1. Photosynthesis in chloroplasts Cellular respiration in mitochondria
Figure 9.2
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
 O2
Organic molecules
CO2  H2O
Cellular respiration in mitochondria
Figure 9.2 Energy flow and chemical recycling in ecosystems.
ATP powers most cellular work
ATP
Heat energy

2. Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
Several processes are central to cellular respiration and related pathways
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3. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic
Fermentation is a partial degradation of sugars that occurs without O2
Aerobic respiration consumes organic molecules and O2 and yields ATP
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2
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4. C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
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5. Redox Reactions: Oxidation and Reduction
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
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6. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
In oxidation, a substance loses electrons, or is oxidized
In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
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7. becomes oxidized (loses electron) becomes reduced (gains electron)
Figure 9.UN01
becomes oxidized (loses electron)
becomes reduced (gains electron)
Figure 9.UN01 In-text figure, p. 164

8. becomes oxidized becomes reduced
Figure 9.UN02
becomes oxidized
becomes reduced
Figure 9.UN02 In-text figure, p. 164

9. The electron donor is called the reducing agent
The electron receptor is called the oxidizing agent
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
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10. Methane (reducing agent) Oxygen (oxidizing agent)
Figure 9.3
Reactants
Products
becomes oxidized
Energy
becomes reduced
Figure 9.3 Methane combustion as an energy-yielding redox reaction.
Methane (reducing agent)
Oxygen (oxidizing agent)
Carbon dioxide
Water

11. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced
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12. becomes oxidized becomes reduced
Figure 9.UN03
becomes oxidized
becomes reduced
Figure 9.UN03 In-text figure, p. 165

13. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps
Electrons from organic compounds are usually first transferred to NAD+, a coenzyme
As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
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14. Nicotinamide (oxidized form) Nicotinamide (reduced form)
Figure 9.4
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Oxidation of NADH
Nicotinamide (oxidized form)
Nicotinamide (reduced form)
Figure 9.4 NAD as an electron shuttle.

15. Figure 9.UN04
Dehydrogenase
Figure 9.UN04 In-text figure, p. 166

16. NADH passes the electrons to the electron transport chain
Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction
O2 pulls electrons down the chain in an energy-yielding tumble
The energy yielded is used to regenerate ATP
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17. Controlled release of energy for synthesis of ATP
Figure 9.5
H2  1/2 O2
2 H 
1/2 O2
(from food via NADH)
Controlled release of energy for synthesis of ATP
2 H+  2 e
ATP
Explosive release of heat and light energy
ATP
Electron transport chain
Free energy, G
Free energy, G
ATP
2 e
1/2 O2
Figure 9.5 An introduction to electron transport chains.
2 H+
H2O
H2O
(a) Uncontrolled reaction
(b) Cellular respiration

18. The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose has three stages
Glycolysis (breaks down glucose into two molecules of pyruvate)
The citric acid cycle (completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of the ATP synthesis)
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19. Glycolysis (color-coded teal throughout the chapter) 1.
Figure 9.UN05
Glycolysis (color-coded teal throughout the chapter) 1.
Pyruvate oxidation and the citric acid cycle (color-coded salmon) 2.
Oxidative phosphorylation: electron transport and chemiosmosis (color-coded violet) 3.
Figure 9.UN05 In-text figure, p. 167

20. Electrons carried via NADH Electrons carried via NADH and FADH2
Figure 9.6-3
Electrons carried via NADH
Electrons carried via NADH and FADH2
Oxidative phosphorylation: electron transport and chemiosmosis
Pyruvate oxidation
Glycolysis
Citric acid cycle
Glucose
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
Figure 9.6 An overview of cellular respiration.
ATP
ATP
ATP
Substrate-level phosphorylation
Substrate-level phosphorylation
Oxidative phosphorylation

21. The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
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22. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP
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23. Enzyme Enzyme ADP P Substrate ATP Product
Figure 9.7
Enzyme
Enzyme
ADP P
Substrate
ATP
Figure 9.7 Substrate-level phosphorylation.
Product