ETC).

(70) A Photosystem: A Reaction-Center Complex Associated with Light-Harvesting Complexes  A photosystem consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexes  The light-harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction center. © 2014 Pearson Education, Inc..

(71) Figure 11.13. Photosystem STROMA ReactionPrimary center complex electron acceptor. e−. Transfer of energy. Special pair of chlorophyll a molecules Pigment THYLAKOID SPACE molecules (INTERIOR OF THYLAKOID). (a) How a photosystem harvests light. © 2014 Pearson Education, Inc.. Thylakoid membrane. Lightharvesting complexes. Thylakoid membrane. Photon. Chlorophyll. Protein subunits (b) Structure of a photosystem. STROMA. THYLAKOID SPACE.

(72) Figure 11.13a. Photosystem. Thylakoid membrane. Photon. Lightharvesting complexes. STROMA ReactionPrimary center complex electron acceptor. e−. Transfer of energy. Special pair of chlorophyll a molecules Pigment THYLAKOID SPACE molecules (INTERIOR OF THYLAKOID). (a) How a photosystem harvests light © 2014 Pearson Education, Inc..

(73) Thylakoid membrane. Figure 11.13b. Chlorophyll. Protein subunits (b) Structure of a photosystem. © 2014 Pearson Education, Inc.. STROMA. THYLAKOID SPACE.

(74) Photosystem II (PSII) Photosystem II contains chlorophylls a and b and absorbs light at 680nm. This is a large protein complex that is located in the thylakoid membrane..

(75) LHC-II  MOST ABUNDANT MEMBRANE PROTEIN IN CHLOROPLASTS OF GREEN PLANTS  A TRANSMEMBRANE PROTEIN  BINDS  ~ 7 CHLOROPHYLL a MOLECULES  ~ 5 CHLOROPHYLL b MOLECULES  TWO CAROTENOIDS.  COMPRISES ABOUT 50% OF ALL CHLOROPHYLL IN BIOSPHERE.

(76) LH2 FROM Rs. acidophhilus.

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(79)  A primary electron acceptor in the reaction center accepts excited electrons and is reduced as a result  Solar-powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions. © 2014 Pearson Education, Inc..

(80)  There are two types of photosystems in the thylakoid membrane  Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm  The reaction-center chlorophyll a of PS II is called P680. © 2014 Pearson Education, Inc..

(81)  Photosystem I (PS I) is best at absorbing a wavelength of 700 nm  The reaction-center chlorophyll a of PS I is called P700. © 2014 Pearson Education, Inc..

(82) Linear Electron Flow  During the light reactions, there are two possible routes for electron flow: cyclic and linear  Linear electron flow, the primary pathway, involves both photosystems and produces ATP and NADPH using light energy. © 2014 Pearson Education, Inc..

(83)  There are 8 steps in linear electron flow: 1. A photon hits a pigment and its energy is passed among pigment molecules until it excites P680. 2. An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+). © 2014 Pearson Education, Inc..

(84) Figure 11.UN02. H2O. CO2. Light. NADP+ ADP CALVIN CYCLE. LIGHT REACTIONS ATP. NADPH. O2 © 2014 Pearson Education, Inc.. [CH2O] (sugar).

(85) Figure 11.14-1. Primary acceptor. e−. 1. 2. P680. Light. Pigment molecules Photosystem II (PS II). © 2014 Pearson Education, Inc..

(86) Figure 11.14-2. Primary acceptor. 2 H+ + ½ O2 1. H2O. e−. 2. 3 e− e−. P680. Light. Pigment molecules Photosystem II (PS II). © 2014 Pearson Education, Inc..

(87) Figure 11.14-3. 4 Primary acceptor. 2 ½. H+. +. O2. 1. H2O. e−. 2. Pq Cytochrome complex. 3 e− e−. Electron transport chain. Pc. P680. 5. Light ATP. Pigment molecules Photosystem II (PS II). © 2014 Pearson Education, Inc..

(88) Figure 11.14-4. 4 Primary acceptor. 2 H+ + ½ O2 1. H2O. e−. 2. Primary acceptor. e−. Pq Cytochrome complex. 3 e− e−. Electron transport chain. Pc. P680. P700. 5. Light. Light. 6. ATP. Pigment molecules Photosystem II (PS II). © 2014 Pearson Education, Inc.. Photosystem I (PS I).

(89) Figure 11.14-5. 4 Primary acceptor. 2 ½. H+. +. O2. 1. H2O. e−. 2. Electron transport chain. e−. 8. NADP+ reductase Pc. P680. e− − e. Fd. e−. Pq. e−. Electron transport chain. Primary acceptor. Cytochrome complex. 3. 7. P700. 5. Light. Light. 6. ATP. Pigment molecules Photosystem II (PS II). © 2014 Pearson Education, Inc.. Photosystem I (PS I). NADP+ + H+ NADPH.

