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10  photosynthesis text 10 photosynthesis text Presentation Transcript

  • Chapter 10PhotosynthesisPowerPoint Lectures forBiology, Seventh Edition Neil Campbell and Jane ReeceLectures by Chris RomeroCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Overview: The Process That Feeds the Biosphere • Photosynthesis – Is the process that converts solar energy into chemical energyCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Plants and other autotrophs – Are the producers of the biosphereCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Plants are photoautotrophs – They use the energy of sunlight to make organic molecules from water and carbon dioxide Figure 10.1Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Photosynthesis – Occurs in plants, algae, certain other protists, and some prokaryotes These organisms use light energy to drive the synthesis of organic molecules from carbon dioxide and (in most cases) water. They feed not only themselves, but the entire living world. (a) On land, plants are the predominant producers of food. In aquatic environments, photosynthetic organisms include (b) multicellular algae, such as this kelp; (c) some unicellular protists, such as Euglena; (d) the prokaryotes called cyanobacteria; and (e) other photosynthetic prokaryotes, such as these purple sulfur bacteria, which produce sulfur (spherical (a) Plants globules) (c, d, e: LMs). (c) Unicellular protist 10 µm (e) Pruple sulfur 1.5 µm bacteria Figure 10.2 (b) Multicellular algae (d) Cyanobacteria 40 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Heterotrophs – Obtain their organic material from other organisms – Are the consumers of the biosphereCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Concept 10.1: Photosynthesis converts light energy to the chemical energy of foodCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Chloroplasts: The Sites of Photosynthesis in Plants • The leaves of plants – Are the major sites of photosynthesis Leaf cross section Vein Mesophyll CO2 O2 Stomata Figure 10.3Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Chloroplasts – Are the organelles in which photosynthesis occurs – Contain thylakoids and grana Mesophyll Chloroplast 5 µm Outer membrane Thylakoid Thylakoid Intermembrane Stroma Granum space space Inner membrane 1 µmCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Tracking Atoms Through Photosynthesis: Scientific Inquiry • Photosynthesis is summarized as 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2 OCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • The Splitting of Water • Chloroplasts split water into – Hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2 Figure 10.4Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Photosynthesis as a Redox Process • Photosynthesis is a redox process – Water is oxidized, carbon dioxide is reducedCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • The Two Stages of Photosynthesis: A Preview • Photosynthesis consists of two processes – The light reactions – The Calvin cycleCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The light reactions – Occur in the grana – Split water, release oxygen, produce ATP, and form NADPHCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The Calvin cycle – Occurs in the stroma – Forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing powerCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • An overview of photosynthesis H2O CO2 Light NADP + ADP + P LIGHT CALVIN REACTIONS CYCLE ATP NADPH Chloroplast [CH2O] O2 Figure 10.5 (sugar)Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPHCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • The Nature of Sunlight • Light – Is a form of electromagnetic energy, which travels in wavesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Wavelength – Is the distance between the crests of waves – Determines the type of electromagnetic energyCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The electromagnetic spectrum – Is the entire range of electromagnetic energy, or radiation 1m 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 106 nm 103 m Gamma Micro- Radio rays X-rays UV Infrared waves waves Visible light 380 450 500 550 600 650 700 750 nm Shorter wavelength Longer wavelength Higher energy Lower energyFigure 10.6 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The visible light spectrum – Includes the colors of light we can see – Includes the wavelengths that drive photosynthesisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Photosynthetic Pigments: The Light Receptors • Pigments – Are substances that absorb visible lightCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • – Reflect light, which include the colors we see Light Reflected Light Chloroplast Absorbed Granum light Transmitted light Figure 10.7Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The spectrophotometer – Is a machine that sends light through pigments and measures the fraction of light transmitted at each wavelengthCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • An absorption spectrum – Is a graph plotting light absorption versus wavelength White Refracting Chlorophyll Photoelectric light prism solution tube Galvanometer 2 3 1 0 100 4 Slit moves to Green The high transmittance pass light light (low absorption) of selected reading indicates that wavelength chlorophyll absorbs very little green light. 