nots on the lungs for AQA AS biology

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The mechanism of breathing

Inspiration and Expiration

movement of air : In Out

volume of thoratic cavity :High Low

intercostal muscles : External contract Internal contract

movement of ribs : Up and out Down and in

shape of diphragm : Flat Dome

atmospheric pressure : Higher Lower

pulmonary pressure : Lower Higher

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Inspiration ( inhilation)

atmospheric pressure is greater than pulmonary pressure = air forced in lungs

Expiration (exhilation)

pulmonary pressure is greater than atmospheric pressure = air forced out lungs

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Exchange of gases


  • large surface area
  • good blood supply, maintain conc. gradient
  • thin, short diffusion path
  • partially permeable membrane


  • 300 million
  • 70m2
  • lined with thin epithelial cells
  • network of pulmonary capillaries 7-10 micro meters , RBCs are flattened against walls = allows more time for diffusion
  • capillaries have one cell thick walls
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Nice :) Thank you

sarahish majid

thankyou :) rate 5/5

sarahish majid

whats pulmonary and atmospheric pressure? 

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