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PHOTOSYNTHESIS

PHOTOSYNTHESIS. YOU MUST KNOW…. HOW PHOTOSYSTEMS CONVERT SOLAR ENERGY TO CHEMICAL ENERGY HOW LINEAR ELECTRON FLOW IN THE LIGHT REACTIONS RESULTS IN THE FORMATION OF ATP, NADPH, AND O 2 HOW CHEMIOSMOSIS GENERATES ATP IN THE LIGHT REACTIONS. YOU MUST KNOW….

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PHOTOSYNTHESIS

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  1. PHOTOSYNTHESIS

  2. YOU MUST KNOW… • HOW PHOTOSYSTEMS CONVERT SOLAR ENERGY TO CHEMICAL ENERGY • HOW LINEAR ELECTRON FLOW IN THE LIGHT REACTIONS RESULTS IN THE FORMATION OF ATP, NADPH, AND O2 • HOW CHEMIOSMOSIS GENERATES ATP IN THE LIGHT REACTIONS

  3. YOU MUST KNOW… • HOW THE CALVIN CYCLE USES THE ENERGY MOLECULES OF THE LIGHT REACTIONS TO PRODUCE G3P • THE METABOLIC ADAPTATIONS OF C4 AND CAM PLANTS TO ARID, DRY REGIONS

  4. CONCEPT 10.1 • PHOTOSYNTHESIS CONVERTS LIGHT ENERGY TO THE CHEMICAL ENERGY OF FOOD

  5. AUTOTROPHS – PRODUCERS, SELF FEEDERSOURCE OF ORGANIC COMPOUNDS • HETEROTROPHS – CONSUMER, LIVE ON COMPOUNDS PRODUCED BY OTHER ORGANISMS • HETEROTROPHS INCLUDE THE DECOMPOSERS AND ARE DEPENDENT ON PHOTOSYNTHESIS FOR FOOD AND OXYGEN

  6. CHLOROPLASTS • SITES FOR PHOTOSYNTHESIS • MAKE UP THE MESOPHYLL TISSUE FOUND IN THE INTERIOR OF THE LEAF

  7. STROMA – ENCLOSED BY 2 MEMBRANES, A DENSE FLUID-FILLED AREA • STROMA CONTAINS INTERCONNECTED MEMBRANOUS SACS CALLED THYLAKOIDS • CHLOROPHYLL – LOCATED IN THE THYLAKOID MEMBRANES AND IS THE LIGHT-ABSORBING PIGMENT

  8. STOMATA • TINY PORES ON THE EXTERIOR OF THE LOWER EPIDERMIS OF A LEAF • CARBON DIOXIDE ENTERS AND OXYGEN AND WATER VAPOR EXIT THE LEAF

  9. PHOTOSYNTHESIS 6 CO2 + 6 H2O + LIGHT  C6H12O6 + 6 O2 • OXYGEN WE BREATHE IS FROM SPLITTING OF A WATER MOLECULE • WATER IS SPLIT FOR ITS ELECTRONS, WHICH ARE TRANSFERRED ALONG WITH HYDROGEN IONS FROM WATER TO CARBON DIOXIDE, REDUCING IT TO SUGAR • PROCESS REQUIRES ENERGY (ENDERGONIC) WHICH IS PROVIDED FROM THE SUN • PROCESS IS 2 STAGES

  10. LIGHT REACTIONS • OCCURS IN THYLAKOID MEMBRANES WHERE SOLAR ENERGY IS CONVERTED TO CHEMICAL ENERGY • LIGHT IS ABSORBED BY CHLOROPHYLL AND DRIVES THE TRANSFER OF ELECTRONS FROM WATER TO NADP+, FORMING NADPH • WATER IS SPLIT & OXYGEN IS RELEASED • ATP IS GENERATED, USING CHEMIOSMOSIS TO POWER THE ADDITION OF A PHOSPHATE GROUP TO ADP (PHOTOPHOSPHORYLATION). • NET PRODUCTS ARE NADPH (STORES ELECTRONS), ATP, AND OXYGEN

