AP Biology
Cellular Respiration
Notes
9.1
Distinguish between fermentation and cellular respiration.
Fermentation
anaerobic (without O2)
cytoplasm
Produces ATP
Partial degradation
9.2
Cellular Respiration
aerobic (with O2).
mitochondria
Produces 18x more
ATP
Complete degradation
More efficient &
widespread
Provide the overall chemical equation for cellular respiration.
Compare the efficiency of this process in cells to the efficiency of
a gasoline automobile engine.
C6H12O6 + 6 O2  6 CO2 + 6H2O + energy (ATP + heat)



40% of the energy in 1 glucose is converted into the chemical energy
of 38 ATP.
25% of the energy in gasoline is converted to kinetic energy.
Exergonic with G of -686kcal / mole glucose
9.3
Define oxidation and reduction.
Redox Reactions: release energy when electrons move closer to
electronegative atoms.
9.4



Explain in general terms how redox reactions are involved in
energy exchanges.
Catabolic pathways transfer the electrons stored in food molecules,
releasing energy that is used to synthesize ATP.
Reactions that result in the transfer of one or more electrons from one
reactant to another are oxidation-reduction reactions, or redox reactions.
(Use “Stair step ETC” transparency)
o The loss of electrons is called oxidation. (Oxid.# increases)
o The addition of electrons is called reductions. (Oxid.# is
reduced)
In order to follow the energy you need only to “Follow the electrons.”
9.5 Describe the role of NAD+ in cellular respiration.
NAD+ is a coenzyme (nicotinimide adenine dinucleotide)
NAD+ is an oxidizing agent (i.e. it picks up electrons from molecules that are
then oxidized)
NAD+ is an electron carrier. It shuttles electrons to the ETC.
Dehydrogenase is the enzyme that strips 2 e- and 2 H+ from organic
molecules during the Krebs cycle.

NAD+ picks up two electrons and one hydrogen ion (proton) leaving the
other H+ in solution.

NADH shows the one hydrogen that was picked up.

The two e- make it neutral.
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9.6 In general terms, explain the role of the electron transport chain in
cellular respiration.

To harness the energy in the electrons,

the electrons are only allowed to decrease their distance from a nucleus a
little bit at a time

by passing the electron to increasingly electronegative molecules in the
ETC. In so doing, H+ are translocated across the membrane

to create the proton (H+) gradient which will be used to

drive the Phosphorylation of ADP to ATP using ATPsynthase.
9.7
List the cellular regions where glycolysis, the citric acid cycle, and
oxidative phosphorylation occur. Note whether substrate-level
phosphorylation or chemiosmosis occur at each of these sites.
Location
Glycolysis
Citric acid
cycle
Oxidative
phosphorylation
cytoplasm
matrix of
mitochondion
across the
inner
membrane
Substrate-Level
Phoshorylation?
Yes
Chemiosmosis?
No
Yes
No
No
Yes
9.7
Compare the reactants, products, and energy yield of the three
stages of cellular respiration.
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Reactants
1. Glycolysis
Glucose
2 ATP
2. Citric Acid
Cycle
2 Pyruvate 
2 Acetyl CoA +
2 CO2
3. Oxid.
Phosph.
Oxygen
12 NADH
2 FADH2
Products
2 Pyruvate
2 NADH
4 ATP
(2 NADH)
6 NADH
2 FADH2
2 ATP
2 CO2
34 ATP
Energy Yield
in # of ATP
2
2
34
total = 38 ATP
9.9 Explain why ATP is necessary for the
preparatory steps of Glycolysis.

It is used to create a charge on the sugar
which traps it in the cell.

2 ATP are required as Eact for the splitting of
glucose.
9.10 Identify where substrate-level
Phosphorylation and the reduction of
NAD+ occur in Glycolysis.

They occur in the energy payoff phase
9.11 Describe where pyruvate is oxidized to
acetyl CoA, what molecules are produced,
and how this process links Glycolysis to
the citric acid cycle.

Occurs in the Matrix

Products: CO2 + NADH + H+ + Acetyl CoA

The acetyl group of Acetyl CoA will enter the
Krebs cycle linking it to Glycolysis.
9.12 List the products of the citric acid cycle. Explain why it is called a
cycle.

Products: 2 CO2 + 3 NADH + 3 H+ + ATP + FADH2

To calculate the inputs and outputs on a per-glucose basis, multiply by 2,
because each glucose molecule is split during Glycolysis into two pyruvate
molecules.

The carbon atoms that enter the cycle from acetyl CoA do not leave the
cycle in the same turn.

