Ventilation in Fish and Insects

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  • Created by: Freja
  • Created on: 09-04-21 13:56
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  • Ventilation and Gas Exchange in other Organisms
    • Insects
      • How does gas exchange take place?
        • Diffusion gradient
          • Oxygen moves down a concentration gradient from the air into body cells
          • Carbon dioxide moves down a concentration gradient from body cells into the air
        • Ventilation by rhythmic abdominal movements
          • Further speeds up the exchange of respiratory gases by generating mass movements of air in and out of the tracheal tubes
          • Rhythmic abdominal movements  change  the volume of their bodies and move air in and out of the spiracles
      • Gas Exchange
        • Insects have microscopic air-filled pipes called trachea, which are used for gas exchange
        • The trachea branch off into smaller tracheoles which have thin, permeable walls and go into individual cells
          • The tracheoles also contain fluid, which oxygen dissolves in
            • The oxygen the diffuses from this fluid into body cells and carbon dioxide diffuses in the opposite direction
      • Dissection
        • Fix the insect to a dissecting board and you can put dissecting pins through the legs to hold it in place
          • To examine the trachea, you need to carefully cut and remove a piece of exoskeleton from the length of the insects abdomen
            • Use a syringe to fill the abdomen with saline solution.
              • You should be able to see a network of very thin, silvery-grey tubes (the trachea), and they look silver as they are filled with air
                • You can examine the trachea using a light microscope and a wet mount slide
                  • You should be able to see rings of chitin in the walls of the trachea and they are there for support
    • Fish
      • Dissection
        • Place the fish in a dissection tray or on a cutting board
          • Push back the operculum and use scissors to remove the gills. Cut each gill arch through the bone at the top and bottom
            • You should be able to see the gill filaments
              • Finish by drawing the gill and then label it
      • Ventiltion
        • The fish opens its mouth, which lowers the floor of the buccal cavity. So the volume of the buccal cavity increases, which decreases the pressure inside the cavity. Water is then sucked in to the cavity.
        • When the fish closes its mouth, the floor of the buccal cavity is raised again. The volume inside the mouth decreases so the pressure increases and water is forced out of the cavity across the gill filaments.
        • Each gill is covered by a bony flap called the operculum, which protects the gill. The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills.
      • Gas exchange
        • Fish use a counter-current system for gas exchange
        • Water containing oxygen enters the fish through its mouth and passes out through the gills
        • Each gill is made of lots of thin branches called gill filaments, which gives a large surface for exchange of gasses
        • The gill filaments are covered in lots of tiny structures called gill plates, which increase the surface area more. Each gill is supported by a gill arch
        • The gill plates have lots of blood capillaries and a thin surface layer of cells to speed up diffusion
        • Blood flows through the gill plates in one direction and water flows over in the opposite direction. This is the counter-current system.
          • It maintains a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood

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