  11. CALVIN CYCLE • OCCURS IN THE STROMA • CO2 FROM THE AIR IS INCORPORATED INTO ORGANIC MOLECULES IN CARBON FIXATION • CALVIN CYCLE USED THE FIXED CARBON & NADPH & ATP FROM THE LIGHT REACTION IN THE FORMATION OF NEW SUGARS

  12. CONCEPT 10.2 • THE LIGHT REACTIONS CONVERT SOLAR ENERGY TO THE CHEMICAL ENERGY OF ATP AND NADPH

  13. LIGHT IS MADE UP OF PARTICLES CALLED PHOTONS - IT HAS A FIXED QUANTITY OF ENERGY • PIGMENTS – CHLOROPHYLL ABSORBS VIOLET-BLUE AND RED LIGHT WHILE REFLECTING GREEN LIGHT • ABSORPTION SPECTRUM – A GRAPH PLOTTING A PIGMENT’S LIGHT ABSORPTION VS. WAVELENGTH • ACTION SPECTRUM – GRAPHS THE EFFECTIVENESS OF DIFFERENT WAVELENGTHS OF LIGHT IN DRIVING PHOTOSYNTHESIS

  14. PHOTOSYSTEMS • PHOTONS OF LIGHT ARE ABSORBED BY CERTAIN GROUPS OF PIGMENT MOLECULES IN THE THYLAKOID MEMBRANE OF CHLOROPLASTS

  15. LIGHT-HARVESTING COMPLEX • MADE UP OF MANY CHLOROPHYLL AND CAROTENOID MOLECULES FOR GATHERING LIGHT EFFECTIVELY • WHEN A PHOTON IS ABSORBED, ONE OF THE ELECTRONS IS RAISED TO AN ORBITAL OF HIGHER POTENTIAL ENERGY AND THE CHLOROPHYLL IS IN AN “EXCITED” STATE

  16. THE ENERGY IS TRANSFERRED TO THE REACTION CENTER OF THE PHOTOSYSTEM • THE CENTER CONSISTS OF 2 CHLOROPHYLL a MOLECULES, WHICH DONATE THE ELECTRONS TO THE SECOND MEMBER OF THE REACTION CENTER-PRIMARY ELECTRON ACCEPTOR • THE ENERGY TRANSFER FROM THE REACTION CENTER TO THE PRIMARY ELECTRON ACCEPTOR IS THE FIRST STEP OF THE LIGHT REACTIONS • CONVERSION OF LIGHT ENERGY TO CHEMICAL ENERGY OCCURS

  17. PHOTOSYSTEMS I AND II • PS I IS DESIGNATED P700 BECAUSE THE CHLOROPHYLL a BEST ABSORBS RED LIGHT OF THIS WAVELENGTH THE BEST • PS II IS DESIGNATED P680 • THE KEY IS A FLOW OF ELECTRONS THROUGH THE PHOTOSYSTEMS IN THE THYLAKOID MEMBRANE, A PROCESS CALLED LINEAR NONCYCLIC) ELECTRON FLOW • SEE HANDOUTS

  18. CYCLIC ELECTRON FLOW • USES A SHORT CIRCUIT OF LINEAR ELECTRON FLOW BY CYCLING THE EXCITED ELECTRONS BACK TO THEIR ORIGINAL STARTING POINT IN PS I • CYCLIC ELECTRON FLOW PRODUCES ATP BY CHEMIOSMOSIS BUT NO NADPH IS PRODUCED AND NO OXYGEN IS RELEASED

  19. CONCEPT 10.3 • THE CALVIN CYCLE USES ATP AND NADPH TO CONVERT CO2 TO SUGAR

  20. CALVIN CYCLE • CARBON ENTERS IN THE FORM OF CO2 AND LEAVES IN THE FORM OF A SUGAR • SPENDS ATP AS AN ENERGY SOURCE AND CONSUMES NADPH AS REDUCING POWER FOR ADDING HIGH ENERGY ELECTRONS TO MAKE THE SUGAR