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(91) 3. H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680  P680+ is the strongest known biological oxidizing agent  O2 is released as a by-product of this reaction. © 2014 Pearson Education, Inc..

(92) 4. Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I 5. Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane  Diffusion of H+ (protons) across the membrane drives ATP synthesis. © 2014 Pearson Education, Inc..

(93) 6. In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor  P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the electron transport chain. © 2014 Pearson Education, Inc..

(94) 7. Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd) 8. The electrons are then transferred to NADP+ and reduce it to NADPH  The electrons of NADPH are available for the reactions of the Calvin cycle.  This process also removes an H+ from the stroma. © 2014 Pearson Education, Inc..

(95)  The energy changes of electrons during linear flow through the light reactions can be shown in a mechanical analogy. © 2014 Pearson Education, Inc..

(96) Figure 11.15. e−. e−. e−. e−. Mill makes ATP e−. NADPH e−. e−. ATP. Photosystem II © 2014 Pearson Education, Inc.. Photosystem I.

(97) Cyclic Electron Flow  In cyclic electron flow, electrons cycle back from Fd to the PS I reaction center  Cyclic electron flow uses only photosystem I and produces ATP, but not NADPH  No oxygen is released. © 2014 Pearson Education, Inc..

(98) Figure 11.16. Primary acceptor. Primary acceptor. Fd. Fd Pq. NADP+ reductase. Cytochrome complex. NADPH. Pc. Photosystem I Photosystem II. © 2014 Pearson Education, Inc.. ATP. NADP+ + H+.

(99)  Some organisms such as purple sulfur bacteria have PS I but not PS II  Cyclic electron flow is thought to have evolved before linear electron flow  Cyclic electron flow may protect cells from light-induced damage. © 2014 Pearson Education, Inc..

(100) Cyclic Electron Flow. • Electron in Photosystem I is excited and transferred to ferredoxin that shuttles the electron to the cytochrome complex. • The electron then travels down the electron chain and re-enters photosystem I.

(101) Green tide.

(102) A Comparison of Chemiosmosis in Chloroplasts and Mitochondria  Chloroplasts and mitochondria generate ATP by chemiosmosis, but use different sources of energy  Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP  Spatial organization of chemiosmosis differs between chloroplasts and mitochondria but also shows similarities. © 2014 Pearson Education, Inc..

(103)  In mitochondria, protons are pumped to the intermembrane space and drive ATP synthesis as they diffuse back into the mitochondrial matrix  In chloroplasts, protons are pumped into the thylakoid space and drive ATP synthesis as they diffuse back into the stroma. © 2014 Pearson Education, Inc..

(104) Figure 11.17. CHLOROPLAST STRUCTURE. MITOCHONDRION STRUCTURE Intermembrane space Inner membrane. H+. Diffusion. Electron transport chain. Thylakoid space Thylakoid membrane. ATP synthase Stroma. Matrix ADP + P i. Key. Higher [H+] Lower [H+] © 2014 Pearson Education, Inc.. H+. ATP.

(105)  ATP and NADPH are produced on the side facing the stroma, where the Calvin cycle takes place  In summary, light reactions generate ATP and increase the potential energy of electrons by moving them from H2O to NADPH. © 2014 Pearson Education, Inc..

(106) Figure 11.18. Cytochrome Photosystem II complex Light + 4H Light. NADP+ reductase 3. Photosystem I. Fd Pq. H2O. e. e. NADPH 2. 1 ½ O2 THYLAKOID SPACE +2 H+ + (high H concentration). NADP+ + H+. Pc. 4 H+ To Calvin Cycle. Thylakoid membrane STROMA (low H+ concentration). © 2014 Pearson Education, Inc.. ATP synthase ADP + Pi. H+. ATP.

(107) Figure 11.18a. Cytochrome Photosystem II complex Light 4 H+ Light. Photosystem I Fd. Pq H2O. e. e. 1 ½. THYLAKOID SPACE (high H+ concentration). O2. +2 H+. Thylakoid membrane STROMA (low H+ concentration) © 2014 Pearson Education, Inc.. Pc. 2 4 H+. ATP synthase ADP + Pi. H+. ATP.

(108) Figure 11.18b. Cytochrome complex Light. NADP+ reductase 3. Photosystem I. Fd Pq. NADP+ + H+. NADPH Pc. 2 4 H+. THYLAKOID SPACE (high H+ concentration) To Calvin Cycle. ATP synthase ADP + Pi © 2014 Pearson Education, Inc.. STROMA (low H+ concentration) H+. ATP.

(109) Concept 11.3: The Calvin cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar  The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle  The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH. © 2014 Pearson Education, Inc..

