Response to Exercise (AQA GCSE Biology: Combined Science)

• 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

• 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