alveoli (9 mark)

• Why is having many alveoli important?

  Increases surface area for faster gas exchange
• Why are alveolar walls only one cell thick?

  to shorten the diffusion pathway for gases
• What surrounds each alveolus?

  A dense network of capillaries to maintain a steep concentration gradient
• What role do capillaries play in gas exchange?

  carry deoxygenated blood in and remove CO₂, keeping oxygen concentration high in alveoli
• Why is a moist lining important in alveoli?

  helps dissolve gases so they can diffuse across the membrane
• What is the function of surfactant in alveoli?

  Reduces surface tension to prevent alveoli collapse during exhalation
• Why do alveoli contain elastic tissue?

  for recoil during exhalation aiding ventilation efficiency
• How does blood flow through capillaries aid diffusion?

  ensures continuous removal of CO₂ and supply of O₂, keeping diffusion gradients steep
• How do all these features together help?

  maximise the rate of gas exchange to meet the body's oxygen demands.