Photosynthesis Study Notes

Light Reactions

  • Major Players in Light Reactions:

    • Reaction Center: Contains special chlorophyll a molecules (P680 in PS II, P700 in PS I) that absorb light energy and transfer excited electrons.

    • Photolysis: The process of splitting water molecules to release electrons, protons (H+), and molecular oxygen (O₂), providing electrons for the electron transport chain in Photosystem II. (2H<em>2O→4H++4e−+O</em>2)(2H<em>2O → 4H^+ + 4e^- + O</em>2)

    • Photosystems I and II: Complexes of pigments (chlorophylls and carotenoids) and proteins that capture light energy. Photosystem II (PS II) and Photosystem I (PS I) work in series in noncyclic photophosphorylation.

    • Redox-Driven Proton Pump (Cytochrome b6f Complex): A protein complex that uses the energy from electron transfer to pump protons from the stroma into the thylakoid space, establishing an electrochemical gradient.

    • Cytochrome b6f Complex: Facilitates the transfer of electrons from PS II to PS I and actively pumps protons across the thylakoid membrane.

    • Electron Carriers:

      • Plastoquinone (Pq): A mobile electron carrier that transports electrons from PS II to the Cytochrome b6f complex.

      • Plastocyanin (Pc): A small, water-soluble protein that carries electrons from the Cytochrome b6f complex to PS I.

      • Ferredoxin (Fd): An iron-sulfur protein that accepts electrons from PS I and transfers them to the enzyme Ferredoxin-NADP+ Reductase (FNR).

      • Ferredoxin NADP+ Reductase (FNR): An enzyme that catalyzes the reduction of NADP+ to NADPH using electrons from Ferredoxin and protons from the stroma. (NADP++2e−+H+→NADPH)(NADP^+ + 2e^- + H^+ \rightarrow NADPH)

    • ATP Synthase: An enzyme complex embedded in the thylakoid membrane that uses the energy from the proton gradient (proton-motive force) to synthesize ATP from ADP and inorganic phosphate (Pᵢ).

ATP Synthase

  • Structure and Function: Composed of two main parts: $F0$ (transmembrane channel for H+) and $F1$ (catalytic knob responsible for ATP synthesis).

  • F1 ATPase: The catalytic component of ATP synthase located in the stroma, responsible for the conversion of ADP and Pᵢ into ATP.

  • Mechanism: Protons flow through the $F0$ channel into the stroma, causing the $F1$ unit to rotate, which drives the conformational changes necessary for ATP synthesis.

  • Reactants and Products: (ADP+Pi→ATP)(ADP + P_i \rightarrow ATP) (Phosphorylation of ADP)

Mitochondrion and Chloroplast Structure

Mitochondrion

  • Structure: Key components involved in energy production through cellular respiration.

    • Inter-membrane Space: Region between the outer and inner membranes, where the proton gradient is established during oxidative phosphorylation.

    • Inner Membrane: Folded into cristae, housing the electron transport chain complexes and ATP synthase.

    • Electron Transport Chain: A series of protein complexes that transfer electrons, generating a proton gradient across the inner mitochondrial membrane.

    • Matrix: The innermost compartment where the Krebs cycle occurs, producing NADH and FADH2FADH_2 for the ETC.

Chloroplast

  • Structure: Components involved in photosynthesis.

    • Thylakoid Space (Lumen): The inner compartment of the thylakoid, where protons accumulate to form a gradient.

    • Thylakoid Membrane: The site of the light-dependent reactions, containing photosystems, electron carriers, and ATP synthase.

    • Stroma: The fluid-filled space surrounding the thylakoids, where the Calvin cycle (light-independent reactions) takes place.

    • ATP Synthase at Thylakoid Membrane: Located in the thylakoid membrane, it utilizes the proton gradient between the thylakoid space and the stroma to produce ATP.

  • H+ Diffusion: Mechanism to generate a proton gradient (proton-motive force) essential for ATP synthesis.

    • Higher [H+] in Thylakoid Space: Achieved by the splitting of water (photolysis) and the pumping of protons by the Cytochrome b6f complex.

    • Lower [H+] in Stroma: Due to the consumption of protons by NADP+ reductase and the flow of protons through ATP synthase.

Photosystem Mechanics

Photosystems Overview

  • Thylakoid Membrane: The site where light energy is absorbed by pigment molecules within photosystems.

  • Photosystem (PS): A complex consisting of:

    • Light-harvesting complex (Antenna complex): Contains various pigment molecules (chlorophyll a, chlorophyll b, carotenoids) that absorb light energy and transfer it to the reaction center.

    • Primary electron transfer complex (Reaction center): Contains a special pair of chlorophyll a molecules that absorb energy and become excited, donating an electron to a primary electron acceptor.

  • Reaction: When the special pair of chlorophyll a molecules (P680 or P700) absorbs sufficient light energy, one of its electrons is boosted to a higher energy level and transferred to a primary electron acceptor.

Photosystem II (PS II)

  • Located in the thylakoid membrane.

  • Primary Acceptor: P680 (a pair of chlorophyll a molecules that absorbs light optimally at 680 nm).

  • Process: Light energy excites P680, causing it to donate an electron to the primary electron acceptor. P680 becomes P680+P680^+ (a very strong oxidizing agent).

  • Input: 2 H₂O + Photon → 1 O₂ + 4 H+ + 4 e-.

    • P680+P680^+ draws electrons from water molecules in the thylakoid lumen through photolysis, which also releases O₂ as a byproduct and adds H+ to the thylakoid space.

    • The excited electrons are then passed from the primary acceptor to Plastoquinone (Pq).

  • Product: Initiates the electron flow that ultimately contributes to ATP production and oxygen release.

Photosystem I (PS I)

  • Located mainly in the thylakoid membrane, particularly in unstacked regions.

  • Primary Acceptor: P700 (a pair of chlorophyll a molecules that absorbs light optimally at 700 nm).

  • Process: Receives electrons from the Cytochrome b6f complex (via Plastocyanin) to replace its own electrons lost upon light excitation.

    • Light energy excites P700, causing it to donate an electron to a primary electron acceptor, becoming P700+P700^+.

    • P700+P700^+ accepts electrons from Plastocyanin, which has carried them from the Cytochrome b6f complex.

    • These excited electrons are then passed to Ferredoxin (Fd) and ultimately assist in reducing NADP+ to NADPH by the enzyme Ferredoxin-NADP+ Reductase (FNR) in the stroma.

Electron Transport Chain and ATP Synthesis

  • Electron Flow: Involves a sequential transfer of electrons from PS II to PS I through various carriers and complexes.

    1. PS II donates electrons (derived from water splitting).

    2. Plastoquinone (Pq) accepts electrons from PS II.

    3. Cytochrome b6f complex: Accepts electrons from Pq, uses some of the electron energy to pump protons from the stroma into the thylakoid space, and then passes electrons to Plastocyanin.

    4. Plastocyanin (Pc): Carries electrons to PS I.

    5. PS I accepts electrons from Pc, re-energizes them with light, and passes them to Ferredoxin.

    6. Ferredoxin (Fd): Transfers electrons to Ferredoxin-NADP+ Reductase (FNR).

    7. FNR: Reduces NADP+ to NADPH in the stroma.

  • Proton Gradient Generation (Chemiosmosis): The pumping of H+ into the thylakoid space by the Cytochrome b6f complex and the release of H+ from water splitting create a high concentration of protons in the thylakoid lumen. Simultaneously, H+ are consumed in the stroma for NADPH synthesis, further steepening the gradient.

  • ATP Synthesis: The electrochemical potential energy stored in this proton gradient (the proton-motive force) drives the synthesis of ATP. H+ ions diffuse back out of the thylakoid space into the stroma through ATP synthase, rotating its $F_1$ subunit and catalyzing the phosphorylation of ADP to ATP.

Photophosphorylation Types

Noncyclic Photophosphorylation

  • Involves both Photosystems II and I: Electrons flow in a linear path from water to NADPH. This is the primary pathway for generating both ATP and NADPH required for the Calvin cycle.

  • Process: Light excites PS II (P680), electrons are extracted from water (H<em>2OH<em>2O), generating O</em>2O</em>2 and H+.Theseelectronsmovethroughtheelectrontransportchain(Pq,Cytochromeb6f,Pc)toPSI.LightexcitesPSI(P700),anditselectronsarepassedtoFerredoxinandthentoNADP+Reductase,reducingNADP+toNADPH.</p></li><li><p><strong>Products</strong>:GeneratesbothATPandNADPHinroughlyequalamounts,essentialfortheCalvincycle.AlsoproducesH+. These electrons move through the electron transport chain (Pq, Cytochrome b6f, Pc) to PS I. Light excites PS I (P700), and its electrons are passed to Ferredoxin and then to NADP+ Reductase, reducing NADP+ to NADPH.</p></li><li><p><strong>Products</strong>: Generates both ATP and NADPH in roughly equal amounts, essential for the Calvin cycle. Also producesO_2asabyproduct.</p></li></ul><h5id="f39538db−b028−414e−957d−0d7ff205cd22"data−toc−id="f39538db−b028−414e−957d−0d7ff205cd22"collapsed="false"seolevelmigrated="true">CyclicPhotophosphorylation</h5><ul><li><p><strong>InvolvesonlyPhotosystemI</strong>:ElectronsarerecycledbacktotheCytochromeb6fcomplexfromFerredoxininsteadofbeingpassedtoNADP+Reductase.</p></li><li><p><strong>Process</strong>:LightexcitesPSI(P700),electronsaretransferredtoFerredoxin.InsteadofgoingtoNADP+Reductase,FerredoxinpassestheelectronsbacktotheCytochromeb6fcomplex.TheCytochromeb6fcomplexthentransferselectronstoPlastocyanin,whichreturnsthemtoPSI.Thiselectronflowstillpumpsprotonsacrossthethylakoidmembrane.</p></li><li><p><strong>Function</strong>:ProducesadditionalATPwithoutgeneratingNADPHoras a byproduct.</p></li></ul><h5 id="f39538db-b028-414e-957d-0d7ff205cd22" data-toc-id="f39538db-b028-414e-957d-0d7ff205cd22" collapsed="false" seolevelmigrated="true">Cyclic Photophosphorylation</h5><ul><li><p><strong>Involves only Photosystem I</strong>: Electrons are recycled back to the Cytochrome b6f complex from Ferredoxin instead of being passed to NADP+ Reductase.</p></li><li><p><strong>Process</strong>: Light excites PS I (P700), electrons are transferred to Ferredoxin. Instead of going to NADP+ Reductase, Ferredoxin passes the electrons back to the Cytochrome b6f complex. The Cytochrome b6f complex then transfers electrons to Plastocyanin, which returns them to PS I. This electron flow still pumps protons across the thylakoid membrane.</p></li><li><p><strong>Function</strong>: Produces additional ATP without generating NADPH orO_2.ItisutilizedwhenthecellneedsmoreATPthanNADPH(e.g.,whenATPisbeingconsumedfasterthanNADPH,orwhenNADP+levelsarelow).</p></li></ul><h4id="344fcf86−dfc2−441b−80f6−6fc283328009"data−toc−id="344fcf86−dfc2−441b−80f6−6fc283328009"collapsed="false"seolevelmigrated="true">CalvinCycleOverview</h4><ul><li><p><strong>Location</strong>:Occursinthestromaofthechloroplast.</p></li><li><p><strong>ReactiveProcesses</strong>:UtilizestheATPandNADPHproducedduringthelightreactionstofixatmosphericCO2andconvertitintosugars,specificallyglyceraldehyde−3−phosphate(G3P).