Cellular Respiration In photosynthesis, light energy is stored in the bonds of glucose molecules in the chloroplasts of plant cells (or other autotrophs).

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  • Cellular RespirationIn photosynthesis, light energy is stored in the bonds of glucose molecules in the chloroplasts of plant cells (or other autotrophs).In respiration, energy is released from the glucose molecules so the cells of organisms can use it for basic cell functions.

  • Compare:

    CO2 + H2O --- light energy -- C6H12O6 + O2

    C6H12O6 + O2 ---- CO2 + H2O + energy

    (3811 calories of energy to be exact)

  • The breakdown of glucose:

    I GlycolysisTakes place in the cytoplasmGlucose is broken in half forming two 3 carbon moleculesof pyruvic acidRequires 2 ATP molecules to get the process startedProduces 4 ATP (net gain of 2 ATP)NAD+ accepts high energy electrons, forms NADHCells can produce thousands of ATP in millisecondsProcess does not require oxygen

  • After glycolysis, pyruvic acid can follow one of two paths:When oxygen is NOT present...Anaerobic pathways called fermentationEither alcoholic or lactic acid fermentationWhen oxygen IS presentAerobic pathway called cellular respirationConsists of the Krebs Cycle and Electron Transport chain

  • II Fermentation (anaerobic)Alcoholic fermentation:Yeastswine, beer, breadProduces ethyl alcohol and CO2 (waste products) + ATPfrom glycolysisRegenerates NAD+ so it can be used again in glycolysis

    Lactic acid fermentation:When the body cannot supply enough O2 for the aerobic pathwayburning sensation in musclesRegenerates NAD+ so it can be used again in glycolysisLactic acid (waste product) + ATP from glycolysisBacteria produce cheese, yogurt, sour cream, pickles,sauerkraut

  • III Cellular respiration (aerobic)

    Krebs Cycle (citric acid cycle)Pyruvic acid enters mitochondriaProduces CO2 as waste product1 molecule of ADP ATP4 NAD+ NADH1 FAD FADH2NADH and FADH2 carry high energy electrons

    Electron Transport ChainHigh energy electrons passed from carrier to carrierTheir energy is used to convert ADP to ATPOnce the electrons have lost most of their energy, theyare accepted by H+ and O2, forming water

  • Cellular Respiration (cont)

    From 1 glucose molecule:

    Glycolysis 2 ATP

    Krebs Cycle andElectron Transport 34 ATP

    Total for Cellular Respiration 36 ATP(compared to only 2 ATPin the anaerobic pathway)You recover 38 % of the energy in each glucose molecule.The rest is lost as heat energy.


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