1 / 34

Chapter 10~ Photosynthesis

Chapter 10~ Photosynthesis. + water + energy  glucose + oxygen. carbon dioxide. light energy. . 6CO 2. +. 6H 2 O. +. +. 6O 2. C 6 H 12 O 6. The chemical Pathway. reduction = endergonic. “photo” means light “synthesis” means to make. H 2 O. CO 2. N. K. P. ….

florence-vance
Download Presentation

Chapter 10~ Photosynthesis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 10~ Photosynthesis

  2. + water + energy  glucose + oxygen carbon dioxide light energy  6CO2 + 6H2O + + 6O2 C6H12O6 The chemical Pathway reduction = endergonic “photo” means light “synthesis” means to make

  3. H2O CO2 N K P … Photosynthesis ATP • Need to… • Convert light energy into chemical energy • need to get building block atomsfrom the environment • C,H,O,N,P,K,S,Mg • produce all organic moleculesneeded for growth • carbohydrates, proteins, lipids, nucleic acids

  4. The chloroplast • Sites of photosynthesis • Organelle: chloroplast • Pigment: chlorophyll • Plant cell: mesophyll • Gas exchange: stomata • Thylakoids • Stroma

  5. Photosynthesis • Light reactions • light-dependent reactions • Occurs in thylakoid • convert solar energy to chemical energy • ATP & NADPH • Oxygen is a by product • Calvin cycle • light-independent reactions • Occurs in the stroma • sugar building reactions, carbon fixation • uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6

  6. The importance of light • Pigments – absorb light of different wavelengths • Chlorophyll gives a leaf their green color • Absorb blue and red and reflect green • Two groups of pigments • In the thylakoid • Photosystem II (P680) • Photosystem I (P700)

  7. Photosystems • Two parts • Light harvesting • Made of accessory pigments • Gathers light • This will “excit” an electron • Reaction center • Made of chlorophyll a molecules • Takes energy from light harvester • donate to primary electron acceptor

  8. Light Reaction • The key is to follow the flow of the electrons through the photosystems in the thylakoid

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

  10. Photosystem II • Absorbs light energy, excited electron • Donate an electron to the primary electron acceptor • Oxidized and requires a new electron • Water splits forming two hydrogen ions, two electrons and an oxygen atom • Electrons from water replenish lost electron • An oxygen molecules is made and released as a by product • ETC • Original excited electron transported to photosystem I through ETC • This creates a gradient, that chemiosmosis uses to phosphorylate ADP to ATP • ATP is used in calvin for carbohydrate formation • Photosystem I • Light energy also activates here causing the donation of electron to a primary electron acceptor • Electrons are replaced by electrons in PSII • The PS I electrons reduces NADP+ to NADPH • NADPH is used for the calvin cycle • This is linear or noncyclic flow

  11. 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

  12. Cyclic photophosphorylation • If PS I can’t pass electron to NADP…it cycles back to PS II & makes more ATP, but no NADPH • coordinates light reactions to Calvin cycle • Calvin cycle uses more ATP than NADPH  ATP 18 ATP +12 NADPH  1 C6H12O6

  13. Calvin CycleFrom CO2 C6H12O6 • CO2 has very little chemical energy • fully oxidized • C6H12O6contains a lot of chemical energy • highly reduced • Synthesis = endergonic process • put in a lot of energy • Reduction of CO2C6H12O6proceeds in many small uphill steps • each catalyzed by a specific enzyme • using energy stored in ATP & NADPH

  14. stroma thylakoid From Light reactions to Calvin cycle • Calvin cycle • chloroplast stroma • Need products of light reactions to drive synthesis reactions • ATP • NADPH Take three rotations Or three molecules of CO2

  15. 5C 1C 3C 3C 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 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

  16. To G3P • Glyceraldehyde-3-P • end product of Calvin cycle • energy rich 3 carbon sugar • G3Pis an important intermediate • G3P  glucose   carbohydrates

