AL Bio notes Respiration
P.1
RESPIRATION
O
rganisms maintain themselves by the continual expenditure of energy. Most cells derive this
energy from the breakdown of food molecules, a process known as cellular or internal
respiration. Substances that are broken down to yield energy are called respiratory substrates.
In most organisms glucose is broken down to carbon dioxide and water in a process which requires
molecules of oxygen, and is known as aerobic respiration.
C6H12O6
glucose
+
602
oxygen
6C02
+
carbon dioxide
6H2O
water
+
energy
In the absence of oxygen molecules, anaerobic respiration takes place in which glucose is partially
broken down, to lactic acid in animals, and to carbon dioxide and alcohol in plants. The latter
process is also called alcoholic fermentation:
anaerobic respiration in plants
C6H12O6
C2H5OH + 2CO2
(ethyl alcohol)
anaerobic respiration in animals
C6H12O6
CH3CHOH.COOH
(lactic acid)
+
C02
+
+
energy
energy
The partial breakdown of glucose in anaerobic respiration yields only a fraction of the chemical
energy stored in the molecule.
Glucose is broken down in a
series of carefully
controlled reactions, during
which energy is made
available in relatively
small amounts which can
be harnessed and made to
perform work.
A much smaller proportion
of the energy in the glucose
molecule is dissipated as
heat compared with
combustion. (at most about
forty per cent).
The energy made available during the respiratory process is stored in molecules of adenosine
triphosphate, usually called ATP.
AL Bio notes Respiration
I)
THE ROLE OF ATP AS A STORE AND SUPPLIER OF ENERGY
ATP occurs in all living cells. It is the un___________
energy 'currency'. All energy-spending activities such as
synthesis, muscle contraction, transmission of nerve
impulses …….., depend on ATP as their im________
source of energy.
Energy is supplied by the splitting of the bond that
attaches the terminal phosphate groups to the rest of
the molecule. The bond is broken by hydrolysis. This
reaction yields a large amount of energy (about 33 kJ
mol-1). Because of this high energy yield, ATP is often
called an 'energy-rich' or 'high-energy' molecule.
ATP thus provides a source of energy that is easily and
rapidly accessible to any energy-requiring process.
Matching : Analogy of Energy availability and Money currency
ATP
glucose
carbohydrate reserves, starch and glycogen
fat reserves
II)








THE FORMATION OF ATP
Molecules of ATP are constantly being 'spent' and must be
replaced. They are formed from ADP and inorganic phosphate
by condensation. This reaction is also a phosphorylation.
The regeneration of ATP requires a supply of energy = that
which it gives on hydrolysis. This is supplied by respiration.
There are two mechanisms that direct the energy yield from
respiration into the formation of ATP; namely s_________-linked
phosphorylation and o___________ phosphorylation.
a)
Substrate-linked phosphorylation
At 3 steps in the respiratory sequence where p________ is
detached from one of the intermediate compounds of glucose
breakdown (the respiratory substrate), together with sufficient
energy to form a bond with ADP. This process is thus
substrate-based or linked and, unlike oxidative phosphorylation,
does not need O2.
b)
Oxidative phosphorylation
This process involves oxidation reactions. Such reactions tend to
have a high ‘energy yield’, and it is this energy that is used to
combine inorganic phosphate and ADP.
Investment accounts
deposit accounts
cash
cheque
P.2
AL Bio notes Respiration
P.3
The following types of reaction are all described as Oxidations:
i) The addition of oxygen to a molecule,
e.g.
C + O2
CO2
(the burning of carbon in air)
ii) The removal of hydrogen from a molecule (dehydrogenation).
e.g.
AH2 + B
A + BH 2
iii) The removal of an electron from a charged ion,
e.g.
Fe ++
-
e (an electron)
Fe
+++
All three types of oxidation are involved in oxidative phosphorylation :
1) Pairs of hydrogen atoms are removed from a number of respiratory intermediates by
dehydrogenase enzymes; the respiratory intermediates are thus oxidised.
2) The hydrogen removed is transferred to hydrogen-acceptors, usually nicotinamide adenine
dinucleotide (NAD+). These molecules are also described as coenzymes because they are
essential for the functioning of the dehydrogenase enzymes.
