Adaptations to gas exchange in insects

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  • Insects
    • To reduce water loss, insects have evolved a rigid exoskeleton made of chitin
    • Insects have a relatively small surface area to volume ratio, so cannot use their body surface to exchange gases by diffusion
    • They have evolved a different system of gas exchange to other land animals
      • Gas exchange occurs through paired holes called spiracles, running along the side of the body
        • The spiracles lead into a system of chitin lined air tubes called tracheae
          • Spiracles can open and close like valves. This allows gas exchange to take place but reduced water loss
            • The ends of the tracheal branches are called tracheoles. The tracheoles are the gas exchange surfaces, they come into contact directly with every tissue
    • Every cell in an insect is only a short distance from the tracheoles so the diffusion pathway is short
      • At rest, gas exchange takes place simply by passive diffusion via the spiracles
        • During activity, muscles in the thorax and abdomen contract and relax, causing movements of the abdomen which help ventilate the tracheae and maintain a concentration gradient
    • Advantages of insect adaptations
      • Every tissue is directly supplied with oxygen
      • No haemoglobin is needed
      • Reduced water loss


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