The Lungs (AQA GCSE Biology: Combined Science)

Adaptations for gas exchange

• All gas exchange surfaces have features to increase the efficiency of gas exchange including:
  • Large surface area to allow faster diffusion of gases across the surface
  • Thin walls to ensure diffusion distances remain short
  • Good ventilation with air so that diffusion gradients can be maintained
  • Good blood supply (dense capillary network) to maintain a high concentration gradient so diffusion occurs faster

• Remember that gas exchange occurs by the process of diffusion; breathing is essential in maintaining high concentration gradients between the air in the alveoli and the gases dissolved in the blood
  • In particular, breathing keeps the oxygen level in the alveoli high and the carbon dioxide level low

Structure of the lungs diagram

Each lung contains around 250 - 300 million alveoli, with the total surface area of each lung being around 70m²

Structures in the lungs table