AQA GCSE Biology

Revision Notes

4.2.2 Response to Exercise

Effect of Exercise

  • In order for an individual to be able to move, their muscles need to contract, which requires energy from respiration
  • When exercising, the number of muscle contractions increases, therefore there is a greater energy demand, which means that the muscles need a greater supply of oxygen for aerobic respiration
  • The human body reacts to the increased demand for oxygen in a number of ways:
    • The breathing rate and breath volume increase during exercise to increase the amount of oxygen absorbed into the bloodstream by diffusion, and the amount of carbon dioxide removed
    • The heart rate increases
  • These reactions increase the supply of oxygenated blood to the muscles
  • If exercising vigorously, the body may not be able to supply sufficient oxygen to the muscles to meet the demand for energy
  • In this situation, some of the energy supplied to the muscles comes from anaerobic respiration, which is the incomplete breakdown of glucose without oxygen
  • This releases much less energy than aerobic respiration and results in the formation of lactic acid as glucose is incompletely oxidised
  • An “oxygen debt” is created after exercising in this way; it is a debt as “extra” oxygen is needed to react with the lactic acid produced via anaerobic respiration
  • This is why an individual still breathes heavily at an increased rate (with a higher heart rate than usual) after exercising vigorously
    • “Extra” carbon dioxide also has to be removed from the body
  • During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently as a result of increased levels of lactic acid building up

Investigations into the effect of exercise on the body

  • It is relatively simple to investigate the effects of exercise on the body in the classroom
  • Breathing rate can be measured by counting the number of breaths per minute, while heart rate can be measured by taking a pulse
  • Either can be measured before and after an activity is performed and the results plotted on a bar chart
    • It is important that the time over which breathing rate and pulse rate are measured is consistent, and that individuals fully recover (rest) before starting a new activity
Higher Tier Only

Oxygen Debt

  • The body can deal with lactic acid in one of two ways
  • It can be oxidised (reacted with oxygen) to form carbon dioxide and water – the same products formed in aerobic respiration
  • Alternatively, blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose
  • Remember the “oxygen debt” is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells

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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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