Student activity AB2.19.1
Lesson reference: B2.19 Energy and
life processes
Book links: Page 132
Specification links: B2.6.1 a–i;
B2.6.2 a–d
Energy and life processes
Equipment required per student/group:
Five test tubes
Test tube rack
Labels or marker pen
Tin foil
Drinking straw
10 cm3 measuring cylinder
2 cm3 syringe
50 cm3 hydrogencarbonate indicator solution
5 cm pondweed
Two water snails
2 cm3 yeast suspension
Stopwatch
Student book
Health and Safety notes:
 Make sure you blow and do not suck though the straw.
Getting started
1 Collect your apparatus and place the five test tubes in a rack. Label the test
tubes 1–5.
2 Place 10 cm3 hydrogencarbonate indicator solution into each test tube.
3 Apply the following treatment to the test tubes:
Tube 1 Use a drinking straw to blow expired air into the hydrogencarbonate
indicator solution. Notice how the colour changes as more of the
carbon dioxide from your exhaled air lowers the pH of the indicator
solution. Keep this tube.
Tube 2 Place a piece of pondweed into the hydrogencarbonate indicator
solution. Carefully wrap this tube in foil to exclude all light.
Tube 3 Place two water snails into the hydrogencarbonate indicator solution.
Tube 4 Place 2 cm3 yeast suspension into the hydrogencarbonate indicator
solution.
Tube 5 Leave one with no further treatment. This is the control.
4 Examine each of the test tubes after 5, 10, 15 and 20 minutes, and record the
colour of the hydrogencarbonate indicator solution.
5 While you are waiting, answer questions A–B and 1–6 on pages 132–133 of
the Student book.
Practical activities have been checked for health and safety advice by CLEAPSS.
All users will need to review the risk assessment information and may need to adapt it to local circumstances.
© Oxford University Press 2011
This document may have been altered from the original.
447
Asking questions
A Explain why breathing out into the indicator solution lowers the pH.
B Why do you think you were told to wrap the tube containing pondweed in foil?
C What life process is responsible for the change in colour of the indicator
solution in the test tubes?
D Explain why the control test tube was set up.
E What is the main limitation of this investigation in terms of the colour change in
the indicator solution?
F How do you think this investigation could be improved so that more
quantitative data could be obtained?
G What conclusions can you draw from this investigation?
H How could you improve the reliability of this investigation?
I How could you improve the validity of this investigation?
Spreading the word
How do you think you could use this apparatus to investigate how temperature
affects the rate of respiration in living organisms?
Think about the following questions:
 What apparatus would you need?
 Which living organisms would you use?
 What range of temperatures would you use?
 How would you make sure the data you collect are reliable?
 How would you make sure your investigation is valid?
 How would you present your data?
Practical activities have been checked for health and safety advice by CLEAPSS.
All users will need to review the risk assessment information and may need to adapt it to local circumstances.
© Oxford University Press 2011
This document may have been altered from the original.
448