0 100 The low transmittance Blue (high absorption) reading light Figure 10.8 chlorophyll absorbs most blue light.Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The absorption spectra of chloroplast pigments – Provide clues to the relative effectiveness of different wavelengths for driving photosynthesisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The absorption spectra of three types of pigments in chloroplasts EXPERIMENT Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. RESULTS Chlorophyll a Chlorophyll b Absorption of light by chloroplast pigments Carotenoids Wavelength of light (nm) (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Figure 10.9Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The action spectrum of a pigment – Profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis (measured by O2 release) Rate of photosynthesis (b) Action spectrum. This graph plots the rate of photosynthesis versus wavelength. The resulting action spectrum resembles the absorption spectrum for chlorophyll a but does not match exactly (see part a). This is partly due to the absorption of light by accessory pigments such as chlorophyll b and carotenoids.Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The action spectrum for photosynthesis – Was first demonstrated by Theodor W. Engelmann Aerobic bacteria Filament of alga 400 500 600 700 (c) Engelmann‘s experiment. In 1883, Theodor W. Engelmann illuminated a filamentous alga with light that had been passed through a prism, exposing different segments of the alga to different wavelengths. He used aerobic bacteria, which concentrate near an oxygen source, to determine which segments of the alga were releasing the most O2 and thus photosynthesizing most. Bacteria congregated in greatest numbers around the parts of the alga illuminated with violet-blue or red light. Notice the close match of the bacterial distribution to the action spectrum in part b. CONCLUSION Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis.Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Chlorophyll a – Is the main photosynthetic pigment CH3 in chlorophyll a • Chlorophyll b CH2 CHO in chlorophyll b CH H CH3 – Is an accessory pigment H3 C C C C C C C C CH2 CH3 Porphyrin ring: Light-absorbing C N N C “head” of molecule H C Mg C H note magnesium H3 C C N N C atom at center C C C C CH3 H C C C CH2 H H C C CH2 O O C O O O CH3 CH2 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Figure 10.10Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Other accessory pigments – Absorb different wavelengths of light and pass the energy to chlorophyll aCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Excitation of Chlorophyll by Light • When a pigment absorbs light – It goes from a ground state to an excited state, which is unstable Excited e– state Energy of election Heat Photon (fluorescence) Ground Photon Chlorophyll state molecule Figure 10.11 ACopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • If an isolated solution of chlorophyll is illuminated – It will fluoresce, giving off light and heat Figure 10.11 BCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • A Photosystem: A Reaction Center Associated with Light-Harvesting ComplexesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • A photosystem – Is composed of a reaction center surrounded by a number of light-harvesting complexes Thylakoid Photon Photosystem STROMA Light-harvesting Reaction Primary election complexes center acceptor Thylakoid membrane e– Transfer Special Pigment of energy chlorophyll a molecules molecules THYLAKOID SPACE Figure 10.12 (INTERIOR OF THYLAKOID)Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The light-harvesting complexes – Consist of pigment molecules bound to particular proteins – Funnel the energy of photons of light to the reaction centerCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • When a reaction-center chlorophyll molecule absorbs energy – One of its electrons gets bumped up to a primary electron acceptorCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The thylakoid membrane – Is populated by two types of photosystems, I and IICopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Noncyclic Electron Flow • Noncyclic electron flow – Is the primary pathway of energy transformation in the light reactionsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Produces NADPH, ATP, and oxygen H2 O CO2 Light NADP+ ADP LIGHT CALVIN REACTIONS CYCLE ATP NADPH El Tra ectro O2 [CH2O] (sugar) ns n ch por ain t Primary acceptor 7 Primary Elec 4 acceptor tr on t Fd ra ns Pq por t 2 c ha i e 8 n e– H2O e NADP+ Cytochrome 2 H+ NADP + + 2 H+ complex + reductase 3 O2 NADPH PC e– + H+ e– 5 P700 Light 1 P680 Light 6 ATP Photosystem-I Photosystem II Figure 10.13 (PS II) (PS I)Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • A mechanical analogy for the light reactions e– ATP e– e– NADPH e– e– e – Mill on makes Phot ATP e– n P h ot o Photosystem II Photosystem IFigure 10.14Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Cyclic Electron Flow • Under certain conditions – Photoexcited electrons take an alternative pathCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • In cyclic electron flow – Only photosystem I is used – Only ATP is produced Primary Primary acceptor Fd acceptor Fd Pq NADP+ NADP+ reductase Cytochrome NADPH complex Pc ATP