Unit 1
Communication, Homeostasis and Energy
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What is aerobic respiration?
What is anaerobic respiration?
Which organelle carries out most of
the stages of respiration in eukaryotic
cells?
What are the products of aerobic
respiration?
What is the universal energy currency
molecule?
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Outline why plants, animals and
microorganisms need to respire, with
reference to active transport and
metabolic reactions.
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In order to maintain life, organisms
need a source of energy.
In most organisms this is provided by
the oxidation of organic molecules.
Autotrophic nutrition
 Synthesise organic materials from
inorganic sources e.g. photosynthesis
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Heterotrophic nutrition
 Obtained in organic form
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Energy is the ability to do work
Energy exists in two states
 Kinetic energy
▪ Energy of motion
 Potential energy
▪ Stored energy
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Energy facts
 Cannot be created or destroyed
 Can be converted from one form to
another
 Takes a variety of forms
 Measured in joules or kilojoules
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Metabolism
 All reactions that take place within the
organism
 Anabolism
▪ Build up of larger, more complex molecules
from smaller, simpler ones
 Catabolism
▪ Breakdown of complex molecules into smaller,
simpler ones
▪ Releases energy
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“Work”
 Synthesis of complex substances
 Active transport e.g. sodium-potassium pump
 Movement
 Bioluminescence
 Maintenance of body temperature
 Production of electricity
 Maintenance, repair and division
 Activation of chemicals
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Energy is defined as the ability to do
________________.
The energy of motion is known as
___________ energy, whereas _________
energy is stored energy.
Living organisms need energy for many
reasons
 __________ reactions in which simple
molecules are built up into complex ones
 The movement of material by __________
against a concentration gradient.
Fireflies can produce light in a
process called bioluminescence.
Outline the energy transformations
that occur in fireflies as they use
energy from their food to produce
luminescence.
Comment on the statement below.
1.
2.
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Respiration produces energy to form ATP.
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Describe, with the aid of diagrams, the
structure of ATP.
State that ATP provides the immediate
source of energy for biological
processes.
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ATP is a phosphorylated nucleotide.
 Adenosine
▪ Adenine
▪ Ribose sugar
 Three phosphate groups
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Covalent bonds between phosphate
groups are unstable and easily broken
releasing energy
▪ ATP 
▪ ADP 
▪ AMP 
ADP
= 30.6kJmol-1 (energy)
AMP
= 30.6kJmol-1(energy)
Adenosine = 14.2kJmol-1 (energy)
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As ATP is hydrolysed energy is
immediately available to the cell in
small, manageable amounts.
ATP is described as the universal
energy currency.
ATP is continually being hydrolysed
and resynthesised.
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What type of base is adenine?
ATP is a nucleic acid / nucleotide
derivative.
 Is it derived from DNA or RNA nucleotides?
 Give reasons for your answer
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Explain why ATP is known as the
universal energy currency.
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explain the importance of coenzymes
in respiration, with reference to NAD
and coenzyme A;
state that glycolysis takes place in the
cytoplasm
outline the process of glycolysis;
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The oxidation of food to obtain free
energy (ATP)
Respiration of glucose can be
summarised in four stages
 Glycolysis
 The link reaction
 Krebs cycle
 Oxidative Phosphorylation
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Oxidation
 Loss of electrons
 Loss of hydrogen atoms
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OIL RIG
Reduction
 Gain of electrons
 Gain hydrogen atoms
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If one substrate becomes oxidised
another becomes reduced.
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During respiration, hydrogen atoms
are removed from substrate molecules
in oxidation reactions.
This is catalyzed by dehydrogenase
enzymes
Co enzymes are required to activate
the oxidation reactions in respiration
 Hydrogen atoms becomes attached to
co enzymes e.g. NAD
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Nicotinamide adenine dinucleotide
(NAD
 Is reduced when it has accepted two
hydrogen atoms with their electrons
 Operates in glycolysis, link reaction, the
Krebs cycle and the anaerobic pathways.
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Function
 To carry ethanoate (acetate) groups
made in the link reaction, onto the Krebs
cycle
 To carry acetate groups made from fatty
acids or amino acids onto the Krebs cycle
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Ancient biochemical pathway
Glucose (6C) is broken down into two
molecules of pyruvate (3C), with a net
gain of 2 ATP molecules.
Occurs in the cytoplasm
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Pathway can be outlined in four
stages
 Phosphorylation
 Splitting of hexose 1,6-bisphosphate
 Oxidation of triose phosphate
 Conversion of triose phosphate to
pyruvate
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Net gain of two ATP molecules
Two molecules of reduced NAD
Two molecules of pyruvate
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Enzymes that cause the shape of a
molecule to change (without
changing in proportions of atoms in
that molecule) are called isomerases.
