Gas exchange

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  • Gas Exchange
    • Gas exchange surfaces
      • Large SA
      • Thin- provides short diffusion pathway
      • Maintains steep concentration gradient of gases
    • Single celled organisms
      • Absorb/release gases by diffusion through outer surface
      • Have relatively large SA, are thin and short diffusion pathway- no need for gas exchange system
    • Fish
      • Lower conc of oxygen in water than air
      • 1) Water containing O2 enters fishes mouth, passes out through gills
      • 2) Each gill is made of gill filaments which provide large SA for exchange of gases
      • 3) Gill filaments covered in lamellae, which increase SA even more
      • 4) Lamellae have lots of blood capillaries and are thin to speed up diffusion
      • 5) Blood flows through lamellae in one direction, water flows opposite way. Counter current system. Maintains large concentration gradient between water and blood. Conc of O2 in water always higher than in blood, so as much oxygen as possible diffuses from water to blood
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    • Insects
      • 1) Insects have microscopic air filled pipes called tracheae used for gas exchange
      • 2) Air moves into tracheae through pores on surface called spiracles
      • 3) O2 travels down conc gradient towards cells
      • 4) Tracheae branch off into tracheoles which have thin, permeable walls and go to individual cells- oxygen can diffuse directly into respiring cells
      • 5) Carbon dioxide from cells moves down own concentration gradient towards spiracles to be released into atmosphere
      • Insects use rhythmic abdominal movements to move air in and out of spiracles


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