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Photosynthesis

Photosynthesis. Chapter 8. Photosynthesis Overview. Energy for all life on Earth ultimately comes from photosynthesis. 6CO 2 + 12H 2 O C 6 H 12 O 6 + 6H 2 O + 6O 2 Photosynthesis is divided into: light-dependent reactions -capture energy from sunlight

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Photosynthesis

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  1. Photosynthesis Chapter 8

  2. Photosynthesis Overview Energy for all life on Earth ultimately comes from photosynthesis. 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 Photosynthesis is divided into: light-dependent reactions -capture energy from sunlight -make ATP and reduce NADP+ to NADPH carbon fixation reactions -use ATP and NADPH to synthesize organic molecules from CO2

  3. Photosynthesis takes place in chloroplasts. thylakoid membrane – internal membrane arran-ged in flattened sacs -containchlorophyll and other pigments grana – stacks of thyla- koid membranes stroma – semiliquid substance surrounding thylakoid membranes

  4. Light: absorption spectra • Photosynthesis gets energy by absorbing wavelengths of light • chlorophyll a • absorbs best in red & blue wavelengths & least in green • accessory pigments with different structures absorb light of different wavelengths • chlorophyll b, carotenoids, xanthophylls

  5. Pigments of photosynthesis • Chlorophylls & other pigments • embedded in thylakoid membrane • arranged in a “photosystem” • collection of molecules • structure-function relationship

  6. Photosystems of photosynthesis • 2 photosystems in thylakoid membrane • collections of chlorophyll molecules • act as light-gathering molecules • Photosystem II • chlorophyll a • P680 = absorbs 680nm wavelength red light • Photosystem I • chlorophyll b • P700 = absorbs 700nm wavelength red light reactioncenter antennapigments

  7. Photosystem Organization At the reaction center, the energy from the antenna complex is transferred to chlorophyll a. This energy causes an electron from chlorophyll to become excited. The excited electron is transferred from chlorophyll a to an electron acceptor. Water donates an electron to chlorophyll a to replace the excited electron.

  8. At the reaction center, the energy from the antenna complex is transferred to chlorophyll a. This energy causes an electron from chlorophyll to become excited. The excited electron is transferred from chlorophyll a to an electron acceptor. Water donates an electron to chlorophyll a to replace the excited electron.

  9. Light-Dependent Reactions Light-dependent reactions occur in 4 stages: 1. a photon of light is captured by a pigment molecule 2. energy is transferred to the reaction center; an excited electron is transferred to an acceptor molecule 3. electron transport – electrons move through carriers to reduce NADP+ 4. chemiosmosis – produces ATP

  10. Light-Dependent Reactions ATP is produced via chemiosmosis. - ATP synthaseis embedded in the thylakoid membrane -protons have accumulated in the thylakoid space -protons move into the stroma only through ATP synthase -ATP is produced from ADP + Pi

  11. Photosystem II Photosystem I ETC of Photosynthesis chlorophyll a chlorophyll b

  12. e e ETC of Photosynthesis sun 1 Photosystem IIP680chlorophyll a

  13. H H O e e H+ H H +H e- e- H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ ETC of Photosynthesis Inhale, baby! thylakoid chloroplast ATP Plants SPLIT water! 1 2 O O e e fill the e– vacancy Photosystem IIP680 chlorophyll a

  14. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ e e e e to Calvin Cycle ADP + Pi H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ ETC of Photosynthesis thylakoid chloroplast ATP 3 1 2 ATP 4 energy to buildcarbohydrates Photosystem IIP680 chlorophyll a ATP

  15. e e e e e e ETC of Photosynthesis sun fill the e– vacancy 5 e e Photosystem IP700 chlorophyll b Photosystem IIP680 chlorophyll a

  16. e e e e NADPH toCalvin Cycle ETC of Photosynthesis electron carrier 6 5 sun Photosystem IP700 chlorophyll b Photosystem IIP680 chlorophyll a $$ in the bank…reducing power!

  17. e e e e H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ ETC of Photosynthesis sun sun O to Calvin Cycle split H2O ATP

  18. Carbon Fixation Reactions To build carbohydrates, cells need: 1. energy -ATP from light-dependent reactions 2. reduction potential -NADPH from photosystem I

  19. Carbon Fixation Reactions Calvin cycle -biochemical pathway that allows for carbon fixation -occurs in the stroma -uses ATP and NADPH as energy sources -incorporates CO2into organic molecules

  20. Carbon Fixation Reactions carbon fixation – the incorporation of CO2 into organic molecules -occurs in the first step of the Calvin cycle The reaction is catalyzed byrubisco. The Calvin cycle has 3 phases: 1. carbon fixation RuBP + CO2 2 molecules PGA 2. reduction PGA is reduced to G3P 3. regeneration of RuBP G3P is used to regenerate RuBP

  21. C 3C 5C 3C 1C CO2 C 5C C 3 ATP C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 3 ADP 3C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C 6C = = C C C 6 ATP 6 NADPH H H H H H H | | | | | | – – C C C 6 NADP 6 ADP C Calvin cycle C 1. Carbon fixation 3. Regenerationof RuBP RuBP RuBisCo ribulose bisphosphate starch,sucrose,cellulose& more ribulose bisphosphate carboxylase used to makeglucose glyceraldehyde-3-P PGA G3P phosphoglycerate 2. Reduction

  22. Carbon Fixation Reactions Glucose is not a direct product of the Calvin cycle. -2 molecules of G3P leave the cycle -each G3P contains 3 carbons -2 G3P are used to produce 1 glucose in reactions in the cytoplasm During the Calvin cycle, energy is needed. The energy is supplied from: - 18 ATP molecules - 12 NADPH molecules

  23. light energy  H2O + + + O2 ATP NADPH sunlight Light Reactions H2O • produces ATP • produces NADPH • releases O2 as a waste product Energy Building Reactions NADPH ATP O2

  24. CO2 + + + + ATP NADPH C6H12O6 ADP NADP Calvin Cycle • builds sugars • uses ATP & NADPH • recycles ADP & NADP • back to make more ATP & NADPH CO2 ADP NADP SugarBuilding Reactions NADPH ATP sugars

  25. light energy  CO2 + H2O + C6H12O6 + O2 sunlight Putting it all together Plants make both: • energy • ATP & NADPH • sugars H2O CO2 ADP NADP SugarBuilding Reactions Energy Building Reactions NADPH ATP sugars O2

  26. Carbon Fixation Reactions The energy cycle: -photosynthesis uses the products of respiration as starting substrates -respiration uses the products of photosynthesis as starting substrates

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