Click here to load reader

Photosynthesis and Cellular Respiration

  • View

  • Download

Embed Size (px)


Photosynthesis and Cellular Respiration. Outline. I. Photosynthesis A. Introduction B. Reactions II. Cellular Respiration A. Introduction B. Reactions. Photosynthesis. Method of converting sun energy into chemical energy usable by cells - PowerPoint PPT Presentation

Text of Photosynthesis and Cellular Respiration

  • Photosynthesis and Cellular Respiration

  • OutlineI. PhotosynthesisA. IntroductionB. ReactionsII. Cellular RespirationA. IntroductionB. Reactions

  • PhotosynthesisMethod of converting sun energy into chemical energy usable by cellsAutotrophs: self feeders, organisms capable of making their own foodPhotoautotrophs: use sun energy e.g. plants photosynthesis-makes organic compounds (glucose) from lightChemoautotrophs: use chemical energy e.g. bacteria that use sulfide or methane chemosynthesis-makes organic compounds from chemical energy contained in sulfide or methane

  • PhotosynthesisPhotosynthesis takes place in specialized structures inside plant cells called chloroplastsLight absorbing pigment molecules e.g. chlorophyll

  • Overall Reaction6CO2 + 12 H2O + light energy C6H12O6 + 6O2+ 6H2OCarbohydrate made is glucoseWater appears on both sides because 12 H2O molecules are required and 6 new H2O molecules are madeWater is split as a source of electrons from hydrogen atoms releasing O2 as a byproductElectrons increase potential energy when moved from water to sugar therefore energy is required

  • Light-dependent ReactionsOverview: light energy is absorbed by chlorophyll molecules-this light energy excites electrons and boosts them to higher energy levels. They are trapped by electron acceptor molecules that are poised at the start of a neighboring transport system. The electrons fall to a lower energy state, releasing energy that is harnessed to make ATP

  • Energy ShuttlingRecall ATP: cellular energy-nucleotide based molecule with 3 phosphate groups bonded to it, when removing the third phosphate group, lots of energy liberated= superb molecule for shuttling energy around within cells.Other energy shuttles-coenzymes (nucleotide based molecules): move electrons and protons around within the cellNADP+, NADPH NAD+, NADP FAD, FADH2

  • Light-dependent ReactionsPhotosystem: light capturing unit, contains chlorophyll, the light capturing pigmentElectron transport system: sequence of electron carrier molecules that shuttle electrons, energy released to make ATPElectrons in chlorophyll must be replaced so that cycle may continue-these electrons come from water molecules, Oxygen is liberated from the light reactionsLight reactions yield ATP and NADPH used to fuel the reactions of the Calvin cycle (light independent or dark reactions)

  • Calvin Cycle (light independent or dark reactions)ATP and NADPH generated in light reactions used to fuel the reactions which take CO2 and break it apart, then reassemble the carbons into glucose.Called carbon fixation: taking carbon from an inorganic molecule (atmospheric CO2) and making an organic molecule out of it (glucose)Simplified version of how carbon and energy enter the food chain

  • Harvesting Chemical EnergySo we see how energy enters food chains (via autotrophs) we can look at how organisms use that energy to fuel their bodies.Plants and animals both use products of photosynthesis (glucose) for metabolic fuelHeterotrophs: must take in energy from outside sources, cannot make their own e.g. animalsWhen we take in glucose (or other carbs), proteins, and fats-these foods dont come to us the way our cells can use them

  • Cellular Respiration OverviewTransformation of chemical energy in food into chemical energy cells can use: ATPThese reactions proceed the same way in plants and animals. Process is called cellular respirationOverall Reaction:C6H12O6 + 6O2 6CO2 + 6H2O

  • Cellular Respiration OverviewBreakdown of glucose begins in the cytoplasm: the liquid matrix inside the cellAt this point life diverges into two forms and two pathwaysAnaerobic cellular respiration (aka fermentation)Aerobic cellular respiration

  • C.R. ReactionsGlycolysisSeries of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvateProcess is an ancient one-all organisms from simple bacteria to humans perform it the same wayYields 2 ATP molecules for every one glucose molecule broken downYields 2 NADH per glucose molecule

  • Anaerobic Cellular RespirationSome organisms thrive in environments with little or no oxygenMarshes, bogs, gut of animals, sewage treatment pondsNo oxygen used= anaerobicResults in no more ATP, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis.End products such as ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)

  • Aerobic Cellular Respiration Oxygen required=aerobic2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria1. Krebs Cycle2. Electron Transport Chain

  • Krebs CycleCompletes the breakdown of glucoseTakes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2OHydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2Production of only 2 more ATP but loads up the coenzymes with H+ and electrons which move to the 3rd stage

  • Electron Transport ChainElectron carriers loaded with electrons and protons from the Krebs cycle move to this chain-like a series of steps (staircase).As electrons drop down stairs, energy released to form a total of 32 ATPOxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water

  • Energy Tally36 ATP for aerobic vs. 2 ATP for anaerobic

    Glycolysis 2 ATP

    Krebs 2 ATP

    Electron Transport32 ATP 36 ATPAnaerobic organisms cant be too energetic but are important for global recycling of carbon