3) The hydrogen is split into protons and electrons on its way through the series of carriers, the
electrons are eventually combined into with oxygen to form water. The whole sequence of
carriers, including the initial hydrogen-acceptors, comprises the Electron transport chain or
Respiratory chain.
c)
Electron Transport Chain (ETC) / The Respiratory Chain
A series of coupled ox_______/re________ reactions where e________ are passed like hot potatoes
from one membrane-bound p______ to another before being finally attached to a terminal electron
acceptor (o______ in respiration, N________ in photosynthesis ). ATP is formed in the process.
Each of the carriers in the respiratory chain is successively reduced and then oxidised as it first
accepts and then hands on the hydrogen. ETS moves both electrons and protons: electrons are
passed from carrier to carrier in the membrane, while protons are moved from in_____ to out____ of
membrane (inner membrane).
In fact, early in the series of protein carriers, it is only the electrons of the hydrogen atoms that are
passed along the chain. Hydrogen atoms are split into hydrogen ions and electrons.
H
H+
+
e- (an electron)
AL Bio notes Respiration
P.4
Each carrier in this chain has a greater affinity for electrons than its predecessor so there is a
one-way flow of electrons along the chain. In particular the electron transport chain contains several
cytochromes, which are a group of iron-containing proteins (h____ group). The state of the iron is
altered from the oxidised ferric (Fe + + +) form to the reduced ferrous (Fe ++) form, and then back to
the oxidised form as the cytochrome accepts and then passes on electrons.
Fe+++ (oxidized)
cytochrome
+
-
electron
electron
Fe++ (reduced)
cytochrome
At the final cytochromes in the chain, the electrons combine with hydrogen ions, and then combine
with molecules of oxygen to form water.
2H+
+
2e-
2H
2H+
+
O2
H2 O
Incidentally, cyanide exerts its toxic effects by binding cytochrome oxidase so as to prevent the
binding of o______. It thus acts as a respiratory in_________, and in large amounts can rapidly
cause death through energy lack.
The energy yield is on average 3ATP from each NADH entering the ETC.
AL Bio notes Respiration
Reference reading:
P.5
Proton gradient / Chemiosmotic hypothesis (Peter Mitchell, 1961)
As electrons flow through ETC, at certain steps protons (H+) are moved from inside to outside of the
membrane. This builds up proton gradient; since + charges are removed from inside of cell, -ve charge
remains inside, mainly as OH- ions. pH just outside membrane can reach 5.5, pH just inside membrane can
reach 8.5 ---> difference of 3 pH units, or 1000x concentration differential of H+ across membrane. This
represents potential energy stored up in proton gradient.
1.
Protons are translocated across the membrane, from the matrix to the intermembrane space
2.
Electrons are transported along the membrane, through a series of protein carriers
3.
Oxygen is the terminal electron acceptor, combining with electrons and H+ ions to produce water
4.
As NADH delivers more H+ and electrons into the ETS, the proton gradient increases, with H+
building up outside the inner mitochondrial membrane, and OH - inside the membrane.
Membrane is basically impermeable to protons, so gradient doesn't get wasted away by leaky reentry.
ATP synthase protein complex contains only channels for proton entry.
As protons push in through channel :
ADP + Pi ---> ATP.
This can be called chemiosmotic phosphorylation or oxidative phosphorylation.
III)
THE BREAKDOWN OF GLUCOSE
Aerobic and anaerobic respiration share a common initial pathway known as glycolysis (which
means sugar-splitting), in which the glucose is broken down through a series of reactions to pyruvic
acid (2-oxopropanoic). The breakdown of glucose to pyruvic acid takes place in the c_________ and
does not require the presence of oxygen molecules.
An outline of glycolysis
This is the initial pathway shared by both aerobic and anaerobic respiration. The process takes place in the
cytoplasm and is not dependent on the presence of oxygen.
It comprises two stages; in the first, glucose is phosphorylated to fructose disphosphate. After phosphorylation,
the substrates were eventually broken down to two pyruvic acid molecules.
Each of the reactions is catalysed by an enzyme.
AL Bio notes Respiration
P.6
Glucose
Glucose is a rather unreactive molecule. Before it can participate in
the reactions that follow, it must be supplied with activation energy.
This is achieved by two successive phosphorylations to form a
hexose diphosphate (fructose diphosphate).