(110)  Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P)  For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2  The Calvin cycle has three phases 1. Carbon fixation (catalyzed by rubisco) 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP). © 2014 Pearson Education, Inc..

(111) Figure 11.UN03. H2O. CO2. Light. NADP+ ADP CALVIN CYCLE. LIGHT REACTIONS ATP NADPH. O2 © 2014 Pearson Education, Inc.. [CH2O] (sugar).

(112) Figure 11.19-1. Input 3 CO2, entering one per cycle Phase 1: Carbon fixation. Rubisco 3 P. 3 P. 6. P. P. 3-Phosphoglycerate. RuBP Calvin Cycle. © 2014 Pearson Education, Inc.. P.

(113) Figure 11.19-2. Input 3 CO2, entering one per cycle Phase 1: Carbon fixation. Rubisco 3 P. 3 P. P. 6. P. P. 3-Phosphoglycerate. RuBP. 6. ATP. 6 ADP. Calvin Cycle. 6 P. P. 1,3-Bisphosphoglycerate 6 NADPH 6 NADP+ 6 Pi. 6. P. G3P. 1. P. G3P Output © 2014 Pearson Education, Inc.. Phase 2: Reduction. Glucose and other organic compounds.

(114) Figure 11.19-3. Input 3 CO2, entering one per cycle Phase 1: Carbon fixation. Rubisco 3 P. 3 P. P. 6. P. P. 3-Phosphoglycerate. RuBP. 6. ATP. 6 ADP. Calvin Cycle. 3 ADP 3. ATP. 6 P. P. 1,3-Bisphosphoglycerate 6 NADPH. Phase 3: Regeneration of RuBP. 6 NADP+ 6 Pi P. 5. G3P. 6. P. G3P. 1. P. G3P Output © 2014 Pearson Education, Inc.. Phase 2: Reduction. Glucose and other organic compounds.

(115) Concept 11.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climates  Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesis  On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesis  The closing of stomata reduces access to CO2 and causes O2 to build up  These conditions favor an apparently wasteful process called photorespiration © 2014 Pearson Education, Inc..

(116) Photorespiration: An Evolutionary Relic?  In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate)  In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle, producing a two-carbon compound  Photorespiration consumes O2 and organic fuel and releases CO2 without producing ATP or sugar. © 2014 Pearson Education, Inc..

(117)  Photorespiration may be an evolutionary relic because rubisco first evolved at a time when the atmosphere had far less O2 and more CO2  Photorespiration limits damaging products of light reactions that build up in the absence of the Calvin cycle  In many plants, photorespiration is a problem because on a hot, dry day it can drain as much as 50% of the carbon fixed by the Calvin cycle. © 2014 Pearson Education, Inc..

(118) C4 Plants  C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds  There are two distinct types of cells in the leaves of C4 plants:  Bundle-sheath cells are arranged in tightly packed sheaths around the veins of the leaf  Mesophyll cells are loosely packed between the bundle sheath and the leaf surface. © 2014 Pearson Education, Inc..

(119)  Sugar production in C4 plants occurs in a threestep process: 1. The production of the four carbon precursors is catalyzed by the enzyme PEP carboxylase in the mesophyll cells  PEP carboxylase has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low. © 2014 Pearson Education, Inc..

(120) 2. These four-carbon compounds are exported to bundle-sheath cells 3. Within the bundle-sheath cells, they release CO2 that is then used in the Calvin cycle. © 2014 Pearson Education, Inc..

(121) Figure 11.20. C4 leaf anatomy Photosynthetic cells of C4 plant leaf. Mesophyll cell. The C4 pathway Mesophyll cell PEP carboxylase. Bundlesheath cell. Oxaloacetate (4C). Vein (vascular tissue). PEP (3C) ADP. Malate (4C). ATP. Pyruvate CO (3C) 2. Stoma. Bundlesheath cell. Calvin Cycle Sugar. Vascular tissue © 2014 Pearson Education, Inc.. CO2.

(122) Figure 11.20a. C4 leaf anatomy Photosynthetic cells of C4 plant leaf. Mesophyll cell Bundlesheath cell. Vein (vascular tissue). Stoma. © 2014 Pearson Education, Inc..

(123) Figure 11.20b. The C4 pathway Mesophyll cell PEP carboxylase. Oxaloacetate (4C). PEP (3C) ADP. Malate (4C). ATP. Pyruvate CO (3C) 2. Bundlesheath cell. Calvin Cycle Sugar. Vascular tissue © 2014 Pearson Education, Inc.. CO2.

(124)  Since the Industrial Revolution in the 1800s, CO2 levels have risen greatly  Increasing levels of CO2 may affect C3 and C4 plants differently, perhaps changing the relative abundance of these species.  The effects of such changes are unpredictable and a cause for concern. © 2014 Pearson Education, Inc..