  17. RuBisCo • Enzyme which fixes carbon from air • ribulose bisphosphate carboxylase • the most important enzyme in the world! • it makes life out of air! • definitely the most abundant enzyme

  18. NADP ADP Photosynthesis summary • Light reactions • produced ATP • produced NADPH • consumed H2O • produced O2as byproduct • Calvin cycle • consumed CO2 • produced G3P (sugar) • regenerated ADP • regenerated NADP

  19. 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

  20. 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

  21. 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

  22. Photosynthesis:Variations on the Theme

  23. Controlling water loss from leaves • Hot or dry days • stomates close to conserve water • guard cells • gain H2O = stomates open • lose H2O = stomates close • adaptation to living on land, but… creates PROBLEMS!

  24. O2 CO2 H2O O2 CO2 When stomates close… • Closed stomates lead to… • O2 build up  from light reactions • CO2 is depleted  in Calvin cycle • causes problems in Calvin Cycle xylem (water) phloem (sugars)  

  25. Inefficiency of RuBisCo: CO2 vs O2 • RuBisCo in Calvin cycle • carbon fixation enzyme • normally bonds Cto RuBP • CO2 is the optimal substrate • reduction of RuBP • building sugars • when O2 concentration is high • RuBisCo bonds Oto RuBP • O2 is a competitive substrate • oxidation of RuBP • breakdown sugars photosynthesis photorespiration

  26. 1C 5C 3C CO2 RuBP 5C 6C unstable intermediate ATP ADP 3C ATP PGA ADP G3P 3C NADPH NADP Calvin cycle when CO2 is abundant RuBisCo G3P to make glucose C3 plants

  27. O2 RuBP 5C 3C 2C to mitochondria ––––––– lost as CO2 withoutmaking ATP Calvin cycle when O2 is high RuBisCo photorespiration

  28. Impact of Photorespiration • Oxidation of RuBP • short circuit of Calvin cycle • loss of carbons to CO2 • can lose 50% of carbons fixed by Calvin cycle • reduces production of photosynthesis • no ATP (energy) produced • no C6H12O6 (food) produced • if photorespiration could be reduced, plant would become 50% more efficient • strong selection pressure to evolve alternative carbon fixation systems

  29. Reducing photorespiration • Separate carbon fixation from Calvin cycle • C4 plants • PHYSICALLY separate carbon fixation from Calvin cycle • different cells to fix carbon vs. where Calvin cycle occurs • store carbon in 4C compounds • different enzyme to capture CO2 (fix carbon) • PEP carboxylase • different leaf structure • CAM plants • separate carbon fixation from Calvin cycle by TIME OF DAY • fix carbon during night • store carbon in 4C compounds • perform Calvin cycle during day

  30. C4 plants • A better way to capture CO2 • 1st step before Calvin cycle, fix carbon with enzymePEP carboxylase • store as 4C compound • adaptation to hot, dry climates • have to close stomates a lot • different leaf anatomy • sugar cane, corn, other grasses… corn sugar cane

  31. CAM (Crassulacean Acid Metabolism) plants • Adaptation to hot, dry climates • separate carbon fixation from Calvin cycle by TIME • close stomates during day • open stomates during night • at night: open stomates & fix carbonin 4C “storage” compounds • in day: release CO2 from 4C acids to Calvin cycle • increases concentration of CO2 in cells • succulents, some cacti, pineapple

  32. CAM plants cacti succulents pineapple

  33. C4 vs CAM Summary solves CO2 / O2 gas exchangevs. H2O losschallenge CAM plants separate 2 steps of C fixation temporally =2 different times night vs. day C4 plants separate 2 steps of C fixation anatomically in 2 different cells

  34. Why the C3 problem? • Possibly evolutionary baggage • Rubisco evolved in high CO2 atmosphere • there wasn’t strong selection against active site of Rubisco accepting both CO2 & O2 • Today it makes a difference • 21% O2 vs. 0.03% CO2 • photorespiration can drain away 50% of carbon fixed by Calvin cycle on a hot, dry day • strong selection pressure to evolve better way to fix carbon & minimize photorespiration

More Related