2ATP
2ADP
Fructose diphosphate
Fructose diphosphate splits into two, interconvertible, 3-carbon
compounds known as triose phosphates.
Glyceraldehyde
phosphate
Dihydroxyacetone
phosphate
NAD+
Triose phosphate is oxidized when Hydrogen is removed by
NAD+ and Inorganic phosphate is added to form
diphosphoglyceric acid (DPGA). The ‘new’ phosphate is joined
to the rest of the molecule by an energy-rich bond. (this bond
derived it’s energy from reorganization of energy within the
molecule).
NADH &
H+
inorganic
phosphate
Diphosphoglyceric acid
ADP
Diphosphoglyceric acid reacts with ADP to form ATP (substrate
linked phosphorylation) and phosphoglyceric acid (PGA).
ATP
Phosphoglyceric acid
The PGA is rearranged to form pyruvic acid. The phosphate is
transferred to ADP forming ATP.(substrate linked phosphorylation)
ADP
ATP
Pyruvic acid
a)
The Energy yield of Glycolysis
Summary of glycolysis
input
output
One glucose
Two pyruvic acid
molecule
molecules
2ATP
(for
phosphorylation of
glucose and
fructose)
4ATP from substrate
level
phosphorylation
Thus in conditions where oxygen is available the net
gain from glycolysis is eight molecules of ATP per
glucose molecule.
2ADP and Pi
2 NAD+
Thus, the net yield is two molecules of ATP per
glucose molecule. However, if oxygen is present the
two pairs of hydrogen atoms removed by NAD+ (one
pair from each triose phosphate) can be passed to the
ETC and will there yield a further six molecules of
ATP (by oxidative phosphorylation).
(NADH & H+ ) X 2
The fate of pyruvic acid differs according to whether oxygen is present or not and, in the latter
circumstance, according to whether plant or animal cells are being considered.
AL Bio notes Respiration
P.7
ii) The final anaerobic pathway in animals
In animal cells the pyruvic acid is reduced
by the NADH, formed during glycolysis, to
lactic (2-hydroxypropanoic) acid.
This also regenerates the NAD+
(coenzyme for dehydrogenation) needed in
glycolysis.
i) The final anaerobic pathway in plants
In the absence of oxygen pyruvic acid is
converted to acetaldehyde (ethana1) and
carbon dioxide.
The NADH formed during glycolysis is
then used to reduce the acetaldehyde to
ethanol.
The oxidised NAD+ is then regenerated to
pick up more hydrogen atoms from
glycolysis.
b)
The Energy yield of Anaerobic respiration
The net yield from anaerobic respiration is thus 2 ATP per glucose molecule. Two moles of ATP
store about 66kJ. This is a small return from glucose, which stores about 2800 kJmol -1.
IV)
THE AEROBIC PATHWAY
If oxygen is available pyruvic acid enters mitochondria and there embarks on a series of reactions
that involves the removal of H atoms to the ETC--and the removal of CO2 molecules. The removal
of CO2 is always linked to a dehydrogenation and so is called oxidative decarboxylation.
Before entering the cycle, pyruvic acid (3C) is converted to acetyl coenzyme A (2C) (acetyl-CoA) by
oxidative decarboxylation. The Krebs cycle may be summarized into 4 major steps :
1. Formation of a 6-C citric acid molecule
Acetyl-CoA (2C) combines with oxaloacetic acid (4C), to form citric acid (6C).
2. Oxidation of the 6-C molecule
Citric acid (6C) is oxidized to -Ketoglutaric acid (5C) by oxidative decarboxylation.
3. Oxidation of the 5-C molecule
-Ketoglutaric acid is oxidized, to a 4-C intermediate by oxidative decarboxylation.
4. Oxidation and regeneration of Oxaloacetic acid
Further dehydrogenation occurs and oxaloacetic acid is regenerated. The cycle starts again with
another acetyl-CoA produced from pyruvic acid.
AL Bio notes Respiration
P.8
The Krebs or Tricarboxylic
acid cycle (TCA cycle)
Take place in the matrix of
mitochondria.
only operate if oxygen is
available to act as the final
electron acceptor.
6-carbon citric acid is
gradually broken down by
four dehydrogenations and
two decarboxylations to
reform the 4-carbon
oxaloacetic acid.
