Biology PAG 2: Testing for Biological Molecules
Suggested Activity 2: Testing for biological gases
Instructions and answers for teachers&
technicians
This practical activity is composed of two parts; a teacher/technician section and the learner activity
which can be found on page 10. This Practical activity supports OCR GCSE Biology.
When distributing the activity section to the learners either as a printed copy or as a Word
file you will need to remove the teacher instructions section.
This is a suggested practical activity that can be used as part of teaching the GCSE (9-1)
Gateway Science (A) and Twenty First Century Science (B) specifications.
These are not controlled assessment tasks, and there is no
requirement to use these particular activities.
You may modify these activities to suit your learners and centre. Alternative activities are
available from, for example, Royal Society of Biology, Royal Society of Chemistry, Institute of
Physics, CLEAPSS and publishing companies, or of your own devising.
Further details are available in the specifications (Practical Skills Topics), and in these videos.
OCR recommendations:
Before carrying out any experiment or demonstration based on this guidance, it is the
responsibility of teachers to ensure that they have undertaken a risk assessment in
accordance with their employer’s requirements, making use of up-to-date information and
taking account of their own particular circumstances. Any local rules or restrictions issued
by the employer must always be followed.
CLEAPSS resources are useful for carrying out risk-assessments:
(http://science.cleapss.org.uk).
Centres should trial experiments in advance of giving them to learners. Centres may choose
to make adaptations to this practical activity, but should be aware that this may affect the
Apparatus and Techniques covered by the learner.
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Introduction
In this activity learners will need to test two biologically important gasses: Oxygen (O2) and Carbon
dioxide (CO2).
Carbon dioxide is required by plants for photosynthesis and is produced by plants and animals
during respiration.
Oxygen is required by animals and plants for respiration and is produced by plants by
photosynthesis.
The tests for these gases are relatively simple and can be done by testing pure samples of the
gases in test tubes (for speed). Alternatively, the test can be part of a wider more applied practical
to prove which gas is produced by a biological change or process.
DfE Apparatus and Techniques covered
The codes used below match the OCR Practical Activity Learner Record Sheet (Biology /
Combined Science) and Trackers (Biology / Combined Science) available online. There is no
requirement to use these resources.
1 [1]: Use of appropriate apparatus to make and record a range of measurements accurately,
including length, area, mass, time, temperature, volume of liquids and gases, and pH.
3 [3]: Use of appropriate apparatus and techniques for the: i) observation of biological changes
and/or processes; ii) measurement of biological changes and/or processes
4 [4]: Safe and ethical use of living organisms (plants or animals) to measure physiological functions
and responses to the environment
5 [5]: Measurement of rates of reaction by a variety of methods including: iii) colour change of
indicator
8: Use of appropriate techniques and qualitative reagents to identify biological molecules and
processes in more complex and problem-solving contexts including: i) continuous sampling in an
investigation
Aims
To introduce learners to the tests for the gases oxygen and carbon dioxide.
Intended class time
If the quick experiment is chosen – 10 minutes
If the more detailed experiment is chosen – 20 minutes
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Links to Specifications:
Gateway
Describe some of the substances transported into and out of a range of organisms in terms of the
requirements of those organisms to include oxygen, carbon dioxide, water, dissolved food
molecules, mineral ions and urea.
Describe the process of photosynthesis to include reactants and products, two-stage process,
location of the reaction (in the chloroplasts).
Describe experiments that can be used to investigate enzymatic reactions.
Explain the mechanism of enzyme action to include the role of enzymes in metabolism, the role of
the active site, enzyme specificity (lock and key hypothesis) and factors affecting the rate of enzyme
controlled reactions (pH, temperature, substrate and enzyme concentration).
Compare the processes of aerobic respiration and anaerobic respiration to include in plants/fungi
and animals the different conditions, substrates, products and relative yields of ATP.
Twenty First Century
Compare the processes of aerobic and anaerobic respiration, including conditions under which they
occur, the inputs and outputs, and comparative yield of ATP.
Carry out rate calculations for chemical reactions in the context of cellular respiration.
Describe some of the substances transported into and out of the human body in terms of the
requirements of cells, including oxygen, carbon dioxide, water, dissolved food molecules and urea.
Describe some of the substances transported into and out of photosynthetic organisms in terms of
the requirements of those organisms, including oxygen, carbon dioxide, water and mineral ions.
Describe the process of photosynthesis, including the inputs and outputs of the two mains stages
and the requirement of light in the first stage, and describe photosynthesis as an endothermic
process.
Describe practical investigations into the requirements and products of photosynthesis.
Mathematical Skills covered
Use ratios, fractions and percentages
Understand and use the symbols: =, <, <<, >>, >, ∝, ~
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Gateway working scientifically references covered
Plan experiments or devise procedures to make observations, produce or characterise a substance,
test hypotheses, check data or explore phenomena.
Apply a knowledge of a range of techniques, instruments, apparatus, and materials to select those
appropriate to the experiment.
Evaluate methods and suggest possible improvements and further investigations.
Carry out experiments to include due regard to the correct manipulation of apparatus, the accuracy
of measurements and health and safety considerations, and following written instructions.
Make and record observations and measurements using a range of apparatus and methods to
include keeping appropriate records.
Presenting observations using appropriate methods to include methods to include descriptive,
tabular diagrammatic and graphically.
Communicating the scientific rationale for investigations, methods used, findings and reasoned
conclusions to include presentations through paper-based and electronic reports and presentations
using verbal, diagrammatic, graphical, numerical and symbolic forms.
Twenty First Century IaS references covered
Suggest appropriate apparatus, materials and techniques, justifying the choice with reference to the
precision, accuracy and validity of the data that will be collected.
Identify factors that need to be controlled, and the ways in which they could be controlled.
Suggest an appropriate sample size and/or range of values to be measured and justify the
suggestion.
Plan experiments or devise procedures by constructing clear and logically sequenced strategies to:
-
make observations
produce or characterise a substance
test hypotheses
collect and check data
explore phenomena.
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In a given context evaluate data in terms of accuracy, precision, repeatability and reproducibility,
identify potential sources of random and systematic error, and discuss the decision to discard or
retain an outlier.
Evaluate an experimental strategy, suggest improvements and explain why they would increase the
quality (accuracy, precision, repeatability and reproducibility) of the data collected, and suggest
further investigations.
In a given context interpret observations and other data (presented in diagrammatic, graphical,
symbolic or numerical form) to make inferences and to draw reasoned conclusions, using
appropriate scientific vocabulary and terminology to communicate the scientific rationale for findings
and conclusions.
Equipment (all equipment in this section is per group)
Quick activity
A stoppered test tube containing oxygen
Two stoppered test tubes containing carbon dioxide
A tube containing lime water
A tube containing bicarbonate indicator
A box of matches
Splints
Longer activity
Huff and puff apparatus
Lime water
Bicarbonate indicator
Follow the details available from the SAPS web site:
http://www.saps.org.uk/secondary/teaching-resources/190-using-pondweed-to-experiment-withphotosynthesis
Health and Safety
Teachers will need to carry out a suitable risk assessment for each practical. The following may
assist you in the preparation of your risk assessment:

