Gaseous Exchange

Gaseous Exchange

1. Plants

   • leaves
     • thin, flat and large Surface Area
       • shorter diffusion path
     • lots of Stomata
     • lots of air spaces in Spongy Mesophyll
   • Diffusion

2. Single-Celled Organisms

   • large Surface Area:Volume ratio
   • Diffusion is sufficient due to size
   • thin Cell Surface Membrane
     • short diffusion pathway

3. Insects

   • Trachae
     • give large Surface Area
   • lots of Spiracles
     • short diffusion pathway
   • active insects have muscles to Ventilate Trachae
     • maintains high Concentration Gradient
   • Diffusion in gas phase - faster

4. Fish

   • Gill Filaments and Lamellae provide massive Surface Area
   • Lamellae
     • lots of capillaries
     • thin surface layer
       • faster Diffusion
   • Counter-Current system
     • maintains high Concentration Gradient

5. Humans

   • Lung Diseases
   • Ventilation
     • maintains high Concentration Gradient
     • Inhalation
       • Ribs UP Muscles DOWN Volume UP Pressure DOWN
         • Muscles = Diaphragm and External Intercostals contract
     • Exhalation
       • Ribs DOWN Muscles UP Volume DOWN Pressure UP
         • Muscles = Diaphragm and External Intercostals relax
     • when at rest, Tidal and Passive
     • when exercising, Internal Intercostals contract too, pulling ribs down further and increasing volume in thorax more; muscles in abdomen wall contract, pushing diaphragm up further, increasing volume exhaled
     • Pulmonary Ventilation = Tidal Volume x Ventilation Rate
       • PULMONARY VENTILATION: total vol of air moved into lungs during one minute
       • TIDAL VOLUME: vol of gas inspired/expired during each unforced ventilation cycle
       • VENTILATION RATE: number of breaths per minute
   • lots of Alveoli
     • large surface area
     • surrounded by Capillaries
       • maintain conc grad
     • short partially-permeable diffusion pathway
       • RBCs compressed against capillary wall
     • moist surface in which oxygen dissolves to help diffusion

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