Taking into account the
oxidative decarboxylation
when pyruvic acid are
converted into acetyl CoA,
three CO2 molecules and 5
pairs of Hydrogens are
removed.
a)
The Energy yield of Aerobic respiration
5 pairs of H atoms are removed as pyruvic acid is broken down in the aerobic pathway, 4 pairs from
each turn of the Krebs cycle and one pair from the initial conversion of pyruvic acid into acetyl-CoA.
The total yield from this part of the respiratory process is thus ten pairs of hydrogen atoms per
glucose molecule (each glucose molecule is broken down to two molecules of pyruvic acid).
8 pairs are removed by NAD+, each pair providing sufficient energy to form 3 ATP molecules. The 2
pairs removed by FAD each provides enough energy to form 2 ATP molecules. To these must be
added the 2 pairs of hydrogen atoms removed during glycolysis. These are passed via a carrier/
shuttle in the mitochondrial membrane to either NAD+ or FAD within the mitochondria (varies
according to tissue type) resulting in the formation of either 6 or 4 ATP molecules. The total
number of ATP molecules formed by oxidative phosphorylation is thus :
(8 x 3) + (2 x 2) + 6 or 4 = 32 or 34.
To this must be added the 4 ATP molecules formed by substrate-linked phosphorylation ( 2 in
glycolysis, 2 in krebs cycle). The total yield from aerobic respiration is thus 36 or 38 molecules of
ATP per glucose molecule.
ATP yield during aerobic respiration of one molecule of glucose
Respiratory
process
No.of reduced
hydrogen carrier
molecules formed
No. of ATP molecules
formed from ETC
No. of ATP molecules from
substrate-level
phosphorylation
Total No.of
ATP
molecules
glucose to
pyruvate
(Glycolysis)
pyruvate to
acetyl CoA
Krebs (TCA)
cycle
Total ATP =
38
AL Bio notes Respiration
P.9
Q. Below is called Warburg apparatus which has been designed to measure the effect of various substances on the rate of
respiration.
Mung beans seeds were crushed with isotonic buffer enriched with glucose in cold.
Its extract was
made by a high speed differential centrifugation. The supernatant made by 1,000 g centrifugation was obtained and
used in this apparatus.
a) Why was it necessary to crush the seeds with isotonic buffer enriched with glucose in cold ?
(4m)
b) What essential component of the cell must be present in the extract? Why was it necessary?
(2m)
c) Why should the KOH be separated from the mung bean extract? What was the purpose of using the filter paper?
(2m)
d) After setting up the apparatus, its was left undisturbed. The manometric reading was recorded at one minute
intervals. At ten minutes, the Warburg apparatus was tilted slightly to mix the ADP from the side arm to the mung
bean extract. The result was recorded by graph I below.
i)
Explain the shape of graph I
I) before 10 minutes.
(2m)
II) after 10 minutes.
(2m)
ii) Identify two possible sources of errors which leaded to inaccuracy of the experiment.
which these errors could be minimized.
Suggest two ways in
(4m)
e) Another experiment was performed to demonstrate the effect of substance X on respiration. Substance X was
placed in the side arm of the Warburg apparatus instead of ADP. The same experiment was performed and
substance X was added to the extract at 20 minutes after commencement of the experiment. The result was
recorded in graph II above. Name a possible substance for 'X', explain how it might lead to the effect as shown in
graph II.
(4m)
AL Bio notes Respiration
b)
P.10
The Site of the Aerobic process
Mitochondria tend to be most abundant in cells with a high e________ requirement.
They are sausage-shaped organelles comprising two m_______ layers. Within the inner membrane
encloses an aqueous solution, the m______. The inner membrane is folded into c______ which project
into the matrix.
The matrix contains the en______ involved in the Krebs cycle and the breakdown of fatty acids,
while the inner mitochondrial membrane contains the en
and electron c
of the
electron transport chain (ETC).
There are tiny spheres on the inner membrane which are believed be the sites of ATP synthase, the
enzyme that brings about the formation of _____ from ADP and inorganic phosphate.. The cristae
presumably serve to increase the surface area for enzyme and carrier attachment.
Supporting this, it has been observed that the cristae are more numerous in cells with a high energy
requirement.
Draw an annotated diagram to show how the structure of a mitochondrion
is related to its function (5m)
AL Bio notes Respiration
V)
P.11
RESPIRATION USING OTHER SUBSTRATES
Carbohydrates are not the only
source of energy.