  21. TO NET ONE MOLECULE OF G3P, THE CYCLE MUST GO THROUGH 3 ROTATIONS AND FIX 3 MOLECULES OF CO2

  22. MAJOR STEPS OF CYCLE • 3 CO2 MOLECULES ARE ATTACHED TO 3 MOLECULES OF THE 5-CARBON SUGAR RIBULOSE BISPHOSPHATE (RuBP) • THESE REACTIONS ARE CATALYZED BY THE ENZYME RUBISCO AND PRODUCE AN UNSTABLE PRODUCT THAT IMMEDIATELY SPLITS INTO 2 THREE-CARBON COMPOUNDS CALLED 3-PHOSPHOGLCERATE • CO2 HAS NOW BEEN FIXED (INTO AN ORGANIC COMPOUND

  23. THE 3-PHOSPHOGLYCERATE MOLECULES ARE PHOSPHORYLATED TO BECOME 1, 3-BISPHOSPHOGLYCERATE • 6 NADPH ARE THEN REDUCE THE 6 1,3-BISPHOSPHOGLYCERATE TO SIX GLYCERALDEHYDE-3-PHOSPHATE (G3P)

  24. ONE G3P LEAVES THE CYCLE TO BE USED BY THE PLANT CELL • TWO G3P MOLECULES CAN COMBINE TO FORM GLUCOSE • RuBP IS REGENERATED AS THE 5 G3Ps ARE REWORKED INTO 3 OF THE STARTING MOLECULES WITH THE EXPENDITURE OF 3 ATP MOLECULES

  25. ENERGY NEEDED TO NET ONE G3P • 9 MOLECULES OF ATP ARE CONSUMED ALONG WITH 6 MOLECULES OF NADPH (BOTH REPLENISHED BY THE LIGHT REACTIONS)

  26. CONCEPT 10.4 • ALTERNATIVE MECHANISMS OF CARBON FIXATION HAVE EVOLVED IN HOT, ARID CLIMATES

  27. CO2 ENTERS THE LEAF THROUGH THE STOMATA, THE SAME PORE THAT WATER EXITS THE LEAF IN TRANSPIRATION

  28. C3 PLANTS • ON HOT, DRY DAYS C3 PLANTS PRODUCE LESS SUGAR BECAUSE OF DECLINING LEVELS OF CO2 IN THE LEAF STARVES THE CALVIN CYCLE • STOMATA CLOSES TO CONSERVE WATER • RUBISCO CAN BIND O2 IN PLACE OF CO2 • CAUSES THE OXIDATION OF RuBP RESULTING IN A LOSS OF ENERGY AND CAROBN FOR THE PLANT (CALLED PHOTORESPIRATION) • THIS CAN DRAIN AWAY AS MUCH AS 50% OF THE CARBON FIXED BY THE CALVIN CYCLE

  29. C4 PLANTS • HAVE 2 TYPES OF PHOTOSYNTHETIC CELLS • BUNDLE-SHEATH CELL – GROUPED AROUND THE LEAF’S VEINS • MESOPHYLL CELLS – DISPERSED ELSEWHERE AROUND THE LEAF

  30. C4 PLANTS • CO2 IS ADDED TO PHOSPHOENOLPYRUVATE (PEP) TO FORM THE FOUR-CARBON COMPOUND OXALOACETATE • REACTION IS CATALYZED BY PEP CARBOXYLASE WHICH DOES NOT COMBINE WITH O2 AND DOES NOT PARTICIPATE IN PHOTORESPIRATION • CARBON IS NOW FIXED

  31. MESOPHYLL CELLS EXPORT THE OXALOACETATE TO THE BUNDLE-SHEATH CELLS, WHICH BREAK IT DOWN AND RELEASE CO2 • CO2 IN THE BUNDLE-SHEATH CELLS IS THEN CONVERTED INTO CARBOHYDRATES THROUGH THE NORMAL CALVIN CYCLE • PHOTORESPIRATION IS REDUCED SINCE CO2 CONCENTRATION IS HIGH AND RUBISCO BINDS TO IT INSTEAD OF OXYGEN

  32. CAM PHOTOSYNTHESIS • ANOTHER ADAPTATION TO HOT, DRY CLIMATES • PLANTS KEEP THEIR STOMATA CLOSED DURING THE DAY • AT NIGHT, THE STOMATA OPEN AND CO2 IS FIXED IN ORGANIC ACIDS AND STORED IN VACUOLES • PHOTOSYNTHESIS CONTINUES DURING THE DAY • LATER ENTERS THE CALVIN CYCLE

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