Photosystem I Photosystem II Figure 10.15Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • A Comparison of Chemiosmosis in Chloroplasts and Mitochondria • Chloroplasts and mitochondria – Generate ATP by the same basic mechanism: chemiosmosis – But use different sources of energy to accomplish thisCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The spatial organization of chemiosmosis – Differs in chloroplasts and mitochondria Key Higher [H+] Lower [H+] Mitochondrion Chloroplast MITOCHONDRION CHLOROPLAST STRUCTURE STRUCTURE H+ Diffusion Intermembrance Thylakoid space Electron space Membrance transport chain ATP Synthase Stroma Matrix ADP+ P ATP H+ Figure 10.16Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • In both organelles – Redox reactions of electron transport chains generate a H+ gradient across a membrane • ATP synthase – Uses this proton-motive force to make ATPCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The light reactions and chemiosmosis: the organization of the thylakoid membrane H2O CO2 LIGHT NADP+ ADP CALVIN LIGHT CYCLE REACTOR ATP NADPH STROMA O2 [CH2O] (sugar) (Low H+ concentration) Cytochrome Photosystem II complex Photosystem I Light NADP+ 2 H+ reductase 3 Fd NADP+ + 2H+ NADPH + H+ Pq Pc 2 H2 O 1 ⁄2 O2 THYLAKOID SPACE 1 2 H+ +2 H+ (High H+ concentration) To Calvin cycle ATP Thylakoid synthase STROMA membrane ADP (Low H+ concentration) ATP P H + Figure 10.17Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar • The Calvin cycle – Is similar to the citric acid cycle – Occurs in the stromaCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The Calvin cycle has three phases – Carbon fixation – Reduction – Regeneration of the CO2 acceptorCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The Calvin cycle H2O CO2 Light Input NADP+ 3 (Entering one ADP CALVIN CO2 at a time) LIGHT REACTION CYCLE ATP NADPH Phase 1: Carbon fixation Rubisco O2 [CH2O] (sugar) 3 P P Short-lived intermediate 6 P 3 P P Ribulose bisphosphate 3-Phosphoglycerate (RuBP) 6 ATP 6 ADP 3 ADP CALVIN CYCLE 6 P P 3 ATP 1,3-Bisphoglycerate 6 NADPH Phase 3: Regeneration of 6 NADPH+ the CO2 acceptor 6 P (RuBP) 5 P (G3P) 6 P Glyceraldehyde-3-phosphate Phase 2: (G3P) Reduction 1 P G3P Glucose and Figure 10.18 (a sugar) other organic Output compoundsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Concept 10.4: Alternative mechanisms of carbon fixation have evolved in hot, arid climatesCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • On hot, dry days, plants close their stomata – Conserving water but limiting access to CO 2 – Causing oxygen to build upCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • Photorespiration: An Evolutionary Relic? • In photorespiration – O2 substitutes for CO2 in the active site of the enzyme rubisco – The photosynthetic rate is reducedCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • C4 Plants • C4 plants minimize the cost of photorespiration – By incorporating CO2 into four carbon compounds in mesophyll cellsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • These four carbon compounds – Are exported to bundle sheath cells, where they release CO2 used in the Calvin cycleCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • C4 leaf anatomy and the C4 pathway Mesophyll cell Mesophyll Photosynthetic cell CO CO2 2 PEP carboxylase cells of C4 plant Bundle- leaf sheath cell Oxaloacetate (4 C) PEP (3 C) Vein ADP (vascular tissue) Malate (4 C) ATP C4 leaf anatomy Bundle- Pyruate (3 C) Sheath cell CO2 Stoma CALVIN CYCLE Sugar Vascular tissue Figure 10.19Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • CAM Plants • CAM plants – Open their stomata at night, incorporating CO 2 into organic acidsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • During the day, the stomata close – And the CO2 is released from the organic acids for use in the Calvin cycleCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • The CAM pathway is similar to the C4 pathway Sugarcane Pineapple C4 CAM CO2 CO2 Mesophyll Cell Night Organic acid 1 CO2 incorporated Organic acid Bundle- into four-carbon sheath organic acids (carbon fixation) Day cell (a) Spatial separation (b) Temporal separation of steps. In C4 CALVIN 2 Organic acids CALVIN of steps. In CAM plants, carbon fixation CYCLE release CO2 to CYCLE plants, carbon fixation and the Calvin cycle Calvin cycle and the Calvin cycle occur in different occur in the same cells Sugar SugarFigure 10.20 types of cells. at different times. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • The Importance of Photosynthesis: A Review • A review of photosynthesis Light reaction Calvin cycle H2O CO2 Light NADP+ ADP +P1 RuBP 3-Phosphoglycerate Photosystem II Electron transport chain Photosystem I ATP G3P NADPH Starch (storage) Amino acids Fatty acids Chloroplast O2 Sucrose (export) Calvin cycle reactions: Light reactions: • Take place in the stroma • Are carried out by molecules in the • Use ATP and NADPH to convert thylakoid membranes CO2 to the sugar G3P • Convert light energy to the chemical energy of ATP and NADPH • Return ADP, inorganic phosphate, • Split H2O and release O2 to the and Figure 10.21 NADP+ to the light reactions atmosphereCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
  • • Organic compounds produced by photosynthesis – Provide the energy and building material for ecosystemsCopyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings