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Photosynthesis and Cellular Respiration. Chapter 9. Energy in Living Systems. Section 1. Chemical Energy. Organisms use and store energy in chemical bonds of organic compounds Almost all energy in organic compounds comes from the sun - PowerPoint PPT Presentation

Text of Photosynthesis and Cellular Respiration

Photosynthesis and Cellular Respiration

Chapter 9Photosynthesis and Cellular RespirationEnergy in Living SystemsSection 1Chemical EnergyOrganisms use and store energy in chemical bonds of organic compoundsAlmost all energy in organic compounds comes from the sunSolar energy enters living systems when plants, algae, and certain prokaryotes use sunlight to carry out photosynthesisChemical EnergyPhotosynthesis: the process by which sunlight, carbon dioxide, and water are used to produce carbohydrates and oxygenOrganisms that are able to perform photosynthesis are called autotrophsChemical EnergyIn order to survive, organisms that cannot make their own food must absorb food molecules made by autotrophs, eat autotrophs, or eat organisms that consume autotrophsThese food molecules supply energy for the cellsEnergy is stored in molecular bondsMetabolism and the Carbon CycleMetabolism involves either using energy to build organic molecules or breaking down organic molecules in which energy is storedOrganic molecules contain carbonTherefore, an organisms metabolism is part of Earths carbon cycleMetabolism and the Carbon CyclePhotosynthesisEnergy enters an ecosystem when organisms use sunlight during photosynthesis to convert carbon dioxide into glucoseTakes place in the chloroplastsMetabolism and the Carbon CycleCellular RespirationOrganisms extract energy stored in glucose moleculesThrough cellular respiration, cells make the carbon in glucose into carbon dioxide molecules and produce energyMetabolism and the Carbon CycleCellular respirationInputs:GlucoseSix oxygen moleculesOutputs:Six carbon dioxide moleculesSix water moleculesEnergy (ATP, which is the main energy source for all cell processes)C6H12O6 + 6O2 6CO2 + 6 H2O + Energy

Transferring EnergyIn chemical reactions, energy can be absorbed and released during the breaking and forming of bondsIn cells, chemical energy is gradually released in a series of chemical reactions that are assisted by enzymesEnzymes: proteins that act as catalysts in reactionsTransferring EnergyATPWhen cells break down food molecules, some of the energy in the molecules is released as heatCells use much of the remaining energy to make ATPUsed to power chemical reactionsPortable form of energyCan be made in one place and used in anotherNucleotide made up of a chain of three phosphate groupsTransferring EnergyATP SynthaseAn enzyme that catalyzes the synthesis of ATPATP synthase recycles ADP by bonding a third phosphate group to the moleculeActs as a carrier protein and an enzyme for hydrogen ions

ATP Synthase

Transferring EnergyHydrogen Ion PumpElectron transport chain: a series of molecules is the inner membrane of a mitochondrionAllows electrons to drop in energy as they are passed along and uses the energy released to pump H+ ions out of a mitochondrions inner compartmentElectron Transport Chain

PhotosynthesisSection 2IntroductionPlants, algae, and certain prokaryotes capture about 1% of the energy in the sunlight that reaches Earth and convert it to chemical energy through photosynthesisPhotosynthesis provides energy from almost all lifeHarvesting Light EnergyThe cells of many photosynthetic organisms have chloroplastsChloroplasts convert light energy into chemical energyHarvesting Light EnergyChloroplastsHave an outer membrane and an inner membraneInner membrane is highly selectiveBoth allow light to pass throughStroma: space inside the inner membraneInside the stroma are thylakoid membranesFolded to produce flat, disc-like sacs called thylakoidsThylakoids arranged in stacksPhotosynthesis starts when light hits these stacksThylakoids contain molecules that absorb light energy


Harvesting EnergyElectromagnetic radiationLight is a form of electromagnetic radiationA form of energy that can travel through empty space in the form of wavesDifferent wavelengths correspond to a certain amount of energySunlight contains all wavelengths of visible lightHarvesting EnergyPigments Pigment: a substance that absorbs certain wavelengths (colors) of light and commonly reflects all of the othersIn plants, light energy is harvested by pigments that are located in the thylakoid membrane of chloroplastsChlorophyll: a green pigment that absorbs light energy to start photosynthesisAbsorbs mostly red and blue light and reflects green and yellowHarvesting EnergyPigmentsPlants have two types of chlorophyll:Chlorophyll aChlorophyll bPlants also have carotenoidsReflect yellow, orange, and red lightWhy do leaves change color in the fall?Chlorophyll fades away, so the carotenoids are exposed

Harvesting Light EnergyElectron carriersWhen light hits a thylakoid, energy is absorbed by many pigment moleculesThey funnel the energy to the reaction center (a special chlorophyll molecule)Energy causes electrons to become excited and move to a higher energy level; they are transferred down the chain to an electron carrier

Two Electron Transport ChainsThe electron carrier transfers the electrons to the first of two electron transport chains in the thylakoid membraneDuring photosynthesis, one electron transport chain provides energy to make ATP, while the other provides energy to make NADPHTwo Electron Transport ChainsProducing ATPIn mitochondria, electron transport chains pump H+ ions through a membrane, which produces a concentration gradientAlso happens in chloroplastsTwo Electron Transport ChainsStep 1: Water SplittingStep 2: Hydrogen Ion PumpStep 3: ATP SynthaseStep 4: ReenergizingStep 5: Making NADPH

Two Electron Transport ChainsStep 1: Water SplittingExcited electrons that leave the chlorophyll have to be replaced by other electronsReplaced from H2OWater is split by an enzymeH+ ions and O2 molecules produced

Two Electron Transport ChainsStep 2: Hydrogen Ion PumpsProtein acts as a membrane pumpExcited electrons transfer some energy to pump H+ ions into the thylakoidCreates a concentration gradient

Two Electron Transport ChainsStep 3: ATP SynthaseThe energy from the diffusion of H+ ions through the carrier protein is used to make ATPAs hydrogen ions pass through the channel portion of the protein, ATP synthase catalyzes a reaction in which a phosphate group is added to a molecule of ADPResults in ATP

Two Electron Transport ChainsProducing NADPHWhile one electron transport chain provides energy to make ATP, a second electron transport chain receives excited electrons from a chlorophyll molecule and uses them to make NADPH

Two Electron Transport ChainsStep 4: ReenergizingIn this second chain, light excites electrons in the chlorophyll moleculeThe electrons are passed to the second electron transport chainTwo Electron Transport ChainsStep 5: Making NADPHExcited electrons combine with H+ ions and NADP+ (an electron acceptor) Both NADPH and the ATP made during the first stage of photosynthesis will be used to provide the energy to carry out the final stage of photosynthesis

Producing SugarThe first two stages of photosynthesis depend directly on light because light energy is used to make ATP and NADPHIn the first stage of photosynthesis, ATP and NADPH are used to produce energy-storing sugar molecules from the carbon in carbon dioxideThe use of carbon dioxide is called carbon fixingProducing SugarThe reactions that fix carbon dioxide are light-independent reactionsSometimes called dark reactionsSeveral ways in which carbon dioxide is fixedMost common method is the Calvin CycleProducing SugarCalvin CycleCarbon FixationIn CO2 fixation, an enzyme adds a molecule of CO2 to a 5-carbon compoundOccurs three times to yield three 6-carbon moleculesTransferring EnergyEach 6-carbon compound splits into two 3-carbon compoundsPhosphate groups from ATP and electrons from NADPH are added to the compounds to form higher energy 3-carbon compoundsProducing SugarMaking SugarOne of the 3-carbon sugars leaves the Calvin Cycle and is used to make organic compoundsRecyclingThe remaining five 3-carbon sugars are rearrangedUsing the energy from ATP, enzymes reform three molecules of the initial 5-carbon compoundCompletes the cycleCalvin Cycle

Factors that Affect PhotosynthesisLight intensity, carbon dioxide concentration, and temperature are three environmental factors that affect photosynthesisThe rate of photosynthesis increases and light intensity increases until all chlorophyll molecules are being used, which causes the process to level offThe concentration of CO2 affects the rate of photosynthesis in the same way as light intensityUnfavorable temperatures may inactivate certain enzymes so reactions dont take placeCellular RespirationSection 3GlycolysisThe primary fuel for cellular respiration is glucoseFormed when carbs are broken downProteins and nucleic acids can also be used to make ATPSteps of GlycolysisIn the first stage of cellular respiration, glucose is broken down in the cytoplasm by glycolysisGlycolysis: enzymes break down one 6-carbon molecule of glucose into two 3-carbon pyruvate moleculesSteps of GlycolysisBreaking Down GlucoseTwo ATP molecules are used to break glucose into two smaller unitsA phosphate group from ATP is added to the 6-carbon compoundbreaks into two 3-carbon sugarsSteps of GlycolysisNADH ProductionEach 3-carbon compound reacts with another phosphate group (not from ATP)Hydrogen atoms are transferred to two molecules of NAD+Produces two molecules of NADHSteps of GlycolysisPyruvate ProductionEach 3-carbon sugar is converted into a 3-cadrbon molecule of pyruvateProduces 4 ATP moleculesThe breaking of a sugar molecule by glycolysis results in a net gain of two ATP molecules


GlycolysisGlycolysis is the only source of energy for some prokaryotesGlycolysis is anaerobic (doesnt require oxygen)Aerobic: requires oxygenIn aerobic respiration, the pyruvate product of glycolysis undergoes another series of reactions to produce more ATP moleculesAerobic RespirationOrganisms can use oxygen to produce ATP efficiently through aerobic respirationPyruvate is broken down in the Krebs cycleKrebs cycle: a series of reactions that produce electron carriersElectron carriers enter an electron transport chain, which powers ATP synthaseUp to 34 ATP molecules can be produced from one glucose molecule in aerobic respirationKrebs CycleBegins with pyruvate (produced during glycolysis)Pyruvate releases a CO2 molecule to form a 2-carbon compoundAn enzyme attaches this 2-carbon compound to a 4-carbon compound and forms a 6-carbon compoundKrebs CycleThe 6-carbon compound releases 1 CO2 molecule, and then anotherEnergy is released, and forms NADHThe 4-carbon molecule is converted to the 4-carbon compound that began the cycleAnd the cycle starts over again

Krebs CycleProducts of the Krebs Cycle1 ATP3 NADH1 FADH2

Electron carriers transfer energy through the electron transport chain, which powers ATP synthaseKrebs Cycle

Electron Transport ChainSecond stage of aerobic respirationTakes place in the inner membranes of the mitochondriaElectron Transport ChainElectrons carried by NADH and FADH2 pass through the chainEnergy is transferredEnergy is used to transport hydrogen ions out of the inner mitochondrial compartmentConcentration gradient across the inner membrane is createdHydrogen ions diffuse through ATP synthaseEnergy is produced, which is used to make ATP from ADPOxygen combines with the electrons and two hydrogen ions to form two water moleculesEssential that oxygen is present!! If not, the chain stopsElectron Transport Chain

FermentationMany prokaryotes live entirely on the energy released in glycolysisGlycolysis produces two ATP molecules and one NADHNADH must be able to transfer its electrons so that NAD+ is continuously availableIf in anaerobic conditions, the electron transport chain wont workSo organisms need another way to make NAD+FermentationFermentation: the process of breaking down carbohydrates in the absence of oxygenRecycles NAD+ that is needed to keep making ATP through glycolysisTwo types:Lactic acid fermentationAlcoholic fermentationFermentationLactic Acid FermentationEnd products of glycolysis are three-carbon pyruvate moleculesPyruvate is converted into lactic acid through lactic acid fermentationOccurs in the muscles of animalsDuring heavy exercise, muscle cells must operate without oxygenGlycolysis becomes the only source of ATPNAD+ has to be recycled through lactic acid fermentation in order for glycolysis to continueFermentationLactic Acid fermentationDuring heavy exercise, muscle cells must operate without oxygenGlycolysis becomes the only source of ATPNAD+ has to be recycled through lactic acid fermentation in order for glycolysis to continue

FermentationAlcoholic FermentationAn enzyme removes CO2 from the three-carbon pyruvate to form a two-carbon moleculeThen, a second enzyme adds electrons and hydrogen from NADH to the molecule to form ethanol (ethyl alcohol)Called alcoholic fermentationNAD+ is recycled and glycolysis can continueFermentation

FermentationEfficiency of Cellular RespirationThe total amount of ATP that a cell can use from each glucose depends on whether oxygen is present or notGlycolysis: produces 2 ATPAnaerobic processes: recycles NAD+ to continue forming ATPAerobic processes: can produce up to 34 ATP moleculesFermentationEfficiency of Cellular RespirationCells are most efficient when oxygen is present because they make most of their ATP during aerobic respirationFor each molecule of glucose, two ATP can be producedCellular Respiration