Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 10 Photosynthesis

Copyright © 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 Vein Leaf cross section Figure 10.3 Mesophyll CO 2 O2O2 Stomata

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chloroplasts – Are the organelles in which photosynthesis occurs – 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 Tracking Atoms Through Photosynthesis: Scientific Inquiry Photosynthesis is summarized as 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 Photosynthesis as a Redox Process Photosynthesis is a redox process – Water is oxidized, carbon dioxide is reduced LEO says GER Lose electrons = oxidized Gain electrons = reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An 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 Concept 10.2: The light reactions convert solar energy to the chemical energy of ATP and NADPH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Wavelength – Is the distance between the crests of waves – Determines the type of electromagnetic energy

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The electromagnetic spectrum – Is the entire range of electromagnetic energy, 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 – 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 An absorption spectrum – Is a graph plotting light absorption versus wavelength 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 The absorption spectra of three types of pigments in chloroplasts 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 The action spectrum of a pigment – Profiles the relative effectiveness of different wavelengths 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 The action spectrum for photosynthesis – Was 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 The light reactions and chemiosmosis: the organization of the thylakoid membrane 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 Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin cycle – Is similar to the citric acid cycle – Occurs in the stroma

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Calvin cycle has three phases – Carbon fixation – Reduction – Regeneration of the CO 2 acceptor

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The 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 Concept 10.4: 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 oxygen to build up

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C 4 Plants C 4 plants minimize the cost of photorespiration – By incorporating CO 2 into four carbon compounds in mesophyll cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings These four carbon compounds – Are exported to bundle sheath cells, where they release CO 2 used in the 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 CAM plants – Open their stomata at night, incorporating CO 2 into organic acids

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The 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 The Importance of Photosynthesis: A Review A review of photosynthesis 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