Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ch. 10 Photosynthesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Feeds the Biosphere Converts solar E into chemical E

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plants and other autotrophs  Producers of the biosphere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photoautotrophs – Use E of sunlight to make organic molecules from water and CO 2 Figure 10.1

Copyright © 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 globules) (c, d, e: LMs). (a) Plants (b) Multicellular algae (c) Unicellular protist 10  m 40  m (d) Cyanobacteria 1.5  m (e) Pruple sulfur bacteria Figure 10.2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Heterotrophs Obtain organic material f/ other organisms Consumers of the biosphere

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthesis converts light E to the chemical E of food

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts: Site of Photosynthesis (plants) Leaf – Major site of photosynthesis Vein Leaf cross section Figure 10.3 Mesophyll CO 2 O2O2 Stomata

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts – Contain thylakoids and grana Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthesis summary reaction 6 CO H 2 O + Light energy  C 6 H 12 O O H 2 O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts split water into H 2 and O 2, incorporating the e - of H 2 into sugar molecules 6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6H2O6H2O 6O26O2 Figure 10.4

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthesis as a Redox Process Water is oxidized, CO 2 is reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Two Stages of Photosynthesis: A Preview Light reactions Calvin cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light reactions – Occurs on thylakoid membranes – Converts solar E to chemical E

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Calvin cycle – Occurs in the stroma – Forms sugar from carbon dioxide, using ATP for energy and NADPH for reducing power

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of photosynthesis H2OH2O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP  ADP + P O2O2 Figure 10.5 ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light reactions convert solar E to the chemical E of ATP and NADPH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Nature of Sunlight Form of electromagnetic E, travels in waves

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Wavelength ( ) – Distance between the crests of waves – Determines the type of electromagnetic E

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electromagnetic spectrum – Entire range of electromagnetic E, or radiation Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy Figure 10.6

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Visible light spectrum – Colors of light we can see – ’s that drive photosynthesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photosynthetic Pigments: The Light Receptors Substances that absorb visible light

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Reflect light, which include the colors we see Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Figure 10.7

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Spectrophotometer – Machine that sends light through pigments and measures the fraction of light transmitted at each

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption spectrum – A graph plotting light absorption versus Figure 10.8 White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer Slit moves to pass light of selected wavelength Green light The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. The low transmittance (high absorption) reading chlorophyll absorbs most blue light. Blue light

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption spectra of chloroplast pigments – Clues to the relative effectiveness of different f/ driving photosynthesis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Absorption spectra of 3 types of pigments Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below. EXPERIMENT RESULTS Absorption of light by chloroplast pigments Chlorophyll a (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Wavelength of light (nm) Chlorophyll b Carotenoids Figure 10.9

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Action spectrum of a pigment – Effectiveness of different  of radiation in driving photosynthesis Rate of photosynthesis (measured by O 2 release) 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. (b)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings First demonstrated by Theodor W. Engelmann Aerobic bacteria Filament of alga 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 O 2 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. (c) Light in the violet-blue and red portions of the spectrum are most effective in driving photosynthesis. CONCLUSION

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chlorophyll a – Main photosynthetic pigment Chlorophyll b – Accessory pigment C CH CH 2 C C C C C CN N C H3CH3C C C C C C C C C N C C C C N Mg H H3CH3C H C CH 2 CH 3 H C H H CH 2 H CH 3 C O O O O O CHO in chlorophyll a 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 Figure 10.10

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other accessory pigments – Absorb different s of light and pass the E to chlorophyll a

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Excitation of Chlorophyll by Light When a pigment absorbs light it goes f/ a ground state to an excited state (unstable) Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground state Photon e–e– Figure A

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Isolated chlorophyll fluoresce Figure B

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Photosystem Composed of a reaction center surrounded by a number of light-harvesting complexes Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) Figure e–e–

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light-harvesting complexes – Pigment molecules bound to proteins – Funnel the E of photons of light to the reaction center

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings When a reaction-center chlorophyll molecule absorbs E – Electrons gets bumped up to a primary e - acceptor

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Thylakoid membrane – 2 types of photosystems, I and II

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Noncyclic Electron Flow Primary pathway

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Produces NADPH, ATP, and O 2 Figure Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP + ADP CALVIN CYCLE CO 2 H2OH2O O2O2 [CH 2 O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e–e– e–e– O2O2 + H2OH2O 2 H + Light ATP Primary acceptor Fd e e–e– NADP + reductase Electron Transport chain Electron transport chain P700 Light NADPH NADP H + + H

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mill makes ATP e–e– e–e– e–e– e–e– e–e– Photon Photosystem II Photosystem I e–e– e–e– NADPH Photon Figure 10.14

