CIE IGCSE Biology: 复习笔记：11.1.10 Explaining the Link Between Physical Activity & Breathing: Extended

• 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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