Aerobic Respiration
 Only occur in the presence of oxygen
 Two stages
 Krebs Cycle
 Electron Transport Chain

with chemiosmosis
 Prokaryotes
 Occur in cytosol
 Eukaryotes
 Occur in mitochondria
Aerobic Respiration
 After glycolysis, pyruvic
acids are produced
 Pyruvic acid moves inside
mitochondria into
mitochondrial matrix (space
between two membranes)
 Pyruvic acid + CoA 
Acetyl CoA + CO2
The Krebs Cycle
 Acetyl CoA  CO2 + H + ATP
 The H produced reduce NAD+  NADH
 Five steps in the Krebs Cycle
 Occurs in mitochondrial matrix
 Citric Acid is made in Step 1 therefore this is also
called the Citric Acid cycle
 Net ATP produced is 2 ATP
Krebs Cycle - Step 1
 Acetyl CoA + oxaloacetic acid  Citric
Acid
 This step releases CoA back into the
mitochondrial matrix for pyruvic acid to be
fixed again
Krebs Cycle – Step 2
 Citric acid releases CO2 and H
 Becomes a 5-carbon compound
 The H released, reduces the NAD+ to NADH
Krebs Cycle – Step 3
 Five carbon compound releases another
CO2 and H
 Becomes a 4 carbon compound
 Another NAD+ is reduced to NADH
 Produces an ATP
Krebs Cycle – Step 4
 4 carbon compound releases H atom
 This time, FAD is reduced to FADH2
 Similar molecule to NAD+
Krebs Cycle – Step 5
 4 carbon compound releases H atom
 Reduces NAD+ to NADH
 This reaction regenerates initial oxaloacetic acid
Electron Transport Chain
 Uses the high-energy e- from the Krebs Cycle to
convert ADP to ATP
 Total net ATP produced is 34!!
 Prokaryotes
 Occurs on cell membrane of organism
 Eukaryotes
 Occurs in the mitochondria
membrane called cristae
ETC – Step 1
 NADH & FADH2 are used to power this chain
of reactions
 NADH & FADH2 are oxidized (lose e-) to the
electron transport chain
 Also donate H atoms
 NADH  NAD+
 FADH2  FAD+
ETC – Step 2
 Electrons from NADH & FADH2 are passed down
chain
 Lose some energy each time passed on
ETC – Step 3
 Lost energy from e- transferring down the chain
pump protons (H+)
 This creates high conc. of H+ between inner and
outer membranes
 Creates a concentration gradient & electrical
gradient since H+ are positive
ETC – Step 4
 Concentration & electrical gradient in membranes
produce ATP molecules by chemiosmosis
 ATP synthase is protein embedded in membrane
that pumps protons out and creates ATP
ETC – Step 5
 The electrons move to final acceptor down the
chain
 Oxygen is the final acceptor
 Oxygen also accepts protons provided by NADH &
FADH2
 The protons, electrons, and oxygen all combine to
produce H2O
Importance of Oxygen
 The only way to produce ATP is by the movement
of electrons in the ETC
 Oxygen is the final acceptor
 Without oxygen, the ETC would halt

Efficiency of Aerobic
Respiration
Glycolysis = 2 ATP
 Krebs Cycle = 2 ATP
 ETC = 34 ATP
 Total = 38 ATP!!
Efficiency Equation
 Depends on conditions of the cell
 How ATP are transported
 Cellular respiration is 20 times more efficient
than glycolysis
Summary
 Cellular respiration
 Glycolysis

Glucose  pyruvic acid + ATP + NADH
 Aerobic respiration

Pyruvic acid  CO2 + H2O + ATP
Energy & Exercise
 Quick energy – Lactic Acid fermentation is
used to get quick energy and gives off
lactic acid as a by product, thus the muscle
pain.
 Long-Term Energy – Use cellular respiration
to produce energy. Exercising or activities
that last for at least 15 to 20 minutes. Best
form for weight control.
Comparing Photosynthesis &
Respiration
Photosynthesis
Cellular
Respiration
Function
Energy Storage
Location
Chloroplasts
Energy
Release
Mitochondria
Reactants
CO2 and H2O
Products
C6H12O6 and O2
C6H12O6 and
O2
CO2 and H2O
Equation
6CO2 + 6H2O 
C6H12O6 + 6O2
C6H12O6 + 6O2
6CO2 + 6H2O