gas exchange

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Organisms need special exchange surfaces

All living cells need certain substances to keep them alive. 

Some of which include:-

  • Oxgyen - aerobic respiration 
  • Glucose - source of energy 
  • Proteins - growth & repair 
  • fats, water and minerals 

How do the cells get the substances they need

Cells absorb substances from surrounding environment 
Make them - inside cytoplasm (cell metabolism)

Removing substances 

  • CO2
  • O2  


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Organisms need special exchange surfaces

Single celled organisms can diffuse directly across cell membrane 

      • Fast rate of diffusion because movement across outer cells - small distance 
      • Nutrients, waste, gases all exchanged 
      • Large surface-area-volume ratio 

Larger mutlicellular organisms slower because:-

      • surface-area-volume ratio is smaller 
      • Cells need more supplies 
      • Outer surface is not large enough to to enable gases and nutrients to enter body fast enough to keep all cells alive 
      •  Nutrients/gases have further to travel from surface to center of organism 
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Organisms need special exchange surfaces

E.G Mammalian Lung 

Breath in - air enters the Trachea 

Trachea splits in to 2 Bronchi - 1 Bronchus for each lung 

Bronchus branch out into Bronchioles (smaller tubes)

Bronchioles end in small sacs - Alveoli (gas exchange happens here) 

Intercostal muscles, ribcage and diaphragm work together to move air in and out 

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Organisms need special exchange surfaces

Alveoli - Gaseous Exchange Surface 

    • Each alveolus - single layerof thin flat cells - alveolar epithelium 
    • Bunches at end of bronchioles
    • Surrounded by capilaries - each alveoli has its own blood supply

O2 diffuses out of aveoli into blood

CO2 diffuses into aveoli from the blood 

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