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Cellular Respiration
Cellular Respiration—the process by which cells break down food
molecules to produce ATP under aerobic conditions.
3 stages of cellular respiration
 glycolysis
 citric acid cycle (a.k.a. Krebs cycle  Hans Krebs)
 electron transport chain
Glycolysis—an anaerobic process (does not use oxygen).
 Occurs in the cytoplasm
 Glucose is broken down into 3-carbon molecules called
pyruvic acid.
 Produces only 2 ATP net. (4 are made but two are used up.)
Krebs cycle—an aerobic process (requires oxygen).
 Occurs in mitochondria
 Pyruvic acid is broken down and combined with other
molecules.
 Carbon dioxide (CO2) is released.
 Produces only 2 ATP, plus NADH and FADH2 (other energy
containing molecules.)
Electron transport chain—an aerobic process
 Occurs in mitochondria (*cell membrane in prokaryotes)
 NADH and FADH2 from the Krebs cycle go through a “chain”
of reactions and combine hydrogen and oxygen to form water
(H2O).
 Produces 32 ATP.
Fermentation—a process that can produce 2 ATP under
anaerobic conditions (without oxygen.)
In animal muscles, fermentation makes lactic acid.
In some simple organisms (like yeast and bacteria), fermentation
makes CO2 and alcohol.