CIE IGCSE Biology

Revision Notes

11.4 Exercise & Breathing

Investigating the Effect of Exercise on Breathing

  • Exercise increases the frequency and depth of breathing
  • This can be investigated by counting the breaths taken during one minute at rest and measuring average chest expansion over 5 breaths using a tape measure held around the chest
  • Exercise for a set time (at least 3 minutes)
  • Immediately after exercising, count the breaths taken in one minute and measure the average chest expansion over 5 breaths
  • Following exercise, the number of breaths per minute will have increased and the chest expansion will also have increased
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Explaining the Effect of Exercise on Breathing

  • Frequency and depth of breathing increase when exercising
  • This is because muscles are working harder and aerobically respiring more and they need more oxygen to be delivered to them (and carbon dioxide removed) to keep up with the energy demand
  • If they cannot meet the energy demand they will also respire anaerobically, producing lactic acid
  • After exercise has finished, the lactic acid that has built up in muscles needs to be removed as it lowers the pH of cells and can denature enzymes catalysing cell reactions
  • It can only be removed by combining it with oxygen – this is known as ‘repaying the oxygen debt’
  • This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal – the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid
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Carbon Dioxide Concentration & the Brain

  • As respiration rates increase, more carbon dioxide is produced and enters the blood
  • Carbon dioxide is an acidic gas in solution and so it can affect the working of enzymes in the cells and needs to be removed as quickly as possible
  • As blood flows through the brain, the increase in carbon dioxide concentration stimulates receptor cells
  • These send impulses to the muscles of the lungs, causing them to contract faster and more strongly
  • This causes the frequency and depth of breathing to increase until the carbon dioxide concentration of the blood has lowered sufficiently

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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