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 Applied Science.

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 activityIn 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.

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WORK – This activity offers an opportunity for work experience.

ABC – This activity offers an opportunity for English skills development.

Suggested timingsActivity 1: 30 minutes

Activity 2: 1 hour

Activity 1You 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 DefinitionRespiration The chemical process by which organic compounds release

energy. Aerobic respiration Respiration which requires the presence of oxygen, that is to

say, Glucose + oxygen Carbon dioxide + water + energyAnaerobic respiration Respiration which does not require the presence of oxygen.

Plants and fungi:Glucose ethanol + carbon dioxide + energy

Animals:Glucose lactic acid + energy

Glycolysis 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.

Respiratory substrate Any chemical compound which can be broken down during respiration to release energy.

Respiratory quotient (RQ)

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 DefinitionATP 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 usedATP ADP + P + Energy.

ADP Adenosine diphosphateOxygen debt 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

Exergonic reaction Energy is released to the surroundings. The bonds being formed are stronger than the bonds being broken.

Activity 2You 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

2. Conversion of pyruvate to acetyl CoA and the creation of two (nicotinamide adenine dinucleotide) NADH c-enzymes and two CO2 molecules released.

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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: IsocitrateThere 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

C: α-ketoglutarateTo 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

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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 CoAα-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: SuccinateThe 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: FumarateSuccinate 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: MalateFumarate is converted to malate by the hydration of the double carbon bond of fumarate to produce L-malate.

H: OxaloacetateThis 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.

The presentations could be limited in time; 10 minutes is suggested.

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Lesson Element

Unit 1: Science fundamentals

LO4: Understand the principles of carbon chemistry

Learner ActivityThe role of carbohydrates in respirationYou 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 1The 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 2The 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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