(125) CAM Plants  Some plants, including succulents, use crassulacean acid metabolism (CAM) to fix carbon  CAM plants open their stomata at night, incorporating CO2 into organic acids  Stomata close during the day, and CO2 is released from organic acids and used in the Calvin cycle. © 2014 Pearson Education, Inc..

(126) Figure 11.21. Sugarcane. Pineapple 1. C4 Mesophyll Organic cell acid. CO2 2 Bundlesheath cell. Organic acid. CAM Night. CO2 2. Calvin Cycle. Calvin Cycle. Sugar. Sugar. (a) Spatial separation of steps © 2014 Pearson Education, Inc.. CO2. CO2. 1. Day. (b) Temporal separation of steps.

(127) Figure 11.21a. Sugarcane. © 2014 Pearson Education, Inc..

(128) Figure 11.21b. Pineapple. © 2014 Pearson Education, Inc..

(129) The Importance of Photosynthesis: A Review  The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds  Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells.  Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits  In addition to food production, photosynthesis produces the O2 in our atmosphere © 2014 Pearson Education, Inc..

(130) Figure 11.22a O2. CO2. H2O. Sucrose (export). Mesophyll cell. H2O. Chloroplast. CO2. Light NADP+ LIGHT REACTIONS: Photosystem II Electron transport chain Photosystem I Electron transport chain. H2O © 2014 Pearson Education, Inc.. O2. ADP + Pi. ATP NADPH. 3-Phosphoglycerate RuBP CALVIN CYCLE G3P Starch (storage) Sucrose (export).

(131) Figure 11.22b. LIGHT REACTIONS. • Are carried out by molecules in the thylakoid membranes • Convert light energy to the chemical energy of ATP and NADPH • Split H2O and release O2 to the atmosphere. © 2014 Pearson Education, Inc.. CALVIN CYCLE REACTIONS. • Take place in the stroma • Use ATP and NADPH to convert CO2 to the sugar G3P • Return ADP, inorganic phosphate, and NADP+ to the light reactions.

(132) Figure 11.23. MAKE CONNECTIONS The Working Cell. Nucleus. Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 5–7). Movement Across Cell Membranes (Chapter 7). Energy Transformations in the Cell: Photosynthesis and Cellular Respiration (Chapters 8–11). DNA. 1 mRNA. Nuclear pore 2. Protein 3. Rough endoplasmic Protein reticulum (ER) in vesicle. Vacuole. Ribosome mRNA. 4 Golgi apparatus. Vesicle forming. 7 Photosynthesis in chloroplast. H2 O. Protein. ATP. Organic 8 molecules Cellular respiration O2 in mitochondrion. 6. Plasma membrane 5. CO2. ATP. Transport pump. ATP. 11 ATP. 11. 9 Cell wall. O2 CO2 H2 O. © 2014 Pearson Education, Inc..

(133) Figure 11.23a. Nucleus. DNA. 1 mRNA. Nuclear pore 2 Protein 3. Rough endoplasmic Protein reticulum (ER) in vesicle. Ribosome mRNA Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 5–7). © 2014 Pearson Education, Inc..

(134) Figure 11.23b. 4. Vesicle forming. Golgi apparatus. Protein 6. Plasma membrane 5. Cell wall Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 5–7) © 2014 Pearson Education, Inc..

(135) Figure 11.23c. 7 Photosynthesis in chloroplast. CO2 H2O ATP. Organic 8 molecules Cellular respiration O2 in mitochondrion. ATP. Transport pump. ATP. 11 ATP. Movement Across Cell Membranes (Chapter 7). 11. 9. O2 CO2 H2O. © 2014 Pearson Education, Inc.. Energy Transformations in the Cell: Photosynthesis and Cellular Respiration (Chapters 8–11).

(136) Figure 11.UN04a. © 2014 Pearson Education, Inc..

(137) Figure 11.UN04b. Corn plant surrounded by invasive velvetleaf plants © 2014 Pearson Education, Inc..

(138) Figure 11.UN05. Primary acceptor. Primary acceptor H2O. O2. Fd Pq. NADP+ reductase. Cytochrome complex Pc. Photosystem I. Photosystem II. © 2014 Pearson Education, Inc.. NADP+ + H+ NADPH.

(139) Figure 11.UN06. 3 CO2. Carbon fixation. 3 x 5C. 6 x 3C Calvin Cycle. Regeneration of CO2 acceptor 5 x 3C Reduction. 1 G3P (3C) © 2014 Pearson Education, Inc..

(140) Figure 11.UN07. pH 4. pH 7. pH 4. pH 8. ATP. © 2014 Pearson Education, Inc..

(141) Figure 11.UN08. © 2014 Pearson Education, Inc..

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