Why/how multicellular organisms have evolved gaseous exchange

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  • Created by: katie
  • Created on: 23-03-13 16:30
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  • Why/how multicellular organisms have evolved gaseous exchange
    • metabolic needs are proportional to volume. Larger organisms need more oxygen 
    • Larger organisms external surface insufficient for gas exchange 
    • diffusion of respiratory gases proportional to surface area 
    • surface area : volume ratio is too small/ larger animals have a smaller SA: vol ratio to supply metabolic needs
    • diffusion distances too large 
    • not enough O2 can diffuse / O2 cannot diffuse fast enough to the cells furthest from surface to meet metabolic needs
    • gas exchange surface folded/ large number of alveoli - to increase surface area 
    • internal lungs 
    • to reduce water / heat loss
    • gaseous exchange takes place in the alveoli 
    • thin walls - reduce diffusion distance 
    • layer of moisture – for gases to dissolve in 
    • blood supply in capillaries – maintain concentration gradient between alveolar air and blood
    • haemoglobin in erythrocytes – transport of oxygen 
    • ventilation mechanism e.g. lungs
      • -intercostal muscles contract. Diaphragm contracts.
        • Ribs pulled up+out. Diaphragm flattens
          • Increased volume of thorax. Decrece pressure in lungs
            • Air in to replace stale air with fresh air to enable continuous exchange of gases 
  • Ribs pulled up+out. Diaphragm flattens
    • Increased volume of thorax. Decrece pressure in lungs
      • Air in to replace stale air with fresh air to enable continuous exchange of gases 

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