Burn risk – matches and lit splints

Accidental ingestion of bicarbonate indicator or lime water

Cut hazard – broken glass
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Method
Quick activity
Test for carbon dioxide
Carbon dioxide is heavier than air so unstopping a test tube of CO2 will not lead to a rapid loss of
the gas. The gas could be poured onto a lit tea light / lit candle and the flame will be extinguished.
This test is not diagnostic as many gases can do this, but it is a good demonstration that the carbon
dioxide is heavier than air. Another good demonstration of the mass of carbon dioxide gas is a
balloon of pure CO2 is notably heavier than a control balloon containing exhaled air.
With the following tests a control tube of air could be used.
Pour 5 cm3 of lime water into the tube containing the carbon dioxide re-stopper the tube then shake.
A positive result for carbon dioxide is the lime water turning milky white.
The lime water – a solution of calcium hydroxide reacts with the carbon dioxide to produce calcium
carbonate (solid) and water.
Ca(OH)2 (aq) + CO2 (g)  CaCO3 (s) + H2O (l)
Alternative test
Pour 5 cm3 of bicarbonate indicator into the tube containing the carbon dioxide re-stopper the tube
then shake. Carbon dioxide will turn the bicarbonate indicator yellow.
This is because the Carbon dioxide reacts with the water of the indicator solution and will produce
carbonic acid.
CO2 + H2O  H2CO3
Bicarbonate indicator turns yellow in the presence of an acid.
Get the learners to realise that all of the tests above will lead to the conclusion that the gas is carbon
dioxide.
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Test for oxygen
Oxygen will relight a glowing splint. So light a splint, allow the flame to burn for a while then blow
out the flame. Adding the glowing splint into the pure oxygen will result in the flame being rekindled.
This can be done a number of times with the same test tube of oxygen.
Longer activity
Test for carbon dioxide
Use the huff and puff apparatus to breathe normally and to show that the exhaled gas contains
carbon dioxide whereas the inhaled gas does not contain as much carbon dioxide. Both lime water
and bicarbonate indicator can be used in this experiment.
Test for oxygen
Follow the instructions found on: http://www.saps.org.uk/secondary/teaching-resources/190-usingpondweed-to-experiment-with-photosynthesis
Test the gas produced as indicated above.
Having tried this experiment a number of times it is evident that the gas produced can occasionally
not relight the glowing splint. It may, therefore, be prudent to have a mock experiment containing a
tube of pure oxygen from a cylinder available should the test not provide enough collected gas.
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Technician Notes
For this practical the teacher will require for a class of 30:
Quick activity

