1. 2.8 Cell Respiration
Essential idea: Cell respiration supplies energy for the functions of life.
Energy in cells is all about the molecule shown, Adenosine Triphosphate (ATP). The energy is held in the bonds between atoms, in particular the high energy bond that joins the second and third phosphates. ATP is the energy currency of the cell. Hence the efficiency of respiration is measured by the yield of ATP.
By Chris Paine

2. Understandings, Applications and Skills
Statement
Guidance
2.8.U1
Cell respiration is the controlled release of energy from organic compounds to produce ATP.
Details of the metabolic pathways of cell respiration are not needed but the substrates and final waste products should be known.
2.8.U2
ATP from cell respiration is immediately available as a source of energy in the cell.
2.8.U3
Anaerobic cell respiration gives a small yield of ATP from glucose.
2.8.U4
Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
2.8.A1
Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
2.8.A2
Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
2.8.S1
Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to temperature fluctuations.

3. 2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

4. 2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

5. 2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

6. 2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

7. 2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.

8. 2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.

9. 2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.

10. 2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell.
All processes release heat energy and hence all energy eventually ends up as heat.
The heat energy initially can be used to raise the temperature of the organism, …
… but eventually it is lost to the environment and cannot be used for metabolic processes.

11. This links to 2.5 Enzymes and 8.1 Metabolism (AHL)
2.8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
This links to 2.5 Enzymes and 8.1 Metabolism (AHL)

12. 2.8.U4 Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.

13. 2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.

14. 2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Can you describe how the respirometer works and the function of each part of the apparatus?

15. Potassium hydroxide (alkali) solution
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Aerobic respiration uses 6 molecules of gas (oxygen) and creates 6 molecules of gas (carbon dioxide) = no change in volume, but …
Filter paper wicks
Increase the efficiency of carbon dioxide absorption
… carbon dioxide is absorbed therefore the volume of gas in the respirometer decreases.
Respiring organism
Suitable living organism will respire aerobically
Potassium hydroxide (alkali) solution
Hydroxide solutions are used to absorb carbon dioxide in the air

16. Capillary tube containing coloured oil
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Syringe
Used to reset the position of the coloured oil
Capillary tube containing coloured oil
Movement in the oil per minute toward tube B measures the rate of oxygen consumption. If the diameter of the capillary tube is known then a volume can be calculated
Rubber bungs seal tubes
Closes the system to prevent changes in air volume not due to respiration
Metal cage
Keeps the organism in place and away from contact with the hydroxide solution.

17. Temperature controlled
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Hoffman clip
Seals the respirometer and can be opened to reset it after the volume has been reduced by oxygen consumption.
Temperature controlled
The respirometer is immersed in a water bath to prevent temperature affecting the pressure and hence volume of air in the apparatus.
n.b. due to gas expansion the Hoffman clip should be left open until the respirometer is at the desired temperature – if not an explosion can result.

18. 2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Tube A
Acts as a control to ensure that changes in the level of coloured oil are due to respiration, not the reaction of the akali with atmospheric gases other than carbon dioxide.

19. Nature of Science: assessing the ethics of scientific research - the use of invertebrates in respirometer experiments has ethical implications. (4.5)
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Respiring organism: If using invertebrates rather than seeds what are the ethical questions that need answering?

20. Can the animals be safely returned to their habitat?
Nature of Science: assessing the ethics of scientific research - the use of invertebrates in respirometer experiments has ethical implications. (4.5)
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
Respiring organism: If using invertebrates rather than seeds what are the ethical questions that need answering?
Is it acceptable to remove animals from their natural habitat for use in an experiment?
Can the animals be safely returned to their habitat?
Will the animals suffer pain or any other harm during the experiment?
Can the risk of accidents that cause pain or suffering to the animals be minimized during the experiment? In particular, can contact with the alkali be prevented?
Is the use of animals in the experiment essential or is there an alternative method that avoids using animals?

21. You should aim to carry out your own investigation
2.8.S1 Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
The diagram shows the design of a typical respirometer. They vary greatly in their design, but all can be used to calculate the rate of respiration by measuring the consumption of oxygen.
You should aim to carry out your own investigation
In the absence of equipment you can use the worksheet (Q1-10) with the virtual lab:

22. 2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

23. 2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.

24. 2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
Bread is made by adding water to flour, kneading the mixture to make dough and then baking it. Usually an ingredient is added to the dough to create bubbles of gas, so that the baked bread has a lighter texture (e.g. yeast).
After kneading (mixing) the dough is kept warm to encourage the yeast to respire.
Yeast can respire aerobically or anaerobically, but oxygen in the dough is soon used up so the yeast is forced to respire anaerobically.
The carbon dioxide produced by anaerobic cell respiration cannot escape from the dough and forms bubbles causing the dough to swell and rise.
Ethanol is also produced by anaerobic cell respiration, but it evaporates during baking.

25. 2.8.A1 Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
Bioethanol (ethanol produced by organisms) is a renewable energy source.
Most bioethanol is produced from sugar cane and maize, using yeast.
Starch and cellulose in the plant material are broken down by enzymes into sugars.
Fermenters are used to keep the yeast in optimum conditions.
When yeast carry out anaerobic respiration the sugars in the plant material are converted to ethanol and carbon dioxide.
The ethanol produced by the yeasts is purified by distillation and water is removed to improve combustion.

26. 2.8.A2 Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
Certain human activities require anaerobic respiration such as weightlifting and sprinting.
Aerobic respiration generates a much greater yield of ATP, but anaerobic respiration can supply ATP very rapidly, as oxygen is not required.
Rapid generation of ATP enables us to maximise the power of muscle contractions.
Anaerobic cell respiration produces lactate. There is a limit to the concentration that the body can tolerate and this limits how much or how long anaerobic respiration can be done for.
Afterwards lactate must be broken down. This involves the use of oxygen. It can take several minutes for enough oxygen to be absorbed for all lactate to be broken down. The demand for oxygen that builds up during a period of anaerobic respiration is called the oxygen debt.

27. Bibliography / Acknowledgments
Jason de Nys