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PHOTOSYNTHESIS THREE PHASE REACTION

PHOTOSYNTHESIS THREE PHASE REACTION. LIGHT ABSORBTION (CHLOROPHYLL) LIGHT REACTION (LIGHT DEPENDENT) DARK REACTION (LIGHT INDEPENDENT). Green Plants and Photosynthesis All of our food ultimately results from the process of photosynthesis

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PHOTOSYNTHESIS THREE PHASE REACTION

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  1. PHOTOSYNTHESISTHREE PHASE REACTION • LIGHT ABSORBTION(CHLOROPHYLL) • LIGHT REACTION (LIGHT DEPENDENT) • DARKREACTION (LIGHT INDEPENDENT)

  2. Green Plants and Photosynthesis All of our food ultimately results from the process of photosynthesis in green plants and algae. The pigment chlorophyll is responsible for the green color of plants as well as their ability to photosynthesize. In common terrestrial plants photosynthesis is usually carried out in the leaves, although it can also occur in the stem or other parts of the plant. Dr. C.E. Jeffree, Oxford Scientific Films

  3. PHOTOSYNTHESISNET REACTION SUNLIGHT 6 CO2 + 6 H20 C6H12O6 + 6 O2 CHLOROPHYLL PHOTOSYNTHESISACTUAL REACTION SUNLIGHT 6 CO2 + 12 H20 C6H12O6 + 6 O2 + 6 H2O CHLOROPHYLL DISCOVERED THROUGH THE USE OF O-18 TAGGED WATER

  4. LIGHT ABSORBTION BY CHLOROPHYLL • CHLOROPHYLL A IS THE PRIMARY PHOTOSYNTHETIC PIGMENT • CHLOROPHYLL B, CAROTENE, PHYCOBILINS, XANTHROPHYLL, AND OTHER PIGMENTS ARE ACCESSORY PIGMENTS • LOCATED IN THYLAKOID MEMBRANE OF THE CHLOROPLAST • ABSORBS RED AND BLUE LIGHT, REFLECTS GREEN LIGHT • ACCESSORY PIGMENTS TRAP GREEN AND YELLOW LIGHT AND TRANSFER IT TO CHLOROPHYLL A (allow greater use of available energy)

  5. Chlorophyll a absorption and efficiency of Photosynthesis

  6. STRUCTURE OF CHLOROPLAST • GRANA ARRANGED IN STACKS TO MAXIMIZE EXPOSURE TO LIGHT - LIGHT REACTIONS OCCUR HERE. • SHAPE OF GRANA MAXIMIZES SURFACE AREA FOR PHOTOSYNTHESIS • GRANA SURROUNDED BY STROMA - PERMITS EASY DIFFUSION OF PHOTOSYNTHETIC PRODUCTS • PRODUCTS MOVE BACK AND FORTH BETWEEN THE LUMEN AND THE STROMA • STROMA IS A PROTEIN RICH SOLUTION IN WHICH DARK REACTIONS OCCUR

  7. Chloroplast Structure

  8. CHLOROPLAST STRUCTURE THYLAKOIDS GRANA STROMA CHLOROPLAST MEMBRANE

  9. Chloroplasts in Onion Root CellsChloroplasts are minute, green, spherical structures that are essential to the process of photosynthesis. The chlorophyll molecule, a very complex organic molecule composed primarily of magnesium, carbon, and hydrogen, regulates the absorption of the red, violet, and blue portions of the visible light spectrum. Richard Kirby, Oxford Scientific Films

  10. LIGHT REACTIONS • TWO PARTS • CONVERSION OF SUNLIGHT TO ELECTRICAL ENERGY (ELECTRON TRANSPORT) • ELECTRICAL ENERGY IS THEN CONVERTED TO CHEMICAL ENERGY STORED IN BONDS