</p></li><li><p><strong>Phases</strong>:</p><ol><li><p><strong>CarbonFixation</strong>:</p><ul><li><p>TheenzymeRuBisCO(ribulose−1,5−bisphosphatecarboxylase/oxygenase)catalyzestheattachmentofoneCO2moleculetoafive−carbonsugar,ribulose−1,5−bisphosphate(RuBP).</p></li><li><p>Thisunstablesix−carbonintermediateimmediatelysplitsintotwomoleculesof3−phosphoglycerate(3−PGA),athree−carboncompound.</p></li><li><p><strong>Rubisco</strong>:ThemostabundantenzymeonEarth;actsasacarboxylase(fixingCO2)oranoxygenase(initiatingphotorespiration).</p></li></ul></li><li><p><strong>Reduction</strong>:</p><ul><li><p>Eachmoleculeof3−PGAreceivesanadditionalphosphategroupfromATP(using6ATPforevery3. It is utilized when the cell needs more ATP than NADPH (e.g., when ATP is being consumed faster than NADPH, or when NADP+ levels are low).</p></li></ul><h4 id="344fcf86-dfc2-441b-80f6-6fc283328009" data-toc-id="344fcf86-dfc2-441b-80f6-6fc283328009" collapsed="false" seolevelmigrated="true">Calvin Cycle Overview</h4><ul><li><p><strong>Location</strong>: Occurs in the stroma of the chloroplast.</p></li><li><p><strong>Reactive Processes</strong>: Utilizes the ATP and NADPH produced during the light reactions to fix atmospheric CO₂ and convert it into sugars, specifically glyceraldehyde-3-phosphate (G3P).</p></li><li><p><strong>Phases</strong>:</p><ol><li><p><strong>Carbon Fixation</strong>:</p><ul><li><p>The enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the attachment of one CO₂ molecule to a five-carbon sugar, ribulose-1,5-bisphosphate (RuBP).</p></li><li><p>This unstable six-carbon intermediate immediately splits into two molecules of 3-phosphoglycerate (3-PGA), a three-carbon compound.</p></li><li><p><strong>Rubisco</strong>: The most abundant enzyme on Earth; acts as a carboxylase (fixing CO₂) or an oxygenase (initiating photorespiration).</p></li></ul></li><li><p><strong>Reduction</strong>:</p><ul><li><p>Each molecule of 3-PGA receives an additional phosphate group from ATP (using 6 ATP for every 3CO_2fixed),becoming1,3−bisphosphoglycerate.</p></li><li><p>Then,1,3−bisphosphoglycerateisreducedbyNADPH(using6NADPHforevery3fixed), becoming 1,3-bisphosphoglycerate.</p></li><li><p>Then, 1,3-bisphosphoglycerate is reduced by NADPH (using 6 NADPH for every 3CO_2fixed)toformglyceraldehyde−3−phosphate(G3P).</p></li><li><p>G3PistheactualsugarproductoftheCalvincycle.ForeverysixG3Pmoleculesproduced,oneexitsthecycletobeusedbytheplant(e.g.,tosynthesizeglucose,sucrose,starch,orotherorganiccompounds),whiletheotherfiveremaininthecycle.</p></li></ul></li><li><p><strong>Regeneration</strong>:</p><ul><li><p>TheremainingfiveG3PmoleculesarerearrangedthroughaseriesofcomplexreactionstoregeneratethreemoleculesofRuBP.</p></li><li><p>ThisregenerationprocessrequiresthehydrolysisofATP(using3ATPforevery3fixed) to form glyceraldehyde-3-phosphate (G3P).</p></li><li><p>G3P is the actual sugar product of the Calvin cycle. For every six G3P molecules produced, one exits the cycle to be used by the plant (e.g., to synthesize glucose, sucrose, starch, or other organic compounds), while the other five remain in the cycle.</p></li></ul></li><li><p><strong>Regeneration</strong>:</p><ul><li><p>The remaining five G3P molecules are rearranged through a series of complex reactions to regenerate three molecules of RuBP.</p></li><li><p>This regeneration process requires the hydrolysis of ATP (using 3 ATP for every 3CO_2fixed)toensurethecyclecancontinuebyreplenishingthestartingmaterial,RuBP.</p></li></ul></li></ol></li></ul><h4id="0adcca86−5d84−4832−b12b−19393f8547c2"data−toc−id="0adcca86−5d84−4832−b12b−19393f8547c2"collapsed="false"seolevelmigrated="true">Photorespiration</h4><ul><li><p><strong>Mechanism</strong>:OccurswhenRuBisCObindswithfixed) to ensure the cycle can continue by replenishing the starting material, RuBP.</p></li></ul></li></ol></li></ul><h4 id="0adcca86-5d84-4832-b12b-19393f8547c2" data-toc-id="0adcca86-5d84-4832-b12b-19393f8547c2" collapsed="false" seolevelmigrated="true">Photorespiration</h4><ul><li><p><strong>Mechanism</strong>: Occurs when RuBisCO binds withO2insteadofinstead ofCO2.</p><ul><li><p>Underconditionsofhigh.</p><ul><li><p>Under conditions of highO2concentration(e.g.,hightemperaturesorwhenstomataclosetoconservewater,causingconcentration (e.g., high temperatures or when stomata close to conserve water, causingCO2levelstodropandlevels to drop andO_2levelstoriseinsidetheleaf),Rubisco’soxygenaseactivityincreases.</p></li><li><p>WhenRuBisCOreactswithlevels to rise inside the leaf), Rubisco’s oxygenase activity increases.</p></li><li><p>When RuBisCO reacts withO_2,itproducesonemoleculeof3−phosphoglycerate(3−PGA)andonemoleculeof2−phosphoglycolate(atwo−carboncompound),insteadoftwo3−PGAs.</p></li></ul></li><li><p><strong>Consequences</strong>:2−phosphoglycolatecannotbedirectlyusedintheCalvincycleandmustbeprocessed,consumingATPandreleasing, it produces one molecule of 3-phosphoglycerate (3-PGA) and one molecule of 2-phosphoglycolate (a two-carbon compound), instead of two 3-PGAs.</p></li></ul></li><li><p><strong>Consequences</strong>: 2-phosphoglycolate cannot be directly used in the Calvin cycle and must be processed, consuming ATP and releasingCO_2withoutproducingsugar.</p></li><li><p><strong>Impact</strong>:Reducestheefficiencyofphotosynthesisbydivertingresources,leadingtoasignificantlossoffixedcarbonandenergy.Enhancesstressonplantsinadverseconditions,drivingadaptationslikeC4andCAMpathways.</p></li></ul><h4id="068df398−fd1c−4e1c−96bf−3d09e0242f46"data−toc−id="068df398−fd1c−4e1c−96bf−3d09e0242f46"collapsed="false"seolevelmigrated="true">C4andCAMPathways</h4><h5id="fbd7109d−358c−47f5−9439−2f26f3d97c3a"data−toc−id="fbd7109d−358c−47f5−9439−2f26f3d97c3a"collapsed="false"seolevelmigrated="true">AdvantagesofC4Plants</h5><ul><li><p><strong>Examples</strong>:Corn,sugarcane,tropicalgrasses.</p></li><li><p><strong>Mechanism</strong>:Utilizeaspecializedenzyme,PEPcarboxylase,forinitialcarbonfixation,whichhasamuchhigheraffinityforwithout producing sugar.</p></li><li><p><strong>Impact</strong>: Reduces the efficiency of photosynthesis by diverting resources, leading to a significant loss of fixed carbon and energy. Enhances stress on plants in adverse conditions, driving adaptations like C4 and CAM pathways.