Gas exchange systems

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  • Gas exchange systems
    • Insects
      • Rigid exoskeleton which is waterproof, openenings called spiracles lead to tubes called tracheae which branch into tracheoles. These are held open by rings of hard chitin. Tracheoles penetrate deep into the insects tissues, carrying oxygen directly to every cell. Spiricles open and close to allow oxygen to diffuse down its concentration gradient to its tissues. Whenever the spiracles are open water is lost.
    • Fish
      • Specialised gas organs because they have a small surface area : volume ratio. Gills are composed of thousands of filaments which are covered in tiny lamellae. Fish ventilate through water but fish ventilation is one-way.
        • Water enters the buccal cavity, passes over the gills and exits through thr opercula valves. Diffusion of oxygen is due to 3 things: large surface area from the high number of lamellae that filaments are covered with, short diffusion distance because lamella are only a few cells thick and contain blood capillaries, a concentration gradient is maintained by the countercurrent system: blood and water flow side by side, water always has a higher oxygen concentration than blood - a concentration gradient exists along the whole of the lamella.
    • Plants
      • Plants must respire all the time to produce ATP.
        • Gas exchange suface is made up up the spongy mesophyll tissue within the leaf which are loosely packed and so increases the surface area for gas exchange. Gases enter and leave the leaf through stomatal pores. There is a short diffusion pathway between them and the mesophyll cells. Many air spaces for gases to circulate between cells. The concentration gradients for these gases are maintained.
  • Water enters the buccal cavity, passes over the gills and exits through thr opercula valves. Diffusion of oxygen is due to 3 things: large surface area from the high number of lamellae that filaments are covered with, short diffusion distance because lamella are only a few cells thick and contain blood capillaries, a concentration gradient is maintained by the countercurrent system: blood and water flow side by side, water always has a higher oxygen concentration than blood - a concentration gradient exists along the whole of the lamella.

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