Chapter 10(2)

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[object Object],[object Object],Figure 10.1

[object Object],[object Object],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

Chloroplasts: The Sites of Photosynthesis in Plants ,[object Object],[object Object],Vein Leaf cross section Figure 10.3 Mesophyll CO 2 O 2 Stomata

[object Object],[object Object],[object Object],Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

Tracking Atoms Through Photosynthesis: Scientific Inquiry ,[object Object],6 CO 2 + 12 H 2 O + Light energy  C 6 H 12 O 6 + 6 O 2 + 6 H 2 O

The Splitting of Water ,[object Object],[object Object],6 CO 2 12 H 2 O Reactants: Products: C 6 H 12 O 6 6 H 2 O 6 O 2 Figure 10.4

Photosynthesis as a Redox Process ,[object Object],[object Object]

The Two Stages of Photosynthesis: A Preview ,[object Object],[object Object],[object Object]

[object Object],H 2 O CO 2 Light LIGHT REACTIONS CALVIN CYCLE Chloroplast [CH 2 O] (sugar) NADPH NADP  ADP + P O 2 Figure 10.5 ATP

The Nature of Sunlight ,[object Object],[object Object]

[object Object],[object Object],Gamma rays X-rays UV Infrared 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 380 450 500 550 600 650 700 750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy Figure 10.6

Photosynthetic Pigments: The Light Receptors ,[object Object],[object Object]

[object Object],Light Reflected Light Chloroplast Absorbed light Granum Transmitted light Figure 10.7

[object Object],[object Object],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 1 2 3 4 0 100 0 100

[object Object],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

[object Object],[object Object],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)

[object Object],[object Object],400 500 600 700 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

[object Object],[object Object],[object Object],[object Object],C CH CH 2 C C C C C C N N C H 3 C C C C C C C C C N C C C C N Mg H H 3 C H C CH 2 CH 3 H CH 3 C H H CH 2 CH 2 CH 2 H CH 3 C O O O O O CH 3 CH 3 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

Excitation of Chlorophyll by Light ,[object Object],[object Object],Excited state Energy of election Heat Photon (fluorescence) Chlorophyll molecule Ground state Photon e – Figure 10.11 A

[object Object],[object Object],Figure 10.11 B

A Photosystem: A Reaction Center Associated with Light-Harvesting Complexes

[object Object],[object Object],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 10.12 e –

Noncyclic Electron Flow ,[object Object],[object Object]

[object Object],Figure 10.13 Photosystem II (PS II) Photosystem-I (PS I) ATP NADPH NADP + ADP CALVIN CYCLE CO 2 H 2 O O 2 [CH 2 O] (sugar) LIGHT REACTIONS Light Primary acceptor Pq Cytochrome complex PC e P680 e – e – O 2 + H 2 O 2 H + Light ATP Primary acceptor Fd e e – NADP + reductase Electron Transport chain Electron transport chain P700 Light NADPH NADP + + 2 H + + H + 1 5 7 2 3 4 6 8

[object Object],Mill makes ATP ATP e – e – e – e – e – Photon Photosystem II Photosystem I e – e – NADPH Photon Figure 10.14

Cyclic Electron Flow ,[object Object],[object Object]

[object Object],[object Object],[object Object],Primary acceptor Pq Fd Cytochrome complex Pc Primary acceptor Fd NADP + reductase NADPH ATP Figure 10.15 Photosystem II Photosystem I NADP +

A Comparison of Chemiosmosis in Chloroplasts and Mitochondria ,[object Object],[object Object],[object Object]

[object Object],[object Object],Key Higher [H + ] Lower [H + ] Mitochondrion Chloroplast MITOCHONDRION STRUCTURE Intermembrance space Membrance Matrix Electron transport chain H + Diffusion Thylakoid space Stroma ATP H + P ADP+ ATP Synthase CHLOROPLAST STRUCTURE Figure 10.16

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[object Object],LIGHT REACTOR NADP + ADP ATP NADPH CALVIN CYCLE [CH 2 O] (sugar) STROMA (Low H + concentration) Photosystem II LIGHT H 2 O CO 2 Cytochrome complex O 2 H 2 O O 2 1 1 ⁄ 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 + 2 H + +2 H + 2 H + Figure 10.17

[object Object],Phase 1: Carbon fixation Phase 2: Reduction Phase 3: Regeneration of the CO 2 acceptor (RuBP) (G3P) Input (Entering one at a time) CO 2 3 Rubisco Short-lived intermediate 3 P P 3 P P Ribulose bisphosphate (RuBP) P 3-Phosphoglycerate P 6 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 H 2 O CO 2 LIGHT REACTION ATP NADPH NADP + ADP [CH 2 O] (sugar) CALVIN CYCLE Figure 10.18 O 2 6 ADP Glucose and other organic compounds

Photorespiration: An Evolutionary Relic? ,[object Object],[object Object],[object Object]

C 4 Plants ,[object Object],[object Object]

[object Object],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 10.19 CO 2

CAM Plants ,[object Object],[object Object]

[object Object],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 CO 2 Organic acid CALVIN CYCLE Sugar C 4 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

The Importance of Photosynthesis: A Review ,[object Object],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 O 2 CO 2 H 2 O 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

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