</p></li></ul><h4 id="068df398-fd1c-4e1c-96bf-3d09e0242f46" data-toc-id="068df398-fd1c-4e1c-96bf-3d09e0242f46" collapsed="false" seolevelmigrated="true">C4 and CAM Pathways</h4><h5 id="fbd7109d-358c-47f5-9439-2f26f3d97c3a" data-toc-id="fbd7109d-358c-47f5-9439-2f26f3d97c3a" collapsed="false" seolevelmigrated="true">Advantages of C4 Plants</h5><ul><li><p><strong>Examples</strong>: Corn, sugarcane, tropical grasses.</p></li><li><p><strong>Mechanism</strong>: Utilize a specialized enzyme, PEP carboxylase, for initial carbon fixation, which has a much higher affinity forCO2thanRubiscoanddoesnotbindthan Rubisco and does not bindO2.</p></li><li><p><strong>SpatialSeparation</strong>:TheplantspatiallyseparatesCO2fixationfromtheCalvincycle.</p><ol><li><p>.</p></li><li><p><strong>Spatial Separation</strong>: The plant spatially separates CO₂ fixation from the Calvin cycle.</p><ol><li><p>CO_2isfirstfixedbyPEPcarboxylaseinmesophyllcells,formingafour−carboncompound(oxaloacetate,whichisconvertedtomalate).</p></li><li><p>Thismalateisthentransportedtospecializedbundlesheathcells,whicharetightlypackedaroundthevascularbundles.</p></li><li><p>Inthebundlesheathcells,malatereleasesis first fixed by PEP carboxylase in mesophyll cells, forming a four-carbon compound (oxaloacetate, which is converted to malate).</p></li><li><p>This malate is then transported to specialized bundle sheath cells, which are tightly packed around the vascular bundles.</p></li><li><p>In the bundle sheath cells, malate releasesCO2,creatingahigh, creating a highCO2concentration(concentration (CO_2pump)forRubiscotooperateefficientlyintheCalvincycle,minimizingphotorespirationevenwhenstomataarepartiallyclosed.</p></li></ol></li><li><p><strong>Adaptation</strong>:Highlyefficientinhot,dry,andhigh−lightenvironments.</p></li></ul><h5id="c9d1b1f0−6a96−41de−b072−46db151bb27f"data−toc−id="c9d1b1f0−6a96−41de−b072−46db151bb27f"collapsed="false"seolevelmigrated="true">AdvantagesofCAMPlants</h5><ul><li><p><strong>Examples</strong>:Cacti,pineapples,succulents.</p></li><li><p><strong>Mechanism</strong>:Utilizecrassulaceanacidmetabolism(CAM).</p></li><li><p><strong>TemporalSeparation</strong>:TheplanttemporallyseparatesCO2fixationfromtheCalvincycle.</p><ol><li><p><strong>Night</strong>:Stomataareopen,andpump) for Rubisco to operate efficiently in the Calvin cycle, minimizing photorespiration even when stomata are partially closed.</p></li></ol></li><li><p><strong>Adaptation</strong>: Highly efficient in hot, dry, and high-light environments.</p></li></ul><h5 id="c9d1b1f0-6a96-41de-b072-46db151bb27f" data-toc-id="c9d1b1f0-6a96-41de-b072-46db151bb27f" collapsed="false" seolevelmigrated="true">Advantages of CAM Plants</h5><ul><li><p><strong>Examples</strong>: Cacti, pineapples, succulents.</p></li><li><p><strong>Mechanism</strong>: Utilize crassulacean acid metabolism (CAM).</p></li><li><p><strong>Temporal Separation</strong>: The plant temporally separates CO₂ fixation from the Calvin cycle.</p><ol><li><p><strong>Night</strong>: Stomata are open, andCO_2istakeninandfixedbyPEPcarboxylase,formingfour−carbonacids(likemalate),whicharestoredinthecell′svacuoles.