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Overview of Cellular Respiration
Section 4.4
 Cellular respiration makes ATP by breaking
down sugars.
 If a step requires oxygen, it is called aerobic.
 If a step occurs in the absence of oxygen, it is
called anaerobic.
 It takes place in three steps:
 Glycolysis
 Krebs cycle
 Electron transport chain
Cellular respiration
 The equation for cellular respiration is:
C6H12O6 + 6 O2  6 H2O + 6 CO2 + energy
 The equation for photosynthesis is:
6 H2O + 6 CO2 + light energyC6H12O6 + 6 O2
Comparing photosynthesis with respiration
Glycolysis
 Is anaerobic
 Occurs in the cytoplasm
 One 6 carbon glucose molecule is broken down
into two three carbon pyruvate molecules.
 Produces 2 ATP molecules
Krebs Cycle
 Is aerobic
 Occurs in mitochondria
 Pyruvate is broken down
 One 2 carbon molecule
 1 CO2 molecule
 High energy electrons
 CoEnzyme A bonds to
the 2 carbon molecule
Krebs Cycle
 Acetyl CoA enters the Krebs cycle (2C)
 Combines with a 4 carbon
molecule to form
citric acid (6C)
 Loses a CO2 (5C)
 Loses another CO2 (4C)
 Combines with acetyl CoA.
 Produces 2 ATP
Electron Transport Chain
 Is aerobic
 Occurs in mitochondria
 NADH and FADH2 donate electrons and
transport hydrogen ions.
 Produces 34 ATP molecules
 Hydrogen ions and electrons combine with
oxygen to produce water.
Electron Transport Chain
Aerobic respiration
 Aerobic respiration can produce up to
38 ATP molecules from 1 molecule of
glucose.
 Most ATP is produced in the electron
transport chain.
Anaerobic Respiration
 Also called fermentation
 In the absence of oxygen
 If there is no oxygen to accept electrons or
hydrogen ions
 NADH and FADH2 cannot be converted to
NAD+ and FAD2+
 Citric acid is not broken down in the Krebs
cycle
 Acetyl CoA cannot enter the Krebs cycle
Anaerobic respiration
 Pyruvate has to be broken down another way.
 In yeasts:
 Pyruvate  ethanol and CO2
 Produces 2 ATP molecules
 In animals:
 Pyruvate  lactic acid
 Produces 2 ATP molecules
Uses of fermentation
 Cheese
 Alcohol
 Breads