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Lesson Element
Unit 1: Science fundamentals
LO4: Understand the principles of carbon
chemistry
The role of carbohydrates in respiration
Instructions and answers for tutors
These instructions cover the learner activity section which can be found on page 7. This
Lesson Element supports Cambridge Technicals Level 3 in Laboratory Skills.
When distributing the activity section to the learners either as a printed copy or as a
Word file you will need to remove the tutor instructions section.
The activity
In this activity the learners are expected to work in groups to develop an understanding of
the role organic chemistry plays in biological systems through consideration of respiration,
both aerobic and anaerobic. They will be expected to research terminology, reactions and
real world examples of the respiratory processes. Wherever possible, learners should have
access to the internet and be encouraged to obtain a wide range of evidence to support their
findings. The group discussion, which is the final activity, may raise a number of issues not
least the poor quality and accuracy of some of the sources they have found as well as
excellent examples of respiration.
The tutor is a facilitator, guiding the learners in terms of research, identifying the important
and relevant points and producing a lucid argument. In the final activity the tutor will lead the
discussion so ensure that learners complete the activity with a good understanding of the
role of carbohydrates in the chemical reactions which occur during respiration.
This activity could also contribute to the learners’ understanding of the role of organelles,
covered in Learning Outcome 3.
ABC – This activity offers an
opportunity for English skills
development.
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WORK – This activity offers
an opportunity for work
experience.
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Suggested timings
Activity 1: 30 minutes
Activity 2: 1 hour
Activity 1
You should ask the learners to form groups of two to four and research the correct definition
for each of the terms in the table: they are all are linked with respiration. The following links
may stimulate the learners’ research.
An explanation of respiration:
http://www.rsc.org/Education/Teachers/Resources/cfb/respiration.htm
A lighthearted view of the Krebs cycle:
https://www.youtube.com/watch?v=JPCs5pn7UNI
Answers
Term
Respiration
Aerobic respiration
Anaerobic respiration
Definition
The chemical process by which organic compounds release
energy.
Respiration which requires the presence of oxygen, that is to
say, Glucose + oxygen  Carbon dioxide + water + energy
Respiration which does not require the presence of oxygen.
Plants and fungi:
Glucose  ethanol + carbon dioxide + energy
Glycolysis
Respiratory substrate
Respiratory quotient
(RQ)
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Animals:
Glucose  lactic acid + energy
A series of chemical reactions which break down the glucose
molecule C6H12O6 into two pyruvate molecules. The formula for
pyruvate is C3H4O3. It does not require oxygen and does not
release carbon dioxide; it does produce sufficient energy to
make two ATP molecules per glucose molecule.
Any chemical compound which can be broken down during
respiration to release energy.
This is equal to the amount of carbon dioxide produced divided
by the amount of oxygen produced. For a carbohydrate RQ is 1
during aerobic respiration. In anaerobic respiration, only carbon
dioxide is produced and no oxygen used and so, if the two are
occurring together, then the RQ may rise above 1.
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Term
ATP
ADP
Oxygen debt
Exergonic reaction
Definition
Adenosine triphosphate is the chemical substance which is
created during respiration from ADP (adenosine diphosphate)
and P (phosphate). It is the energy supply for all cell processes
which require it. Often known as the ATP/ADP cycle, the
formulae are:
When energy is available
ADP + P + Energy  ATP
and when the energy has been used
ATP  ADP + P + Energy.
Adenosine diphosphate
The amount of oxygen, which needs to be inhaled after
exercise, in order to oxidise the lactic acid that has
accumulated during exercise which has resulted in anaerobic
respiration
Energy is released to the surroundings. The bonds being
formed are stronger than the bonds being broken.
Activity 2
You should arrange the learners into small groups and provide them with access to
resources about the Krebs cycle; some are provided in the resource list above.
In the previous activity the learners will have identified and explained glycolysis and the next
stage of the process of aerobic respiration, that is to say the creation of two pyruvate
molecules from one glucose molecule.
The next stage of aerobic respiration is the Krebs cycle. In their groups, learners should
research the Krebs cycle and identify the alternative names by which it is known.
Alternative names for the Krebs cycle are:
 Tricarboxylic acid cycle often abbreviated to TCA cycle
 Citric acid cycle.
Learners should be told to put together a presentation on the Krebs cycle using any
appropriate resources they can find. In the presentation they are required do the following:
Explain:
1.
The link between glycolysis and the Krebs cycle
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2.
Conversion of pyruvate to acetyl CoA and the creation of two (nicotinamide adenine
dinucleotide) NADH c-enzymes and two CO2 molecules released.
3.
The location, within a cell, where the Krebs cycle is carried out.
4.
The mitochondria
5.
The specific areas of the Krebs cycle identified in the diagram below.