</p></li><li><p><strong>Day</strong>:Stomataareclosedtoconservewater.Thestoredmalateisreleasedfromthevacuolesandbrokendowntoreleaseis taken in and fixed by PEP carboxylase, forming four-carbon acids (like malate), which are stored in the cell's vacuoles.</p></li><li><p><strong>Day</strong>: Stomata are closed to conserve water. The stored malate is released from the vacuoles and broken down to releaseCO2.This. ThisCO2thenenterstheCalvincycle,whichiscarriedoutbyRubiscointhesamecells.</p></li></ol></li><li><p><strong>Adaptation</strong>:Extremelywell−adaptedtoaridenvironments,allowingthemtominimizewaterlossbykeepingstomataclosedduringtheday.</p></li></ul><h4id="35b1073c−027c−4ab2−acaa−53894a55c9c5"data−toc−id="35b1073c−027c−4ab2−acaa−53894a55c9c5"collapsed="false"seolevelmigrated="true">SummaryofPhotosynthesis</h4><h5id="97643901−df12−42e8−b688−1ff8d19aa963"data−toc−id="97643901−df12−42e8−b688−1ff8d19aa963"collapsed="false"seolevelmigrated="true">LightReactionsSummary</h5><ul><li><p><strong>Location</strong>:Thylakoidmembranes.</p></li><li><p><strong>Process</strong>:ConvertlightenergyintochemicalenergyintheformofATPandNADPH.</p></li><li><p><strong>Inputs</strong>:Lightenergy,then enters the Calvin cycle, which is carried out by Rubisco in the same cells.</p></li></ol></li><li><p><strong>Adaptation</strong>: Extremely well-adapted to arid environments, allowing them to minimize water loss by keeping stomata closed during the day.</p></li></ul><h4 id="35b1073c-027c-4ab2-acaa-53894a55c9c5" data-toc-id="35b1073c-027c-4ab2-acaa-53894a55c9c5" collapsed="false" seolevelmigrated="true">Summary of Photosynthesis</h4><h5 id="97643901-df12-42e8-b688-1ff8d19aa963" data-toc-id="97643901-df12-42e8-b688-1ff8d19aa963" collapsed="false" seolevelmigrated="true">Light Reactions Summary</h5><ul><li><p><strong>Location</strong>: Thylakoid membranes.</p></li><li><p><strong>Process</strong>: Convert light energy into chemical energy in the form of ATP and NADPH.</p></li><li><p><strong>Inputs</strong>: Light energy,H_2O,ADP,NADP+.</p></li><li><p><strong>Outputs</strong>:ATP,NADPH,and, ADP, NADP+.</p></li><li><p><strong>Outputs</strong>: ATP, NADPH, andO_2(asabyproductfromsplittingwatermolecules).</p></li></ul><h5id="3693738a−44fe−4c20−ad60−be5c8adcb68d"data−toc−id="3693738a−44fe−4c20−ad60−be5c8adcb68d"collapsed="false"seolevelmigrated="true">CalvinCycleSummary</h5><ul><li><p><strong>Location</strong>:Stromaofthechloroplast.</p></li><li><p><strong>Process</strong>:UtilizesthechemicalenergyfromATPandthereducingpowerfromNADPHtofixatmospheric(as a byproduct from splitting water molecules).</p></li></ul><h5 id="3693738a-44fe-4c20-ad60-be5c8adcb68d" data-toc-id="3693738a-44fe-4c20-ad60-be5c8adcb68d" collapsed="false" seolevelmigrated="true">Calvin Cycle Summary</h5><ul><li><p><strong>Location</strong>: Stroma of the chloroplast.</p></li><li><p><strong>Process</strong>: Utilizes the chemical energy from ATP and the reducing power from NADPH to fix atmosphericCO_2intoorganicsugar(G3P).</p></li><li><p><strong>Inputs</strong>:into organic sugar (G3P).</p></li><li><p><strong>Inputs</strong>:CO_2$$, ATP, NADPH.

  • Outputs: G3P (sugar) for plant growth and other metabolic processes, and regenerates ADP, inorganic phosphate (Pᵢ), and NADP+ for reuse in the light reactions.