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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Melvin Calvin - American biochemist who his elucidated the mechanism by which carbon dioxide is incorporated into green plants, for which he received the 1961 Nobel Prize for Chemistry. In the Calvin Cycle, he described the "dark reactions" of photosynthesis occuring through the night turning carbon dioxide into sugar.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.1 Sunlight consists of a spectrum of colors, visible here in a rainbow

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.2 Photoautotrophs (a) Plants (b) Multicellular algae (c) Unicellular protist 10  m 40  m (c) Cyanobacteria 1.5  m (d) Pruple sulfur bacteria 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).

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.3 Focusing in on the location of photosynthesis in a plant Mesophyll cell Mesophyll Vein Stomata CO 2 O2O2 Chloroplast 5 µm 1 µm Outer membrane Intermembrane space Inner membrane ThylakoidThylakoid Space Granum Storma Leaf cross section

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tracking atoms through photosynthesis 6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6H2O6H2O 6O26O2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle Light LIGHT REACTIONS Chloroplast H2OH2O

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle ATP NADPH O2O2 H2OH2O Light LIGHT REACTIONS Chloroplast

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CO 2 CALVIN CYCLE O2O2 [CH 2 O] (sugar) NADP  ADP + P i An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle H2OH2O Light LIGHT REACTIONS Chloroplast ATP NADPH

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The electromagnetic spectrum 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings TECNIQUE A spectrophotometer measures the relative amounts of light of different wavelengths absorbed and transmitted by a pigment solution. 2 The transmitted light strikes a photoelectric tube, which converts the light energy to electricity. 3 4 The electrical current is measured by a galvanometer. The meter indicates the fraction of light transmitted through the sample, from which we can determine the amount of light absorbed. White light is separated into colors (wavelengths) by a prism. 1 One by one, the different colors of light are passed through the sample (chlorophyll in this example). Green light and blue light are shown here. APPLICATION An absorption spectrum is a visual representation of how well a particular pigment absorbs different wavelengths of visible light. Absorption spectra of various chloroplast pigments help scientists decipher each pigment’s role in a plant. Research Method Determining an Absorption Spectrum

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings See Figure 10.9a for absorption spectra of three types of chloroplast pigments. Result 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 indicates that chlorophyll absorbs most blue light. Blue light

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inquiry Which wavelengths of light are most effective in driving photosynthesis? 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 Chlorophyll b Carotenoids (a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments. Wavelength of light (nm)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 A mechanical analogy for the light reactions Mill makes ATP e–e– e–e– e–e– e–e– e–e– Photon Photosystem II Photosystem I e–e– e–e– NADPH Photon

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C4 carbon fixation is one of three biochemical mechanisms, along with C3 and CAM photosynthesis, used in carbon fixation. C4 carbon fixation is an elaboration of C3 pathways that allows more efficient use of scarce CO2. CAM Photosynthesis (also called crassulacean acid metabolism) is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions.

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 CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings C 4 and CAM photosynthesis compared Organic acids release CO 2 to Calvin cycle 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 CO 2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 reactions 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