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cyclic e - flow – Only photosystem I is used – Only ATP is produced Primary acceptor Pq Fd Cytochrome complex Pc Primary acceptor Fd NADP + reductase NADPH ATP Figure Photosystem II Photosystem I NADP +

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis in Chloroplasts v. Mitochondria Chloroplasts and mitochondria – Generate ATP by the same basic mechanism: chemiosmosis – Use different sources of E to accomplish this

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Spatial organization of chemiosmosis Key Higher [H + ] Lower [H + ] Mitochondrion Chloroplast MITOCHONDRION STRUCTURE Intermembrance space Membrance Matrix Electron transport chain H+H+ Diffusion Thylakoid space Stroma ATP H+H+ P ADP+ ATP Synthase CHLOROPLAST STRUCTURE Figure 10.16

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In both – Redox reactions of e - transport chains generate a H + gradient across membrane ATP synthase – Uses proton-motive force to form ATP

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Light reactions and chemiosmosis LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H2OH2O CO 2 Cytochrome complex O2O2 H2OH2O O2O2 1 1⁄21⁄2 2 Photosystem I Light THYLAKOID SPACE (High H + concentration) STROMA (Low H + concentration) Thylakoid membrane ATP synthase Pq Pc Fd NADP + reductase NADPH + H + NADP + + 2H + To Calvin cycle ADP P ATP 3 H+H+ 2 H + +2 H + 2 H + Figure 10.17

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Calvin cycle Uses ATP and NADPH to convert CO 2 to sugar Similar to the citric acid cycle Occurs in the stroma

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3 phases – Carbon fixation – Reduction – Regeneration of CO 2 acceptor

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Calvin cycle (G3P) Input (Entering one at a time) CO 2 3 Rubisco Short-lived intermediate 3 PP P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P6 P 6 1,3-Bisphoglycerate 6 NADPH 6 NADPH + 6 P P 6 Glyceraldehyde-3-phosphate (G3P) 6 ATP 3 ATP 3 ADP CALVIN CYCLE P 5 P 1 G3P (a sugar) Output Light H2OH2O CO 2 LIGHT REACTION ATP NADPH NADP + ADP [CH 2 O] (sugar) CALVIN CYCLE Figure O2O2 6 ADP Glucose and other organic compounds Phase 1: Carbon fixation Phase 2: Reduction Phase 3: Regeneration of the CO 2 acceptor (RuBP)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alternative mechanisms of carbon fixation have evolved in hot, arid climates

Copyright © 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 O 2 to build up

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Photorespiration: An Evolutionary Relic? O 2 substitutes for CO 2 in the active site of the enzyme rubisco Photosynthetic rate is reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C 4 Plants Minimize photorespiration – Incorporate CO 2 into four carbon compounds in mesophyll cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 4 carbon compounds in bundle sheath cells  release CO 2  CO 2 Calvin cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C 4 leaf anatomy and the C 4 pathway CO 2 Mesophyll cell Bundle- sheath cell Vein (vascular tissue) Photosynthetic cells of C 4 plant leaf Stoma Mesophyll cell C 4 leaf anatomy PEP carboxylase Oxaloacetate (4 C) PEP (3 C) Malate (4 C) ADP ATP Bundle- Sheath cell CO 2 Pyruate (3 C) CALVIN CYCLE Sugar Vascular tissue Figure CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CAM Plants Open their stomata at night, CO 2  organic acids

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings During the day, stomata close – CO 2 is released from the organic acids for use in the Calvin cycle

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CAM pathway is similar to the C 4 pathway Spatial separation of steps. In C 4 plants, carbon fixation and the Calvin cycle occur in different types of cells. (a) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times. (b) Pineapple Sugarcane Bundle- sheath cell Mesophyll Cell Organic acid CALVIN CYCLE Sugar CO 2 Organic acid CALVIN CYCLE Sugar C4C4 CAM CO 2 incorporated into four-carbon organic acids (carbon fixation) Night Day 1 2 Organic acids release CO 2 to Calvin cycle Figure 10.20

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Review Light reactions: Are carried out by molecules in the thylakoid membranes Convert light energy to the chemical energy of ATP and NADPH Split H 2 O and release O 2 to the atmosphere Calvin cycle reactions: Take place in the stroma Use ATP and NADPH to convert CO 2 to the sugar G3P Return ADP, inorganic phosphate, and NADP+ to the light reactions O2O2 CO 2 H2OH2O Light Light reaction Calvin cycle NADP + ADP ATP NADPH + P 1 RuBP 3-Phosphoglycerate Amino acids Fatty acids Starch (storage) Sucrose (export) G3P Photosystem II Electron transport chain Photosystem I Chloroplast Figure 10.21

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Organic compounds produced by photosynthesis – Provide the E and building material for ecosystems