They remain in the cycle, occupying a different location in the molecules
on their next turn after another acetyl group is added.
How many times does the Citric Acid cycle turn to completely oxidize
one glucose molecule?
9.13 Describe the point at which glucose is completely oxidized during
cellular respiration.

When it is all converted to CO2.

This will require three turns of the cycle.
9.14 Distinguish between substrate-level Phosphorylation and oxidative
Phosphorylation.

Substrate-level: the formation of ATP by directly transferring a phosphate
group to ADP from an intermediate substrate in catabolism.
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
Oxidative: The production of ATP using energy derived from the redox
reactions of an electron transport chain. (Creating a H+ gradient and using
it to drive ATP Synthase.)
9.15 In general terms, explain how the exergonic “slide” of electrons
down the electron transport chain is coupled to the endergonic
production of ATP by chemiosmosis.
1. Electrons are made available in the Citric Acid cycle.
2. The first protein in the ETC is reduced when it accepts e-‘s
3. The proteins of the ETC are arranged by increasing electronegativity
4. The proteins pull the e- back and forth across the membrane “exergonic
slide” and translocate H+ in one direction creating a hydrogen ion
gradient.
5. Hydrogen ions flow down their gradient thru ATP synthase driving the
endergonic production of ATP.
9.16 Describe where and how the respiratory electron transport chain
creates a proton gradient.
Where: High hydrogen ion concentration is formed in the intermembrane
space while low hydrogen ion concentration is in the matrix of the
mitochondrion.
How: The proteins of the ETC are arranged by increasing electronegativity.
The proteins pull the e- back and forth across the membrane “exergonic
slide” and translocate H+ in the intermembrane space creating a
hydrogen ion gradient with the matrix.
9.17 omit
9.18 Summarize the net ATP yield from the oxidation of a glucose
molecule by constructing an ATP ledger.
See 9.7
9.19 omit
9.20 State the basic function of fermentation
To produce ATP in the absence of oxygen.

Fermentation is an extension of Glycolysis.

Fermentation allows for the recycling of NAD+ so that Glycolysis can
continue to be oxidized.

Glucose becomes oxidized by losing e- to NAD+ and making
NADH.

NADH is oxidized by losing e- to the product of fermentation
(reducing it) and becoming NAD+ again.
9.21 Compare the fate of pyruvate in alcohol fermentation and in lactic
acid fermentation.

Alcohol fermentation produces 2 carbon dioxide and 2 ethanol

Lactic Acid fermentation produces 2 lactate (reduced lactic acid)
9.22 Compare the processes of fermentation and cellular respiration.

Both use Glycolysis to oxidize glucose, but differ in their final electron
acceptor.

Aerobic Respiration yields 18x more ATP
9.23 Describe the evidence that suggests that Glycolysis is an
ancient metabolic pathway.

Gycolysis exists in nearly all organisms- it evolved early and was
passed down
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


Occurs in cytoplasm therefore does not require membrane-bound
organelles, eukaryotes evolved 1 billion years after prokaryotes
For nearly 1 billion years prokaryotes used glycolysis to make ATP
because it does not need oxygen.
Metabolic “heirloom” still functions in fermentation and first step in cellular
respiration.
Explain how the human body uses its daily supply of ATP.
Minimum functions (maintenance) = 75% of calories taken in each day
Voluntary Activity = varies according to activity
9.24 Describe how food molecules other than glucose can be oxidezed
to form ATP.


(Explain how polysaccharides, fats, and proteins are used as fuel for
cellular respiration. Explain why a gram of fat yields
more ATP than a gram of starch or protein.)
The process of hydrolyzing (breaking down) carbs, lipids
and proteins creates the smaller molecules that fit into the
process of cellular respiration at appropriate steps.
One gram of fat contains more calories than one gram of
polysaccharides or proteins.
9.25 Explain how Glycolysis and the citric acid cycle can
contribute to anabolic pathways. (Explain how
nutrients are used in biosynthesis.)
Intermediate molecules from the breakdown of glucose can be
tapped as building blocks that the cell needs.
Examples:

Monosaccharides  polysaccharides (starch, cellulose)

Fatty acids and glycerol  lipids

Amino acids  polypeptides (protein like muscle or
enzymes)
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9.26 Explain how ATP production is controlled by the cell, and describe
the role that the allosteric enzyme phosphofructokinase plays in the
process.

Phosphofructokinase is an allosteric enzyme that responds to inhibitors
and activators that help set the pace of Glycolysis and the citric acid cycle.

Stimulated by: AMP (meaning it is low on ATP)

Inhibited by products: ATP and citrate (4+2 = citrate or citric acid)
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