Explaining the Link Between Physical Activity & Breathing: Extended (CIE IGCSE Biology: Co-ordinated Sciences (Double Award))

Extended Tier Only

• Frequency and depth of breathing increase when exercising
• This is because muscles are working harder and aerobically respiring more to keep up with the energy demand:
  • They need more oxygen to be delivered to them
  • Carbon dioxide needs to be removed

Mechanism for increasing breathing during exercise

• The rate of respiration increases in muscle cells when exercising heavily
• CO₂ is a product of aerobic respiration, so CO₂ levels increase in the muscle cells
• This CO₂ diffuses out of the cells into the blood plasma
  • CO₂ in solution causes a slight drop in pH so the blood becomes slightly more acidic
• The blood flows around the circulatory system and passes to the brain where the increased carbon dioxide levels are detected by receptors in the brain
  • Receptors are cells that detect changes in the body
  • The receptors in the brain can detect changes in blood gas (CO₂) levels, as well as changes in pH
• The brain sends nerve impulses to the diaphragm and the intercostal muscles to increase the rate and depth of muscle contraction
• The rate of inspiration increases, along with the volume of air moved in and out with each breath
• The result is greater absorption of oxygen and removal rate of carbon dioxide
  • This supports the increased rate of respiration in the exercising muscle cells