 At which stage of glycolysis are isomerase
enzymes involved?
 How does the fact the nearly all living
things use the glycolysis pathway support
the theory of evolution?
recall the structure of a liver mitochondrion
identify inner and outer membranes and
the inter membranal space
 state that, during aerobic respiration in
animals, pyruvate is actively transported
into mitochondria;
 explain, with the aid of diagrams and
electron micrographs, how the structure of
mitochondria enables them to carry out
their functions;
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All mitochondria have an inner and
outer phospholipid membrane
(envelope)
Inner membrane is folded into cristae
Intermembrane space
Matrix
 Contains looped DNA
 Mitochondrial ribosomes
 enzymes
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This is where the link reaction and the
Krebs cycle take place
It contains
 Enzymes
 Molecules of coenzyme NAD
 Oxaloacetate
 Mitochondrial DNA
 Mitochondrial ribosomes
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It contains
 Protein channels or carriers to allow
pyruvate to pass through
 Other proteins act as enzymes
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Has a different membrane structure
and is impermeable to small ions (e.g.
hydrogen ions)
Folded into cristae to give a large
surface area
Contains electron carriers and ATP
synthase enzymes
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It has been suggested that
mitochondria are derived from
prokaryotes. What features of their
structure support this suggestion?
Suggest how the structure of a
mitochondria from a skin cell would
differ from that of a mitochondrion
from heart muscle tissue.
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state that the link reaction takes place
in the mitochondrial matrix;
outline the link reaction, with
reference to decarboxylation of
pyruvate to acetate and the
reduction of NAD;
explain that acetate is combined with
coenzyme A to be carried to the next
stage;
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Pyruvate is actively transported into
the matrix of the mitochondria.
Pyruvate is dehydrogenated and
decarboxylated to acetate in a series
of enzyme controlled reactions.
Enzymes
 Pyruvate dehydrogenase
 Pyruvate decarboxylase
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NAD accepts the hydrogen ions
Coenzyme A accepts acetate to form
Acetyl CoA, to carry onto the Krebs
cycle.
Carbon dioxide is released
state that the Krebs cycle takes place in the
mitochondrial matrix;
 outline the Krebs cycle, with reference to
the formation of citrate from acetate and
oxaloacetate and the reconversion of
citrate to oxaloacetate
 explain that during the Krebs cycle,
decarboxylation and dehydrogenation
occur, NAD and FAD are reduced and
substrate level phosphorylation occurs
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Takes place in the mitochondrial
matrix
Main stages
 Decarboxylation
▪ Removal of Co2
 Dehydrogenation
▪ reduction of NAD
 Substrate-level phosphorylation
▪ Production of ATP
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For each original glucose molecule
there are two turns of the Krebs cycle.
Products
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6 reduced NAD
2 reduced FAD
4 carbon dioxide
2 ATP
Although oxygen is not used up in these
stages, they can not take place if it is
absent – they are aerobic stages
Product per
molecule of
glucose
Reduced NAD
Reduced FAD
CO2
ATP
Glycolysis Link
reaction
Krebs
cycle
Product per
molecule of
glucose
Reduced NAD
Glycolysis Link
reaction
Krebs
cycle
2
2
6
Reduced FAD
0
0
2
CO2
0
2
4
ATP
2
0
2
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Moving into the last stage of aerobic
respiration
 10 reduced NAD
 2 reduced FAD
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Explain why mature erythrocytes
cannot carry out the link reaction or
Krebs cycle
The inner mitochondrial membranes are
impermeable to reduced NAD. For this
reason a shunt mechanism moves hydrogen
ions from reduced NAD made during
glycolysis, to the matrix side of the inner
mitochondrial membrane. The hydrogens are
carried in by another chemical than then
becomes reoxidised, reducing NAD that is
already in the mitochondrial matrix.
 Explain why such a shunt mechanism is not
required for NAD reduced during the link
reaction and Krebs cycle.
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Aerobic prokaryotes can carry out the
link reaction, Krebs cycle and
oxidative phosphorylation.
Suggest where in the prokaryotic cell
these reactions take place.
