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… HOW THE CALVIN CYCLE USES THE ENERGY MOLECULES OF THE LIGHT REACTIONS TO PRODUCE G3P THE METABOLIC ADAPTATIONS OF C 4 AND CAM PLANTS TO ARID, DRY REGIONS

CONCEPT 10.1 PHOTOSYNTHESIS CONVERTS LIGHT ENERGY TO THE CHEMICAL ENERGY OF FOOD

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

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

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

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

PHOTOSYNTHESIS 6 CO H 2 O + LIGHT  C 6 H 12 O O 2 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

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

CHEMIOSMOSIS MOVEMENT OF IONS ACROSS A SELECTIVELY PERMEABLE MEMBRANE, DOWN THEIR ELECTROCHEMICAL GRADIENT IT RELATES TO THE GENERATION OF ATP BY THE MOVEMENT OF HYDROGEN IONS ACROSS A MEMBRANE FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION.

CALVIN CYCLE OCCURS IN THE STROMA CO 2 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

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

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

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

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

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

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

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

CONCEPT 10.3 THE CALVIN CYCLE USES ATP AND NADPH TO CONVERT CO 2 TO SUGAR

CALVIN CYCLE CARBON ENTERS IN THE FORM OF CO 2 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

TO NET ONE MOLECULE OF G3P, THE CYCLE MUST GO THROUGH 3 ROTATIONS AND FIX 3 MOLECULES OF CO 2

MAJOR STEPS OF CYCLE 3 CO 2 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- PHOSPHOGLYCERATE CO 2 HAS NOW BEEN FIXED (INTO AN ORGANIC COMPOUND

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

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

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

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

CO 2 ENTERS THE LEAF THROUGH THE STOMATA, THE SAME PORE THAT WATER EXITS THE LEAF IN TRANSPIRATION

C 3 PLANTS ON HOT, DRY DAYS C 3 PLANTS PRODUCE LESS SUGAR BECAUSE OF DECLINING LEVELS OF CO 2 IN THE LEAF STARVING THE CALVIN CYCLE STOMATA CLOSES TO CONSERVE WATER RUBISCO CAN BIND O 2 IN PLACE OF CO 2 CAUSES THE OXIDATION OF RuBP RESULTING IN A LOSS OF ENERGY AND CARBON FOR THE PLANT (CALLED PHOTORESPIRATION) THIS CAN DRAIN AWAY AS MUCH AS 50% OF THE CARBON FIXED BY THE CALVIN CYCLE

C 4 PLANTS HAVE 2 TYPES OF PHOTOSYNTHETIC CELLS BUNDLE-SHEATH CELL – GROUPED AROUND THE LEAF’S VEINS MESOPHYLL CELLS – DISPERSED ELSEWHERE AROUND THE LEAF

C 4 PLANTS CO 2 IS ADDED TO PHOSPHOENOLPYRUVATE (PEP) TO FORM THE FOUR-CARBON COMPOUND OXALOACETATE REACTION IS CATALYZED BY PEP CARBOXYLASE WHICH DOES NOT COMBINE WITH O 2 AND DOES NOT PARTICIPATE IN PHOTORESPIRATION CARBON IS NOW FIXED

MESOPHYLL CELLS EXPORT THE OXALOACETATE TO THE BUNDLE- SHEATH CELLS, WHICH BREAK IT DOWN AND RELEASE CO 2 CO 2 IN THE BUNDLE-SHEATH CELLS IS THEN CONVERTED INTO CARBOHYDRATES THROUGH THE NORMAL CALVIN CYCLE PHOTORESPIRATION IS REDUCED SINCE CO 2 CONCENTRATION IS HIGH AND RUBISCO BINDS TO IT INSTEAD OF OXYGEN

CAM PHOTOSYNTHESIS ANOTHER ADAPTATION TO HOT, DRY CLIMATES PLANTS KEEP THEIR STOMATA CLOSED DURING THE DAY AT NIGHT, THE STOMATA OPEN AND CO 2 IS FIXED IN ORGANIC ACIDS AND STORED IN VACUOLES PHOTOSYNTHESIS CONTINUES DURING THE DAY LATER ENTERS THE CALVIN CYCLE