In certain circumstances, fats
and proteins can supply part of
the organism's energy needs.
The breakdown of fats and
proteins is largely dependent
on the presence of o_______
as they are converted into
substances, most of which
enter the Krebs cycle where
they are oxidised to yield their
energy.
a)
The use of fats as a respiratory substrate
Fats form the long-term energy stores in many organisms. They are generally used only when the
carbohydrate reserves are exhausted. Fats usually have a much higher energy yield than
carbohydrate. Some tissues like liver, and seeds possessing large deposits of fats and are able to use
fat directly as a respiratory substrate without first converting it to carbohydrate.
The fats are first removed from the fat depots (under the skin and around various internal organs), a
process known as mobilisation. They are then transported to the liver where they split into fatty acids
and glycerol.
The glycerol is phosphorylated to form triose phosphate / glyceraldehydes phosphate which enters
the glycolytic sequence.
Fatty acid molecules are oxidized by a process called β-oxidation, which involves 2C fragments of
acetyl CoA being split off from the acid until the entire fatty acid molecule has been broken up and
oxidised. This takes place in the matrix of the mitochondria.
Each acetyl CoA formed can enter the Krebs cycle. The longer the fatty acid chain, the greater will
be the energy yield. E.g 147 ATP can be obtained from one stearic acid molecules (C17H35COOH).
b)
Protein as a respiratory substrate
Many plant seeds employ protein as an energy storage material. Animals do not generally employ
protein as an energy reserve; they do so at the expense of their own tissue proteins. Accordingly,
proteins are only respired by animals as a last resort in cases of prolonged starvation.
When proteins are respired they are first broken down into amino acids. These are then deaminated,
that is, their nitrogen-containing amino group is removed. The products of deamination are ammonia
and an α-keto acid
AL Bio notes Respiration
P.12
Krebs cycle
CH3CH.NH2COOH
alanine
+
O2
CH3CO.COOH
pyruvic acid
+
NH3
ammonia
The ammonia is toxic and must be removed from the body. The residue (an α-keto acid) enters the
respiratory sequence.
VI)
SURVIVAL IN CONDITIONS OF OXYGEN SHORTAGE
The majority of organisms today are so dependent on the aerobic respiration that they will die if
deprived of oxygen for more than a few minutes. Such organisms are described as aerobes. At the
other extreme, some organisms depend entirely on anaerobic respiration. These organisms are called
anaerobes, and include many parasitic flatworms, as well as many of the bacteria that bring about
the decay of organic material. Both of these live in conditions where oxygen is not readily available.
Some anaerobes are actually poisoned by oxygen.
Certain organisms, notably yeast and some other fungi, are described as partial / facultative
anaerobes because, although they normally respire aerobically, they can respire anaerobically for
extended periods if oxygen is not available. It is sometimes mistakenly supposed that yeast can go
on respiring anaerobically indefinitely. This is not the case, yeast is unable to grow and reproduce
when respiring anaerobically, and the toxic alcoholic end-product of the process will kill the yeast if
it exceeds a certain concentration, usually about eighteen per cent.
Returning to aerobic organisms, while it is true that they are rapidly killed by total oxygen deprivation,
most have evolved mechanisms which enable them to survive periods of oxygen shortage. One such
adaptation is the possession of tissues which can respire anaerobically for limited periods. The
muscles of vertebrates provide an example of such a tissue. They can survive anaerobic conditions
for many minutes, much longer than, for example, brain cells which suffer irreparable damage if
deprived of oxygen for more than one or two minutes.
One value of this is that in conditions of oxygen shortage, blood can be diverted away from the
muscles to the tissues that need it most. This mechanism is particularly well developed in diving
animals such as the seal. During a dive, constriction of the blood vessels supplying the muscles cuts
off their blood supply and diverts blood (carrying oxygen) to the heart and brain. The muscles
respire anaerobically and the heart rate slows to accommodate the reduced circulation. In this way
these animals can remain submerged for up to twenty minutes without harm.
Human muscles 'switch over' to anaerobic respiration during strenuous activity, such as running,
when the circulatory system cannot supply oxygen to the muscles sufficiently quickly to supply their
energy needs. When the muscles respire anaerobically, lactic acid accumulates. The length of time
that the muscles can respire anaerobically is largely determined by their tolerance to lactic acid.
