Pp 69 – 73 & 217 - 237
3.7 Cell respiration (Core)
 3.7.1 Define cell respiration.
 3.7.2 State that, in cell respiration, glucose in the
cytoplasm is broken down by glycolysis into pyruvate, with
a small yield of ATP.
 3.7.3 Explain that, during anaerobic cell respiration,
pyruvate can be converted in the cytoplasm into lactate, or
ethanol and carbon dioxide, with no further yield of ATP.
 3.7.4 Explain that, during aerobic cell respiration,
pyruvate can be broken down in the mitochondrion into
carbon dioxide and water with a large yield of ATP.
8.1 Cell respiration (AHL)
 8.1.1
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State that oxidation involves the loss of electrons from an element,
whereas reduction involves a gain of electrons; and that oxidation
frequently involves gaining oxygen or losing hydrogen, whereas reduction
frequently involves losing oxygen or gaining hydrogen.
8.1.2 Outline the process of glycolysis, including phosphorylation, lysis,
oxidation and ATP formation.
8.1.3 Draw and label a diagram showing the structure of a mitochondrion
as seen in electron micrographs.
8.1.4 Explain aerobic respiration, including the link reaction, the Krebs
cycle, the role of NADH + H+, the electron transport chain and the role of
oxygen.
8.1.5 Explain oxidative phosphorylation in terms of chemiosmosis.
8.1.6 Explain the relationship between the structure of the mitochondrion
and its function.
Define cell respiration
 Cell respiration is the
controlled release of
energy from organic
compounds in cells to
form ATP
 Glucose is the major
substrate for respiration
 Adenosine triphosphates
(ATP) is the molecule
which directly fuels the
majority of biological
reactions.
Why cell respiration?
 Cells require a
constant source
of energy to
perform various
tasks e.g.
 Movement
 Transport
 Division
Types of Respiration
(i) Anaerobic Respiration
(ii) Aerobic Respiration
Occurs in the absence of Oxygen
Occurs in presence of Oxygen
Occurs in the cells’ cytoplasm
Occurs in the cells’ mitochondria
Yields small amount of ATP (2
molecules) per molecule of glucose
Yields large amount of ATP (38
molecules) per molecule of glucose
Involves fermentation of pyruvate to
lactate in muscles/CO2 & ethanol in
plant & yeast
Does not involve fermentation
Adenosine triphosphate (ATP):
 ATP is the chemical
molecule which directly
fuels the majority of
biological reactions
 About 1025 ATP
molecules are hydrolysed
to ADP and inorganic
phosphate (Pi) daily
 ADP is reduced back to
ATP using the free
energy from the
oxidation of organic
molecules
ATP Cycle
Glycolysis and Cell Respiration
 all types of cell respiration
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starts with glycolysis
glycolysis occurs in the
cytoplasm of the cell
1 glucose molecules is
broken down into 2
pyruvate molecules
there is a net production of
2 ATP molecules
glycolysis does not require
oxygen
the fate of pyruvate depends
on presence or absence of
oxygen
Anaerobic Cell Respiration
 anaerobic cell respiration occurs in the
absence of oxygen
 during glycolysis glucose is broken breakdown
in the cytoplasm
 leading to the production of pyruvate,
 production of small amount of energy (2 ATP
molecules per molecule of glucose)
 in muscles, pyruvate is converted into lactic
acid during lactic acid fermentation
 anaerobic respiration occurs in animals during
intense muscular activity
 in yeast & plant cells, pyruvate is converted into
alcohol (ethanol) & CO2 during alcoholic
fermentation
 no additional APT is produced during
fermentation
Outline the process of aerobic respiration
 during glycolysis glucose is
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partially oxidized in the
cytoplasm
small amount ATP produced
during glycolysis
two pyruvate molecules are
formed by glycolysis
pyruvate absorbed into
mitochondrion
pyruvate is broken down in
the mitochondrion in the
presence of oxygen
to produce carbon dioxide &
water
large amount of energy in
form of ATP is produced per
glucose molecule
Forms of oxidation and reduction
 cellular respiration
involves oxidation &
reduction (redox)
reactions
 oxidation involves the
loss of electrons from an
element, gaining oxygen
or losing hydrogen by a
substance
 reduction involves a
gain of electrons, losing
oxygen or gaining
hydrogen by a substance
Summary of oxidation and reduction
Animation: How the NAD+ Works
Process of glycolysis
 glycolysis occurs in cytoplasm of
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the cell & does not require oxygen
hexose sugar (glucose) is
phosphorylated using ATP
hexose biphosphate is split (lysis)
into two triose phosphates
triose phosphates are oxidised by
removal of hydrogen by NAD+
NAD+ is concerted to NADH + H+
there is net gain of 2 ATP
molecules (2 ATP are used & 4
ATP produced)
2 pyruvate molecules are
produced per glucose molecule
undergoing glycolysis
Animation: How Glycolysis Works
Structure of a mitochondrion
 the electron micrograph on
the left shows the structure
of a mitochondrion as seen
under the electron
microscope
 draw a labelled diagram to
show the structure of a
mitochondrion