Answers to 5:
A: Citrate
Oxaloacetate and acetyl-CoA bind to the enzyme, citrate synthase, which then catalyses or
causes the reaction which joins the two compounds together. This results in the joining of
acetyl group CH3COO transferring from the COA to the oxaloacetic acid, which has four
carbon atoms, to form the six carbon atom citrate.
B: Isocitrate
There are two steps to isomerising the –OH group on citric acid. Firstly, through dehydration
of an alcohol, an alkene is created. The cis-aconitic acid is not released from the bond with
aconitase but instead the next reaction, hydration, is carried out to make alcohol. Thus
moving the –OH from C3 in citric acid to C2 in isocitrate
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C: α-ketoglutarate
To create α-ketoglutarate from isocitrate is a two-step reaction. In the first reaction, NADH is
generated from NAD for the first time in this cycle. The enzyme isocitrate dehydrogenase is
the catalyst for the oxidation of the –OH group at C4 of isocitrate to create an intermediate
and then generate NADH from NAD. The second reaction results in the removal of a carbon
dioxide molecule from the intermediate to yield α-ketoglutarate
D: Succinyl CoA
α-ketoglutarate, in a reaction catalysed by α-ketoglutarate dehydrogenase, loses a carbon
dioxide molecule and coenzyme A is added in its place. The removal of the carbon dioxide
molecule occurs with the help of NAD, which is converted to NADH. The resulting molecule
is called succinyl-CoA.
E: Succinate
The enzyme succinyl-CoA now catalyses a reaction in which a molecule of guanosine
triphosphate (GTP) or ATP is synthesised. A phosphate group is substituted for coenzyme A
and thus a high energy bond is formed. This energy is used in the phosphorylation of ADP or
GDP to synthesise either ATP or GTP respectively. The remaining molecule is succinate.
The decision on whether the synthesis of GTP or ATP is dependent upon the needs of
individual tissue types. Those which use large amounts of ATP are tissues such as the heart
or the muscles whereas tissue such as the liver uses large amounts of GTP. This is possible
because the enzyme can take one of two isomeric forms.
F: Fumarate
Succinate is converted into fumarate by transferring two hydrogen atoms to FAD, producing
FADH2 and dehydrating succinate to form fumarate. The energy contained in the electrons
of these atoms is insufficient to reduce NAD+ but adequate to reduce FAD. Unlike NADH,
this carrier remains attached to the enzyme and transfers the electrons to the electron
transport chain directly. This process is made possible by the fact that the enzyme which
catalyses this step is located inside the inner membrane of the mitochondrion.
G: Malate
Fumarate is converted to malate by the hydration of the double carbon bond of fumarate to
produce L-malate.
H: Oxaloacetate
This is the last reaction of the Krebs cycle. L-malate dehydrogenase linked to NAD+ is the
catalyst which removes a water molecule from L-malate to form Oxaloacetate and NADH +
H+.
If you have several groups you could ask the learners to concentrate on a subset of the
areas listed above.
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The presentations could be limited in time; 10 minutes is suggested.
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OCR Resources: the small print
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board,
and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for
any errors or omissions within these resources.
© OCR 2015 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the
originator of this work.
OCR acknowledges the use of the following content: Citric Acid Cycle diagram, www.shutterstock.com
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Lesson Element
Unit 1: Science fundamentals
LO4: Understand the principles of carbon
chemistry
Learner Activity
The role of carbohydrates in respiration
You will work with a small group to explain the role of organic chemistry in respiration. To do
this you will be required to carry out a number of activities which will not only help you to
understand the processes and steps in respiration but also improve your ability to research
and investigate problems, record your findings and present a clear and accurate explanation
to other people and defend your ideas in discussion. These are all important skills for
scientists and science technicians. Your understanding of the terminology, reactions and
outcomes will strengthen your understanding of formulae, ions and the role of organelles in
biological systems.
Activity 1
The table overleaf contains the main terms involved in respiration. You are required to
provide a definition of each term.
The following links may be of initial help in your research:
http://www.rsc.org/Education/Teachers/Resources/cfb/respiration.htm
https://www.youtube.com/watch?v=JPCs5pn7UNI
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Term
Definition
Respiration
Aerobic respiration
Anaerobic respiration
Glycolysis
Respiratory substrate
Respiratory quotient (RQ)
ATP
ADP
Oxygen debt
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Activity 2
The next stage of aerobic respiration is the Krebs cycle. In your group, you should research
the Krebs cycle and identify the alternative names by which it is known.
Alternative names for the Krebs cycle are:
You should then put together a presentation on the Krebs cycle, using any appropriate
resources you can find. In the presentation you must include the following:
Explain:
1.
The link between glycolysis and the Krebs cycle.
2.
The location within the cell where the Krebs cycle occurs.
3.
The specific areas of the Krebs cycle identified in the green circles in the diagram below:
for example citrate.
Your presentation should take no more than 10 minutes.
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