Revision Notes

12.2 Aerobic Respiration

Aerobic Respiration: Basics

  • Aerobic respiration requires oxygen and is defined as the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
  • It is the complete breakdown of glucose to release a relatively large amount of energy for use in cell processes
  • It produces carbon dioxide and water as well as releasing useful cellular energy


Word equation for aerobic respiration, IGCSE & GCSE Chemistry revision notesWord equation for aerobic respiration

Exam Tip

Remember this equation is the same as the photosynthesis equation, only the other way around, so if you know one, you know the other one too!

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Aerobic Respiration Balanced Equation

Balanced equation for aerobic respiration, IGCSE & GCSE Chemistry revision notes

Balanced equation for aerobic respiration


Exam Tip

There are usually 3 marks given for the aerobic respiration chemical equation in an exam:

  • one for getting the correct formula for glucose and oxygen
  • one for getting the correct formula for carbon dioxide and water
  • one for balancing the equation correctly

So make sure you can do all three to gain maximum marks!

Investigating Uptake of Oxygen by Respiring Organisms

  • We can investigate aerobic respiration in living organisms by measuring the amount of oxygen that they take from the air
  • This is done by measuring the change in volume in an enclosed tube containing the organisms
  • However, as they respire the organisms release carbon dioxide, which increases the gas volume
  • The carbon dioxide must therefore be removed from the tube using a chemical like soda lime or sodium hydroxide, otherwise it will make the experiment results inaccurate
  • Any small organisms can be used in the apparatus, including seeds or arthropods
  • The apparatus (shown below) is known as a respirometer


Investigating respiration using a respirometer, IGCSE & GCSE Chemistry revision notesDiagram showing the setup of a respirometer


  • The apparatus consists of two tubes, one containing the living organisms and the other with glass beads to act as a control
  • Once the apparatus has been set up, the movement of the coloured liquid towards the insect will give a measure of the volume of oxygen taken up by the insect for respiration
  • The reduction of volume in the tube increases pressure causing the coloured liquid to move
  • The distance moved by the liquid in a given time is measured will provide the volume of oxygen taken in by the insect per minute

Exam Tip

What is a control?

A control is a duplicate experiment set up with the condition being investigated having been removed or neutralised in some way.

In the experiment above, the control is the glass beads.

As they are not alive, they will definitely not be respiring. If the volume of oxygen decreases in the tube with the glass beads during the course of the experiment, then we know that the condition being investigated (respiration in living organisms) is not the cause of it.

So, a control helps to make your experiment valid.

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Investigating the Effect of Temperature on the Rate of Respiration

  • To investigate the effect of temperature on the rate of respiration of germinating seeds the respirometer can be set up and the tubes submerged in a series of water baths set at different temperatures, eg 10℃, 15℃, 20℃, 25℃, 30°C
  • The seeds should be kept in the water bath for 15 minutes before the start of the experiment to ensure they have acclimated to the temperature
  • As respiration is an enzyme controlled reaction, it is unlikely to work faster beyond around 40℃ as the enzymes will denature

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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