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 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

PHOTOSYNTHESIS NET REACTION SUNLIGHT 6 CO2 + 6 H20 C6H12O6 + 6 O2 CHLOROPHYLL PHOTOSYNTHESIS ACTUAL REACTION SUNLIGHT 6 CO2 + 12 H20 C6H12O6 + 6 O2 + 6 H2O CHLOROPHYLL DISCOVERED THROUGH THE USE OF O-18 TAGGED WATER

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)

Chlorophyll a absorption and efficiency of Photosynthesis

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

Chloroplast Structure

CHLOROPLAST STRUCTURE THYLAKOIDS GRANA STROMA CHLOROPLAST MEMBRANE

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

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

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

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

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

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

Photosystem I and II

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

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

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

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