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outline the process of oxidative
phosphorylation, with reference to the
roles of electron carriers, oxygen and
the mitochondrial cristae;
state that oxygen is the final electron
acceptor in aerobic respiration;
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Formation of ATP by adding a
phosphate group to ADP
Takes place in the presence of oxygen
Oxygen is the final electron acceptor
Takes place across the inner
mitochondrial membrane
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Reduced NAD and reduced FAD are
reoxidised when they donate the
hydrogen, split into H+ and eElectrons are accepted by electron
carriers
Protons go into solution in the matrix
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Electrons passed along chain of
carriers, energy released is used to
pump protons across to
intermembrane space
building up a proton/ pH /
electrochemical gradient
Hydrogens diffuse through ion
channels associated with ATPsynthase
(chemiosmosis)
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As protons flow through ATP synthase
 Drive the rotation of part of enzyme
 This joins ADP and Pi to form ATP
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Electrons and hydrogen ions combine
with oxygen to form water.
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outline the process of chemiosmosis,
with reference to the electron
transport chain, proton gradients and
ATPsynthase
evaluate the experimental evidence
for the theory of chemiosmosis
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The complete oxidation of one molecule of
glucose produces a net yield of 32 ATP’s.
Energy required to make ATP comes from:
 Respiration – energy released by rearranging chemical
bonds
 The transfer of electrons by electron carriers in
mitochondria
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H+ ions create a concentration gradient through a
protein channel;
 this protein channel acts as the enzyme ATP synthase.
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3 H+ ions provide the energy to make one ATP
molecule, provided that ADP and Pi are available.
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Build of hydrogen ions on one side of
membrane is a source of potential
energy
Movement of ions across the
membrane down an electrochemical
gradient – provides energy to form ATP
from ADP and Pi.
Inner mitochondrial membrane =
energy transducing membrane
Kinetic energy of the flow of ions =
proton motive force
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On the hand out – write out how each
piece of evidence supports the
chemiosmosis theory put forward by
Mitchell in 1961.
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pH gradient across the membranes in
involved in ATP production
 The pH on one side of the membrane is
higher than the other
 This suggests hydrogen ions are being
actively moved across the membrane
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Membranes make ATP even if there is
no electron transport taking place, as
long as a pH gradient is produced.
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Explain why was it important to keep
the thylakoids in the dark?
Explain why the pH inside and outside
the thylakoid membranes becomes
equal when they are left in pH4 buffer
for some time.
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Does a pH4 buffer contain a greater
or smaller concentration of H+ than a
pH8 buffer?
In which direction was there a pH
gradient when the thylakoids were
place in the pH8 buffer?
Explain why and how the thylakoids
were able to make ATP when they
were placed in the pH8 buffer solution.
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Chemicals that prevent hydrogen ions
being transported across the
membrane also stop ATP being
produced.
 Dinitrophenol is a chemical that acts as a
hydrogen carrier across membranes.
 If Dinitrophenol is added – no hydrogen
ion gradient is built up.
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The hydrogen ion gradient is
responsible for making ATP not the
electron transport.
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explain why the theoretical maximum
yield of ATP per molecule of glucose is
rarely, if ever, achieved in aerobic
respiration;
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Summary aerobic respiration
 Glucose is oxidised to pyruvate in
glycolysis
 Pyruvate is oxidised in Krebs Cycle
 Hydrogen ions removed are passed along
the electron transport chain
▪ For every two hydrogen donated to the ETC by
reduced NAD – 3 ATP molecules are made
▪ For every two hydrogen donated to the ETC by
reduced FAD – 2 ATP molecules are made
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Some energy has been put in to these
processes.
 For every two hydrogen donated to the
ETC by reduced NAD – 2.5 ATP molecules
are made
 For every two hydrogen donated to the
ETC by reduced FAD – 1.5 ATP molecules
are made
ATP
used
process
Phosphorylation of glucose
Glycolysis
Direct phosphorylation of ADP
From reduced NAD
Link
reaction
From reduced NAD
Direct phosphorylation of ADP
Krebs
cycle
From reduced NAD
From reduced FAD
Totals
Net yield
ATP
produced
process
Phosphorylation of glucose
Glycolysis
Link
reaction
Krebs
cycle
ATP
used
ATP
produced
2
Direct phosphorylation of ADP
4
From reduced NAD
5
From reduced NAD
5
Direct phosphorylation of ADP
2
From reduced NAD
15
From reduced FAD
3
2
Totals
Net yield
34
32
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Transport ADP into mitochondria from
the cytoplasm
Transport ATP from mitochondria into
the cytoplasm
Protons could “leak” across
membrane reducing the number to
generate the proton motive force.
Active transport of pyruvate into
mitochondria
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Read the information supplied at the
top of the practical sheet.
