Respiration 2.8

Respiration is one of the seven characteristics of all living things and it is essential for life. This topic covers the basics of aerobic and anaerobic respiration. It is important to know what the role of ATP is in cells and also to have experience of using a respirometer to measure the rate of respiration.

Key words

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Revision summary list for topic 2.8 Respiration

  • Cell respiration definition,"the controlled release of energy from organic compounds to produce ATP"
  • ATP produced is a source of energy ready for immediate use in the cell.
  • Anaerobic cell respiration gives a small yield of ATP from glucose compared to aerobic respiration whose yield is large.
  • Aerobic cell respiration also requires oxygen.
  • Substrates (e.g. glucose) and final waste products (e.g. water, CO2, lactate, ethanol) should be known.
  • Anaerobic cell respiration in yeasts is used to produce ethanol and carbon dioxide in baking.
  • In the human body anaerobic respiration is used to maximize the power of muscle contractions & produces lactate.
  • Know how to use simple respirometers to measure the rate of respiration.
    • to know that an alkali is used to absorb CO2 produced in respirometers, so that reductions in gas volume are due to oxygen use.
    • To keep the temperature constant, so that gas volumes don't change through expansion / contraction of gas.

Revision mind map

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Review questions

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Which of the following is the best definition of 'cell respiration'?

The best answer is the controlled release of energy etc. because it also includes ATP and it does not limit the process to glucose.

Ventilation of the lungs / breathing is not ''cell respiration", but you knew that didn't you?


How much ATP is produced in anaerobic respiration compared to aerobic respiration?

The high yield of ATP is one of the key features of aerobic respiration.

Aerobic respiration produces more than 10 times the ATP of anaerobic respiration.


Aerobic and anaerobic bacteria can be identified by growing them in a liquid nutrient medium.

In these diagrams of three test tubes there are:

  • bacteria which need oxygen to survive ,
  • bacteria which can only survive in the absence of oxygen and
  • bacteria which can survive with or without oxygen.

Which of the following is the best explanation why the bacteria are more dense near the surface of test tubes 1 & 3?

Aerobic respiration produces lots more ATP than anaerobic respiration so bacteria with access to oxygen will have more ATP (energy) and be able to grow more quickly.
In tube 2 the bacteria cannot survive in the presence of oxygen and so cannot benefit from aerobic respiration. Those in 1 & 3 can use oxygen.

In an experiment to measure the rate of respiration shown below, some peas were placed into a test tube

What is the role of potassium hydroxide?

Carbon dioxide can be absorbed by an alkali. Sodium hydroxide, or potassium hydroxide are often used.


In this experiment to measure the rate of respiration, shown below, peas were left in the equipment for two hours. The temperature was controlled, and kept at 25°C.

Which direction would you expect to see the bubble in the capillary tube to move during the experiment?

Respiration will be happening in the germinating peas and they will be respiring at a fast enough rate to move the bubble in the capillary tube.

The absorbent cotton will absorb the carbon dioxide produced by respiration and oxygen will be absorbed by the peas. Tis causes the bubble to move towards the peas.


Muscle contraction require a lot of energy during strenuous exercise.

The graph below shows blood lactate levels at increasing power outputs while cycling.

Sometime the effort uses more energy than can be provided by aerobic respiration alone.

Which of the following statements best describes what is happening at the points A to d on the graph?

Muscle cells will use anaerobic and aerobic respiration at the same time when undergoing strenuous exercise. They do aerobic respiration at lower power outputs and increasing amounts of anaerobic respiration as the output increases.


In humans what is the purpose of making lactate from pyruvate during anaerobic respiration?

Anaerobic respiration in human produces lactate (sometimes called lactic acid)

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