Regular exertion can build up tolerance to lactic acid.
The accumulation of lactic acid creates what is known as the oxygen debt. After the exercise, the lactic
acid is converted back to pyruvic acid and enters the aerobic pathway. The debt must then be
repaid, that is, extra oxygen must be taken in to complete the breakdown of the pyruvic acid
derived from lactic acid. This is usually achieved by panting rapidly in the period immediately after
the activity.
Some organisms vary their respiratory habits during their life history. For example, many plant seeds
respire anaerobically, and the pupal stages of certain insects enter an inactive stage (diapause)
during which they respire anaerobically.
AL Bio notes Respiration
Reference Exercise:
P.13
Exercise and training
Respiration is generally aerobic. Most muscle tissue, however, also respires anaerobically and produce
lactic acid (lactate) as waste products. Lactate is toxic if allowed to accumulate so, after a period of activity
has ended, it has to be converted back to glucose or changed to carbon dioxide in aerobic respiration.
Obviously, the amount of lactate that is formed during exercise determines the amount of oxygen needed
for its conversion after the exercise is over. This oxygen is referred to as the oxygen debt; there is a limit to the
oxygen debt which any individual can sustain.
Consider a male athlete. The amount of work that he can do in a given time will be determined largely by the
amount of oxygen that he can absorb in that time and the extent of the oxygen debt that he is able to
sustain.
If we assume that for every dm 3 of oxygen available to him, he can generate around 20 kJ, it is possible to
calculate how much energy he can make available for doing physical work. For example, suppose he can
absorb oxygen at a maximum rate of 2.5 dm 3 minute -1 and can sustain a maximum oxygen debt of 10 dm 3 over
a race lasting 3 minutes he can generate [(2.5 x 3) + 10] x 20 = 350kJ. Of course, his muscles are inefficient at
converting this into physical work and a figure of around 20 per cent is not unreasonable. So the individual in
our example could perform a maximum of 70 kJ of work.
When athletes compete, one of the major factors determining who wins is which of them has the largest
amount of oxygen available to him or her in terms of consumption and debt. Training must be designed
to increase the rate at which an individual can absorb oxygen, and it is this which is used as a measure of
physical fitness. (Of course, it is difficult to measure maximum oxygen consumption in field conditions, but
there is an almost linear relation between that and heart rate, so maximum heart rate is used instead.)
It should be remembered that not all tasks are equally dependent upon aerobic fitness. A trained sprinter, for
example, takes less than 10 seconds to run 100 metres. It has been calculated that this requires 6 dm3 of
oxygen, of which 0.5 dm 3 or less is inspired during the run, so that an oxygen debt of 5.5 dm 3 or more is built up.
So this activity is largely anaerobic and only around 8 per cent aerobic. Virtually all field events javelin, discus,
and the jumps are almost entirely anaerobic. A track event lasting a little longer than the sprint, such as a
400-metre race lasting 50 seconds, will be about 80 per cent anaerobic and 20 per cent aerobic and a
2000-metre rowing event lasting 6 minutes will be perhaps 55 per cent aerobic and only 45 per cent anaerobic.
This means that an athlete can be advised to choose an event to complement his or her own specific capacities
and, more important, to train appropriately for that event.
By training, an athlete can modify several other characteristics besides the one mentioned above. The
maximum oxygen debt that can be incurred by an untrained individual rarely exceeds 8 to 10 dm 3, but good
athletes can double this figure. Efficient use of the muscles is also improved by training and the cardiac
output (the volume of blood pumped per minute) can be greatly increased.
Measure
Heart rate at rest (beats minute -1)
3
Stroke volume at rest (cm )
3
Stroke volume, maximum (cm )
3
Heart volume (cm )
-1
Ventilation rate at rest (breaths minute )
Ventilation rate ( maximum breaths minute -1 )
3
Lung capacity (dm )
VO2 rest
3
-1
(cm kg
3
-1
minute -1 )
minute -1
VO2 max (cm kg
)
Lactate at rest (mg 100cm- 3)
Lactate, maximum
-3
(mg l00cm )
Pre-training
72
64
Post-training
58
79
International
36
128
120
140
200
750
820
1200
14
12
12
40
7.2
45
7.2
55
7.4
3.6
3.8
4.1
40
50
77
20
110
20
125
20
185
Summary of the changes taking place in a variety of cardiovascular and respiratory measures for a normal individual before
and as a result of training. The equivalent figures for an international athlete are also given. (VO 2 = oxygen uptake.)
a
From the data in the table calculate the cardiac output in dm 3 minute -1 of the three athletes at rest.
b
Which of the rows of data indicates most directly the athletes' ability to sustain oxygen debt ?
c
Describe the changes that have occurred to the heart as a result of the training in the international athlete compared
with the pre-training athlete.