Set up the three test tubes as shown
below.
▪ 10ml glucose
▪ 10ml yeast
▪ 5 ml dye
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Shake tubes vigorously for 20 seconds,
and place in a water bath set at 37oC.
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Leave for a few minutes
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Write up the experiment using the
back of the sheet.
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Tube A
 Colour change from blue via pink to
colourless.
 Hydrogen has been rapidly released and
has reduced the dye.
 For this to happen – dehydrogenase
enzymes present in yeast cells must have
acted on the glucose, the respiratory
substrate, and oxidised it.
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Tube B
 Change from blue – pink – colourless
 Reaction is slower since no glucose was added.
 Dehydrogenase could only act on any small
amount of respiratory substrate already present in
the yeast cells.
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Tube C
 Boiling has killed the yeast and denatured the
dehydrogenase enzymes.
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explain why anaerobic respiration
produces a much lower yield of ATP
than aerobic respiration;
compare and contrast anaerobic
respiration in mammals and in yeast;
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Occurs when free oxygen is not
available
oxygen is no longer the final hydrogen
acceptor
Reduced NAD cannot be recycled to
NAD
The stages of respiration inside the
mitochondrion can not take place
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Two other pathways recycle the
reduced NAD formed during glycolysis
 Alcoholic fermentation
▪ Conversion of pyruvate to ethanol
 Lactate fermentation
▪ Conversion of pyruvate to lactate
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Both pathways are inefficient and
provide a net gain of two ATP
molecules per glucose molecule
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Pyruvate is decarboxylated to form
ethanal
Ethanal accepts hydrogen from
reduced NAD to form ethanol
The alcoholic fermentation pathway is
irreversible
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Pyruvate accepts the hydrogen and is
converted into lactate
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The lactate pathway is reversible by
the Cori cycle in the mammalian liver
Lactate causes a fall in pH which may
stop the muscles from contracting.
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define the term respiratory substrate;
explain the difference in relative
energy values of carbohydrate, lipid
and protein respiratory substrates
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Molecules from which energy can be
liberated to produce ATP in a living
cell.
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Below are 3 respiratory substrates and
their energy value
 Glucose
 Lipid
 Protein
16kJg-1
39kJg-1
17kJg-1
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Fatty acids enter the Krebs cycle after
being broken down into two Acetyl
CoA molecules
Amino acids are deaminated
 Converted either into pyruvate and enter
the link reaction or acetate and enter the
Krebs cycle
Glycogen or starch
Protein
Glucose
Lipid
Amino Acids
Pyruvate
fatty Acids
Acetylcoenzyme A
Krebs cycle
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The more hydrogens there are in the
structure of a molecule, the greater
the energy value
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Revise the structure of glucose, amino
acids and fatty acids from the AS
course.
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The respiratory quotient (RQ) is the
ratio of the volumes of oxygen
absorbed and carbon dioxide given
off in respiration.
RQ = Volume of carbon dioxide given off
Volume of oxygen taken in
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Calculate the RQ for the aerobic
respiration of Glucose.
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Calculate the RQ for the fatty acid
oleic acid, when respired aerobically.
 C18H34O2+ 25.5O2  18 CO2 + 17 H2O
C6H12O6  2C2H5OH + 2CO2
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A high RQ value suggests that anaerobic
respiration is taking place.
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No RQ can be calculated for the lactate
pathway as no carbon dioxide is given off.
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The respiratory quotients of different respiratory
substrates are well documented from previous
investigations.
 Carbohydrate
 Protein
 Fat
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1.0
0.9
0.7
It is possible to deduce which substrate is being
used by the metabolism at a specific time.
 NB if a mixture of substrates is being used then the
figure will be different from those above.
Sodium hydroxide absorbs all CO2 from
the air in the apparatus from the
beginning.
 As the germinating seeds use oxygen
and the pressure reduces in tube A so
the manometer level nearest to the
seeds rises.
 Any CO2 excreted is absorbed by the
sodium hydroxide solution.

The syringe is used to return the manometer
fluid levels to normal.
 The volume of oxygen used is calculated by
measuring the volume of gas needed from
the syringe to return the levels to the original
values
 If water replaces the sodium hydroxide then
amount of carbon dioxide given off can be
measured
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The respiratory quotient can be measured.
RQ = x + y
or
x-z
x
x
 where
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 x is the oxygen consumption
 y is the increase in volume of air (if more CO2 is
produced than oxygen taken in)
 z is the decrease in the volume of air (if less CO2 is
produced than oxygen taken in)