Explaining the Link Between Physical Activity & Breathing (Cambridge International IGCSE Science)

Explaining the Link Between Physical Activity & Breathing: Extended

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

Exam Hint Be sure not to confuse the terms respiration and breathing in this topic:

• Respiration is a series of chemical reactions that releases energy from food
• Breathing is the mechanism for moving air in and out of the lungs; this supports the chemical reactions of respiration