AL Bio notes Respiration
d
P.14
There is a very big difference between the data for the normal individual after training and those for the international
athlete. Apart from the duration and extent of the training, what is the main factor determining the features such as
maximum cardiac output and maximum oxygen uptake ?
Oxygen debt
The second aspect of training concerns the most efficient use of the athlete's physical capabilities. A runner
who can maintain 85 per cent of a VO2max of 70cm3 kg-1 minute-1 will go faster than one who can only maintain
70 per cent of a higher consumption such as 80 cm 3 kg -1 minute -1. This may seem a small difference but
modern competitive sport is decided by much smaller percentage differences than this.
What happens if the first runner mentioned above runs at a higher rate of consumption than the 85 per cent
quoted? If, in practical terms, 85 per cent of the VO 2max is the maximum he or she can maintain for long periods,
then the runner has to obtain the additional energy from anaerobic sources. In other words, for this runner 59.5
cm3 kg-1minute' is the anaerobic threshold.
With training this threshold can be elevated to come closer and closer to the VO 2max. If the runner just dips into
anaerobic energy sources for a few seconds then there will probably be no apparent penalty; but if the
requirement is for more than six seconds or so then anaerobic respiration will be used in earnest and the
penalty will be the generation of lactic acid. Lactic acid is one of the main causes of fatigue when muscle is
forced to respire anaerobically.
a
What short-term beneficial effect will the athlete gain from the presence of lactic acid in the blood?
Obviously, training for a particular event, such as a 1500-metre track event, will have an important object
besides improving general fitness and increasing the capacities mentioned under 'Exercise and training'. It will
concentrate upon ensuring that the athlete does not arrive at his or her maximum oxygen debt before
reaching the winning tape. In any race, the maximum amount of energy that can be expended is given by the
maximum oxygen uptake for the duration of the race plus the athlete's maximum oxygen debt.
Suppose that an individual may incur an oxygen debt of 15 dm 3. To run at 8 metres per second he requires
oxygen at the rate of 0.2 dm 3 per second. His maximum rate of oxygen absorption is 4.0 dm 3 minute -1.
b
How far can he run at this speed before becoming completely exhausted?
c
What proportion of the energy that he has then used is associated with the oxygen debt ?
This amount of energy will need to be 'repaid' after
the race is finished.
Figure on the right represents the demand and
usage of oxygen by a runner during a short period
of vigorous running.
By the end of the race the subject was completely
exhausted and could run no further.
d
From the graph, what is the approximate value of
the
maximum oxygen debt substainable by this
athlete ?
3
3
3
A 12 dm
B 21 dm
C 33 dm
e
What is represented by the three areas, L, M, and N
on the graph ?
AL Bio notes Respiration
f
P.15
What is the maximum rate of oxygen consumption by this athlete ?
Two runners. A and B, can sustain maximum oxygen debts of 15 and 10dm 3 respectively. Additionally A has a
VO 2 max of 3 dm3 minute -1 and B has a VO 2max of 4 dm3 minute -1. The two runners are matched in two races.
One race is over 400 metres and takes about 50 seconds to complete; the other is over 5 kilometres and takes
about 14 minutes to complete. The runners are of the same mass and operate with the same muscular
efficiency.
g
VII)
Which runner will win each of these two races ?
MEASURING RESPIRATORY RATES
The rate of respiration is usually measured in terms of the amount of oxygen consumed or the
amount of carbon dioxide produced. The apparatus used to measure respiratory rates is called a
respirometer.
The respiring organisms are placed in
an airtight vessel and changes in gas
volume are measured at intervals.
If oxygen uptake is to be investigated,
sodium hydroxide is placed in the
apparatus to absorb carbon dioxide
and then any decrease in gas volume
can be attributed to oxygen
consumption by the respiring tissue.