 explain the relationship
between the structure of
the mitochondrion and its
function
electron micrograph
interpretive drawing
Structural adaptation of mitochondrion to its function
 large inner surface area of
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cristae for respiratory
complexes such as electron
transport chains
matrix contains DNA and
ribosomes for protein
(enzyme) synthesis
it also contains Krebs cycle
enzymes
double membrane(s) isolates
metabolic processes from the
rest of the cytoplasm
small intermembrane space
between inner and outer
membranes allows
accumulation of protons for
chemiosmosis
Aerobic respiration
Stages of aerobic respiration
 aerobic respiration includes
the following:
 glycolysis; basis of aerobic
cell respiration, produces
ATP, reduced coenzymes &
pyruvate
 link reaction; pyruvate is
transported into the matrix
of the mitochondria
 Krebs Cycle;
decarboxylation of carbon
fragments to yield ATP and
reduced coenzymes
 electron transport chain;
reduced coenzymes are used
to generate more ATP
Key players in aerobic respiration
 Glucose: substrate, source
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of fuel
NAD+/FAD+: electron
carriers
Enzymes: mediate entire
process
Mitochondria: site of
aerobic respiration
ATP: principal end
product
Protons/Electrons:
sources of potential energy
Oxygen: final electron
acceptor
Link reaction
 Link reaction forms the link between glycolysis & Krebs cycle
 pyruvate from glycolysis enters a mitochondrion
 enzymes in the matrix of the mitochondria remove one carbon dioxide
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and hydrogen from the pyruvate
hydrogen is accepted by NAD+ to forms NADH + H+
removal of hydrogen is oxidation
removal of carbon dioxide is decarboxylation
the whole process in link reaction is oxidative decarboxylation
the product is an acetyl group which reacts with coenzyme A (CoA) to
form acetyl CoA which enters Krebs cycle
Krebs Cycle
 During Krebs Cycle, also called citric
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acid cycle, oxidative decarboxylation of
the C2 Acetyl group (CH3CO) occurs
yielding ATP, reduced coenzymes &
CO2 is produced as a by-product
Acetyl CoA joins with the C4 acceptor
group - oxaloacetate
CoA is released to transport more
pyruvate into the matrix
A C6 fragment, citrate is formed
C6 Citrate is oxidatively decarboxylated
A C5 group is formed
The Carbon is given off as CO2
NAD+ is reduced to NADH + H+
The C5 fragment is oxidised and
decarboxylated further to a C4
compound
Again the carbon removed forms CO2
NAD+ is further reduced to NADH + H+
The final stage in the cycle has the C4
acceptor regenerated
There is a reduction of NAD+ to NADH
+ H+
FAD (Coenzyme)is reduced to FADH2
ADP is reduced to ATP
Animation: How the Krebs Cycle Works
Oxidative phosphorylation in terms of chemiosmosis
Oxidative phosphorylation
 oxidative phosphorylation occurs
during the electron transport chain
 electrons are passed between electron
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carriers
this occurs in cristae of mitochondria
releasing energy
the energy released is used to move
protons against their concentration
gradient
into the intermembrane space
between the two membranes
finally, the protons join with oxygen
to produce water
protons flow back to the matrix
through the enzyme, ATP synthase
this movement of protons (hydrogen
ions ) down the concentration
gradient is called chemiosmosis
energy is released from chemiosmosis
which produces more ATP (i.e.
combines ADP and Pi)
Chemiosmosis
 There is high concentration
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of H+ in the intermembrane
space & lower concentration
in the matrix
ATP synthetase is an enzyme
embedded in the cristae
membrane
H+create an electrochemical
gradient (chemical potential
energy)
The H+ passes through a
channel in the enzyme
driving the motor
The motor spins generating
energy which bringing
together ADP and Pi to
produce ATP
Animation: Electron Transport System and
ATP Synthesis
Animation: Electron Transport System and
Formation of ATP
Control of Cellular Respiration
 The important switch in the
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control of respiration is the
enzyme phosphofructokinase
This enzyme catalyzes step 3
of glycolysis
Phosphofructokinase is
inhibited by ATP and
stimulated by ADP or AMP.
An example of end-product
inhibition in control of
metabolic pathway
It is also inhibited by citric
acid. This synchronizes the
rates of glycolysis and the
Krebs Cycle
"Cell Respiration" - Cellular Respiration Song
Self Assessment Questions (SAQs)
 Define the term cell respiration [2]
 Outline the process of anaerobic cell
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respiration in yeast
[6]
Outline the process of aerobic cell
respiration
[6]
Outline the process of glycolysis [5]
Draw labelled diagram of a
mitochondrion as seen in an
electron micrograph
[5]
Explain the relationship between the
structure of the mitochondrion and
its function
[5]
Explain oxidative phosphorylation in
terms of chemiosmosis
[9]