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PhotosynthesisKeyWords

Phosphorylation-Addingphosphatetoamolecule(ADPisphosphorylatedintoATP)

Photophosphorylation-Addingofaphosphatemoleculeusinglight

Photolysis-Splitting(lysis)ofamoleculeusinglight

Hydrolysis-Splittingofamoleculeusingwater(ATPhydrolysedtoADP)

RedoxReactions-Reactionsthatinvolveoxidation(losingofelectrons)andreduction(gaining

ofelectrons)

Chloroplastisadaptedforphotosynthesisbecause;thylakoidshavelargesurfacearea=morelight

energytobeabsorbed,lotsofATPsynthasepresentinthylakoids,stromacontainsallenzymes

neededforlightindependentreactionandchloroplastenvelopekeepsreactantsfotphotosynthesis

closetoreactionsites.

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Photosynthesis (Equations, ATP and Locations)

Photosynthesis stores energy as glucose, via a series of reactions which use light to break apart

strong bonds in water molecules.

6(CO2) + 6(H2O) + Energy = C6H12O6 (glucose) + 6(O2)

Cells release energy from glucose via respiration (aerobic/anaerobic)

C6H12O6 (glucose) + 6(O2) = 6(CO2) + 6(H2O) + Energy

ATP IS IMMEDIATE SOURCE OF ENERGY IN A CELL

ATP is broken down into ADP and an inorganic P molecule using ATPase, the reaction is

exothermic (give off energy). ATP needs to be resynthesised, but the reaction is endothermic

(requires energy).

Photosynthesis occurs in the chloroplasts (small, flattened organelles). Chloroplasts have a double

membrane and contain thylakoid stacks called grana, The grana are linked together with lamellae.

Chloroplasts contain photosynthetic pigements called chlorophyll. These are found in the thylakoid

membranes and are attached to proteins. The protein and the pigment together are called

photosystems. Photosystem 1 absorbs 700nm light best and photosystem 2 absorbs 680nm light

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Non-CyclicPhotophosphorylation

OccursinPhotosystem2in4stages:

1)Lightenergyexciteselectronsinchlorophyll.Absorbedlightenergyexciteselectrons,causing

themtohaveahigherenergylevel,whichthenmovedowntheETC.

2)Photolysisofwater,producesHionsandOxygen.Usedotreplacelostelectrons,lightenergy

spiltswaterintoprotons(Hions),electronsandOxygen.H20=(2H+)+(1/2O2)

3)EnergyfromexcitedelectronsmakeATP.ExcitedelectronstraveldowntheETCandthe

electronsloseenergy.Thislostenergyisusedtotransportprotonsintothethylakoid,forminga

protongradientacrossthemembrane.TheenergyfromthismovementofphosphatescausesATP

synthasetoresynthesisADPbacktoATP.

4)GeneratesreducedNADP.LightenergyfromPS1exciteselectronstoanevenhigherenergy

level.TheelectronsarethentranferredtoNADPalongwithaproton(Hion)toformreducedNADP.

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Light Dependent Reaction: CyclicPhotophosphorylation

ONLY PRODUCES ATP + ONLY USES PHOTOSYSTEM 1 (PS1)

Electrons from chlorophyll molecules aren't passed onto NADP, but are passed back to PS1 via

electron carriers. So electrons are recycled and repeatedly flow through PS1.

Electrons are excited by 700nm light energy absorbed by PS1, the excited electrons are sent to the

electron transport chain, as they travel down the ETC the electrons lose energy. This lost energy is

used to transport protons into the thylakoid, forming a proton gradient across the membrane. The

energy from this movement of phosphates causes ATP synthase to resynthesis ADP back to ATP.

However PS1 only produces a small amount of ATP.

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CALVINCYCLE-Stages

Stage1:CarbonFixation

Co2combineswithRuBPtoformanunstable6Carbonmolecule,whichimmediatelybreaksdown

into2moleculesofglycerate3-phosphate(GP).CombinationofCo2andRuBPiscatalysedby

RUBISCO(ribulosebiphosphatecarboxylase).

Stage2:ATPandNADPreduceGPtoatriosephosphate.

ATPusesenergytoreduceGPtotriosephosphate(TP).Thereactionalsorequiresreduced

NADP,whichaddsaHiontotheTP.TheNADPisthenrecycled.TheTPisconvertedintoglucose

andotherusefulorganiccompounds.

Stage3:Regeneration

RegeneratingRuBPrequiresmoreenergyviaATP.5outofevery6moleculesofTParentused

tomakehexosesugarsbutareusedtoregenerateRuBP.

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Light Independent Reaction: CALVIN CYCLE

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CALVINCYCLE

Needstoturn6timesinordertomakeoneglucosemolecule.3turnsofthecalvincylceproduces

6TPmolecules(2TPformedforevery1Co2).However5/6oftheTPmoleculesareusedinregenerationofRuBP.

Soforevery3turnsofthecalvincycle,onlyonemoleculeofTPisproducedtomakeglucosewith.

Glucosehoweverneeds6C,so2TPmoleculesareneeded,meaningthecalvincyclehastoturn

6timestoproduceoneglucosemolecule,

6turnsofthecalvincyclerequires;18ATPand12reducedNADPmolecules.