15 stoppered test tubes containing oxygen [if an oxygen cylinder is not available then oxygen
can be produced by the decomposition of H2O2 using a suitable catalyst manganese (IV)
oxide. Collecting the gas over water]

31 stoppered test tubes containing carbon dioxide [if a carbon dioxide cylinder is unavailable
then carbon dioxide can be made by reacting a suitable carbonate (e.g. marble chips) with
acid as carbon dioxide is heavier than air then the gas can be collected into a dry tube]

Boxes of matches

1 tea light candle

Splints

Sufficient bottles / test tubes of lime water (a total of 500 cm3 should be enough)

Sufficient bottles / test tubes of bicarbonate indicator (a total of 500 cm3 should be enough)
Longer activity

15 huff and puff apparatuses

Bottles of lime water and/or bicarbonate indicator enough to fill the huff and puff apparatuses
(a total of 750 cm3 should be sufficient)

Boxes of matches

1 tea light candle

Splints

Equipment as specified in http://www.saps.org.uk/secondary/teaching-resources/190-usingpondweed-to-experiment-with-photosynthesis.
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Answers for quiz questions
1.
How would you test whether an unknown gas is oxygen? [1 mark]
A
Burns with a squeaky pop
B
Extinguishes a flame
C
Turns lime water milky white
D
Relights a glowing splint
Your answer
2.
D
How would you test whether an unknown gas is carbon dioxide? [1 mark]
A
Burns with a squeaky pop
B
Extinguishes a flame
C
Turns lime water milky white
D
Relights a glowing splint
Your answer
C
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Biology PAG 2: Testing for Biological Molecules
Suggested Activity 2: Testing for biological gases
Learner Activity
Introduction
In this activity you will need to test two biologically important gasses: Oxygen (O2) and Carbon
dioxide (CO2).
Carbon dioxide is required by plants for photosynthesis and is produced by plants and animals
during respiration.
Oxygen is required by animals and plants for respiration and is produced by plants by
photosynthesis.
The tests for these gases are relatively simple and can be done by testing pure samples of the
gases in test tubes (for speed). Alternatively, the test can be part of a wider more applied practical
to prove which gas is produced by a biological change or process.
Aims
To learn the tests for the gases oxygen and carbon dioxide.
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Method
Test for carbon dioxide
Carbon dioxide is heavier than air so unstopping a test tube of CO2 will not lead to a rapid loss of
the gas. The gas could be poured onto a lit tea light / lit candle and the flame will be extinguished.
This test is not diagnostic as many gases can do this, but it is a good demonstration that the
carbon dioxide is heavier than air and can be poured. Another good demonstration of the mass of
carbon dioxide gas is comparing the mass of a balloon of pure CO2 to a control balloon containing
exhaled air.
With the following tests a control tube of air could be used.
Pour 5 cm3 of lime water into the tube containing the carbon dioxide re-stopper the tube then
shake. A positive result for carbon dioxide is the lime water turning milky white.
Alternative test
Pour 5 cm3 of bicarbonate indicator into the tube containing the carbon dioxide re-stopper the tube
then shake. Carbon dioxide will turn the bicarbonate indicator yellow.
Bicarbonate indicator turns yellow in the presence of an acid.
Get the learners to realise that all of the tests above will lead to the conclusion that the gas is
carbon dioxide.
Test for oxygen
Oxygen will relight a glowing splint. So light a splint, allow the flame to burn for a while then blow
out the flame. Adding the glowing splint into the pure oxygen will result in the flame being
rekindled. This can be done a number of times with the same test tube of oxygen.
Longer activity
Test for carbon dioxide
The huff and puff apparatus can be used to investigate the composition of exhaled gas compared
to inhaled gas. You may use lime water and or bicarbonate indicator in this experiment.
Test for oxygen
Follow the instructions found on: http://www.saps.org.uk/secondary/teaching-resources/190-usingpondweed-to-experiment-with-photosynthesis
Test the gas produced as indicated above.
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Health and Safety
Take care when using naked flames.
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Quiz questions
1.
How would you test whether an unknown gas is oxygen? [1 mark]
A
Burns with a squeaky pop
B
Extinguishes a flame
C
Turns lime water milky white
D
Relights a glowing splint
Your answer
2.
How would you test whether an unknown gas is carbon dioxide? [1 mark]
A
Burns with a squeaky pop
B
Extinguishes a flame
C
Turns lime water milky white
D
Relights a glowing splint
Your answer
DfE Apparatus and Techniques covered
If you are using the OCR Practical Activity Learner Record Sheet (Biology / Combined Science) you
may be able to tick off the following skills:
1-vii
4-ii
Biology
3-i
3-ii
5-i
5-iii
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4-i
8-i
1-vii
4-ii
13
Combined Science
3-i
3-ii
5-i
5-iii
4-i
8-i
© OCR 2017