The respiratory rate is generally taken
as a measure of the metabolic rate.
The two rates are approximately
equivalent, as all metabolic processes
require energy which is provided by
respiration.
What are the assumptions taken?
Suggest the necessary precautions for the experiment?
AL Bio notes Respiration
Common misconceptions
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Anaerobic respiration occurs in the absence of oxygen.
This is NOT the case for skeletal muscles, which carry out anaerobic respiration even when
oxygen is in abundance.
The significance of anaerobic respiration in the skeletal muscle is to provide additional energy to
the skeletal muscle so that it can contract more vigorously.
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Anaerobic respiration produces extra energy for muscle contraction because it can oxidise
food faster than aerobic respiration
In most cases, aerobic respiration is still a major source of energy for muscle contraction,
whereas anaerobic respiration supplies additional energy for promoting maximum exertion
It is only under very strenuous muscle activity taking place within a short period, e.g. in a 100m
sprint, that lactic acid fermentation will generate most of the energy required for muscle contraction.
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During exercise the muscle stops aerobic respiration but carries out anaerobic respiration as a
result of reduced oxygen supply.
In fact, the oxygen supply to the muscle is greatly increased during vigorous muscle contraction
so as to maintain a high rate of aerobic respiration. The onset of anaerobic respiration only serves to
provide an additional amount of energy for maximum exertion.
Also note that anaerobic respiration occurs only in the skeletal muscles, it does NOT take place in
all body cells during exercise.
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“During vigorous exercises, in spite of rapid breathing and strenuous pumping by the heart,
oxygen cannot reach the muscles fast enough to supply their needs. The muscles then switch
from aerobic respiration to anaerobic respiration, which does not use oxygen.”
A better statement should be “During exercise, the muscle cells are carrying out aerobic respiration
at a very high rate because of an increased oxygen supply from the blood, but anaerobic
respiration is also occurring simultaneously to provide additional energy for promoting maximum
exertion.”
Explanation for Fig 21: When the skeletal muscle is actively contracting, some glucose molecules
are broken down anaerobically into lactic acid (also a 3-carbon compound), while other glucose
molecules are broken down aerobically into carbon dioxide and water.
While aerobic respiration is occurring in full swing, anaerobic breakdown of glucose provides
additional amount of energy for muscular contraction. This additional amount of energy can be
very significant in urgent situations, such as when the animal is running away from a predator or
when the animal is chasing a prey.
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Sprints are purely anaerobic and marathons are purely aerobic activity.
Most physical exercises involve a mixture of BOTH aerobic and anaerobic muscular activities, but
they differ in the proportion of energy contribution from them.
P.16
AL Bio notes Respiration
19
Lactic acid is a wasteful by-product of anaerobic respiration to be removed by the liver
Lactic acid is an energy-rich by-product of anaerobic respiration in skeletal muscles, its value in
providing metabolic energy is recovered by the liver.
Anaerobic respiration in the skeletal muscle does not use oxygen. This process produces lactic acid
as a waste product. As lactic acid is toxic if allowed to accumulate in the blood, the body can only
carry out anaerobic respiration for a brief period of time, after which the lactic acid has to be
converted back to glucose or glycogen, or changed to carbon dioxide through aerobic
respiration.
In the liver, about 20% of the lactic acid in blood is broken down aerobically to produce a large amount
of ATP, which is used to convert the remaining 80% of lactic acid to glycogen. The oxygen
required to do this is called the oxygen debt. Thus all ATP molecules used by muscle cells come
ultimately from aerobic respiration. This explains why one needs to breathe deeply for some time at
the end of a sprint race.
Try the following questions to consolidate your understanding of oxygen debt:
20

What will happen if you lie down immediately after a 100-metre race?

If you are running a 1,600-rn race, what strategy will you use?

When should you carry out anaerobic respiration to secure maximum energy output for the
body?

What kind of training exercise will be useful for an athlete who is preparing for (i) a 100-rn race
and (ii) a marathon?
The oxygen content of atmospheric air and exhaled air can be compared by the glowing splint
test.
The glowing splint will be relighted only in the presence of high concentration of oxygen; it will NOT
work with normal atmospheric air or exhaled air.
A workable way is to compare the time of burning of a candle in the two air samples
The End
P.17