Chapter 9
Chemical Energy and Food
 Living things get the energy they need from food.
 The process of releasing the energy stored in food is
cellular respiration.
Overview of Cellular Respiration
 In the presence of oxygen, aerobic respiration takes
place.
 This produces 36 ATP per molecule of glucose.
 In the absence of oxygen, anaerobic respiration
(fermentation) takes place.
 This produces 2 ATP per molecule of glucose.
Section 9-1
Chemical Pathways
2
2
32
Glycolysis
Krebs
cycle
Electron
transport
Alcohol or
lactic acid
Anaerobic
Fermentation
(without oxygen)
Aerobic
Glucose
Glycolysis
 Both aerobic and anaerobic respiration begin with a
process known as glycolysis.
 This means “glucose -splitting”
 This takes place in the cytoplasm.
Section 9-1
Glycolysis
Glucose
2 Pyruvic acid
To the electron
transport chain
Glycolysis
 If oxygen is available, the pyruvic acid molecules will
be broken down further to release more energy.
 This is called aerobic respiration.
 If oxygen is unavailable, the pyruvic acid molecules
will be converted to a waste product with no further
release of energy.
 This is called anaerobic respiration, or fermentation.
Anaerobic Respiration
(Fermentation)
 Takes place in the cytoplasm without oxygen.
 Two types:
 Alcoholic fermentation – in yeasts

Pyruvic acid is converted to alcohol and carbon dioxide.
 Lactic acid fermentation – in bacteria and muscle cells

Pyruvic acid is converted to lactic acid.
Section 9-1
Lactic Acid Fermentation
Glucose
Pyruvic acid
Lactic acid
Alcoholic Fermentation
Aerobic Respiration
 In the presence of oxygen, pyruvic acid is further
broken down to release additional energy.
 This takes place in the mitochondria.
 There are two steps:
The Krebs Cycle
2. The electron transport chain
1.
Mitochondrial Reactions
Mitochondrion
Electrons carried in NADH
Pyruvic
acid
Glucose
Glycolysis
Krebs
Cycle
Electrons
carried in
NADH and
FADH2
Electron
Transport
Chain
Mitochondrion
Cytoplasm
The Krebs Cycle
 Also known as the citric acid cycle.
1. Pyruvic acid (from glycolysis) is broken down into
carbon dioxide.
2. High energy electrons are captured by NAD and FAD
and brought to the electron transport chain.
 Net gain of 2 ATP from this cycle.
 This occurs in the matrix of the mitochondrion.
Section 9-2
The Krebs Cycle
Citric Acid
Production
Mitochondrion
Electron Transport Chain
 NADH and FADH2 drop off high energy electrons.
 These pass through a series of reactions located on the
inner membrane that produce ATP.
 At the end, oxygen combines with hydrogen to make
water.
 Net gain of ATP = 32
Electron Transport Chain
Section 9-2
Electron Transport
Hydrogen Ion Movement
Channel
Mitochondrion
Intermembrane
Space
ATP synthase
Inner
Membrane
Matrix
ATP Production
ATP totals
 Glycolysis – 2
 Krebs Cycle – 2
 Electron Transport Chain – 32
 Net: from one glucose molecule = 36 ATP
Aerobic Respiration
Net Reaction:
 6O2 + C6H12O6  6CO2 + 6H2O + 36 ATP
 Oxygen + glucose  carbon dioxide + water + energy
Photosynthesis & Cellular
Respiration
Photosynthesis
Cellular Respiration
Function
Energy capture
Energy release
Location
Chloroplasts
Mitochondria
Reactants
CO2 & H2O
C6H12O6 & O2
Products
C6H12O6 & O2
CO2 and H2O
Equation
6CO2 + 6H2O  C6H12O6
+ 6O2
6O2 + C6H12O6  6CO2 +
6H2O