  11. PHOTOSYSTEM II • LIGHT STRIKES CHLOROPHYLL - ELECTRONS ABSORB PHOTON OF LIGHT ENERGY AND BECOME “EXCITED” • “EXCITED” ELECTRONS MOVE TO ELECTRON ACCEPTORS WHERE THEY MOVE TO A LOWER ENERGY STATE (ELECTRON TRANSPORT CHAIN) TRANSFERED TO PHOTOSYSTEM I

  12. PHOTOSYSTEM I • LIGHT ALSO STRIKES CHLOROPHYLL IN PHOTOSYSTEM I WHICH ALSO MOVE ALONG AN ELECTRON TRANSPORT CHAIN • ELECTRONS REPLACED BY THOSE FROM PHOTOSYSTEM II • ELECTRONS ARE PICKED UP BY NADP TO FORM NADP- -WATER IS SPLIT INTO TWO H+ IONS, TWO ELECTRONS, AND AN OXYGEN ATOM • The H + ions are used to reduce NADP to form NADPH2 • The electrons go to photosystem II • The oxygen atom combines with another oxygen to form O2 • NADPH2 goes to stroma to be used in DARK REACTIONS

  13. PHOTOSYSTEM I ATP ADP + P SUN cytochromes - e - e ELECTRON ACCEPTORS - - e e - e - CHLOROPHYLL e ELECTRON TRANSPORT CHAIN ADP + P ATP

  14. NADPH2 PHOTOSYSTEM II O O2 -- NADP ELECTRON TRANSPORT CHAIN H20 2 H+ 2 e- ADP+ P ATP CHLOROPHYLL II CHLOROPHYLL I ELECTRON TRANSPORT CHAIN

  15. Photosystem I and II

  16. CHEMIOSMOSIS • DIFFUSION OF CHEMICALS THROUGH THE MEMBRANE RESULTING IN PRODUCTION OF ATP • ELECTRONS MOVE ALONG ELECTRON TRANSPORT CHAIN FROM HIGH TO LOW CONCENTRATION • CONCENTRATION OF HYDROGEN IONS IS HIGHER INSIDE THE LUMEN THAN IN THE STROMA • ELECTROCHEMICAL ENERGY IS GENERATED BY THE MOVEMENT OF IONS ACCROSS THE MEMBRANE • ENERGY IS USED TO PHOSPHORYLATE ADP TO FORM ATP (using ATP synthetase) • ATP IS THEN USED IN CARBON FIXATION IN DARK REACTIONS

  17. DARK REACTIONSCALVIN CYCLE (C3) • DOES NOT REQIRE LIGHT ENERGY • USES ENERGY STORED IN LIGHT REACTIONS IN THE FORM OF ATP AND NADPH2 • INVOLVES FIXATION OF CO2 INTO CARBON COMPOUNDS • OCCURS IN MOST PLANT SPECIES IN MODRATE CLIMATES • DIVIDED INTO FOUR BASIC STEPS

  18. FOUR STAGES OF THE DARK REACTIONS • CO2 DIFFUSES INTO THE STROMA AND AN ENZYME IN THE THYLAKOID BINDS IT TO A 5-CARBON RDP (RuBP) FORMING AN UNSTABLE 6-CARBON MOLECULE • THIS 6-CARBON MOLECULE SPLITS TO FORM TWO 3-CARBON PGA MOLECULES • PGA IS CHANGED TO PGAL BY PHOSPHORYLATON USING ATP AND THE ADDITION OF H FROM NADPH2 • TWO PGAL MOLECULES COMBINE TO FORM A 6-CARBON COMPOUND FDP (fructose diphosphate) WHICH EITHER IS CONVERTED INTO GLUCOSE (1 FOR EVERY 6 CO2 FIXED) OR USED TO REGENERATE RDP SO THE CYCLE CAN CONTINUE

  19. CALVIN CYCLE (C3) ATP ADP CO2 PGA 3-C PGAL NADPH2 NADP 6-C ATP ADP PGAL PGA 3-C NADPH2 NADP RDP 5-C FDP 6-C INTERMEDIATE COMPOUNDS ATP RP 5-C ADP GLUCOSE

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