AS LEVEL- Biology- Exchange surfaces + Breathing (2)

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  • Exchange surfaces + Breathing (2)
    • Spirometer
      • Tidal volume- volume of air in each breath *Usually about  0.4dm3
        • To measure tidal volume; each curve represents one breath so you would have to measure from the highest peak to the lowest trough + find the difference
      • Vital capacity- the max. volume of air that can be breathed in or out
        • To measure vital capacity; you would look at the highest peak + lowest trough + take them away
      • Breathing rate- how many breaths are taken *Usually in a min
        • To measure the breathing rate; you would count the number of curves as one curve = one breath
      • Oxygen consumption- the rate at which an organism uses up oxygen
        • To measure oxygen consumption; you would draw a line touching the peaks + taking the average slope of the trace
    • Ventilation + gas exchange in insects
      • Insects use tracheae to exchange gases
        • 1) *Insects have microscopic air-filled pipes called tracheae which they use for gas exchange
        • 2) *Air moves into the tracheae through pores on the insect's surface called spiracles
        • 3) *Oxygen travels down the concentration gradient towards the cells *Carbon dioxide from the cells down its own concentration gradient towards the spiracles to be released into the atmosphere
        • 4) *The tracheae branch off into smaller tracheoles which have thin, permeable walls + go to individual cells *The tracheoles also contain fluid, which oxygen dissolve in
        • 5) *The oxygen then diffuses from this fluid into body cells *Carbon dioxide diffuses in the opposite direction
        • 6) *Insects use rhythmic abdominal movements to change the volume of their bodies + move air in + out of the spiracles *When larger insects are flying they use their wing movements to pump their thoraxes too
      • How to dissect the gaseous system in insects
        • 1) *Fix the insect to a dissecting board *You can put dissecting pins through its legs to hold it in place
        • 2) *To examine the tracheae, you'll need to carefully cut + remove a piece of exoskeleton from along the length of the insect's abdomen
        • 3) *Use a syringe to fill the abdomen with saline solution *You should be able to see a network of very thin, silvery-grey tubes- these are the tracheae *They look silver because they're filled with air
        • 4) *You can examine the tracheae under a light microscope using a wet mount slide *Again the tracheae will appear silver/grey *You should be able to see rings of chitin in the wall of the tracheae- these are there for support
    • Ventilation + gas exchange in fish
      • Fish use a counter-current system for gas exchange
        • 1) Water, containing oxygen enters the fish through its mouth + passes out through the gills
        • 2) *Each gill is made of lots of thin branches called gill filaments which give a big SA for exchange of gases *The gill filaments are covered in lots of tiny structures called gill plates which increase the SA even more *Each gill is supported by a gill arch
        • 3) *The gill plates have lots of blood capillaries + a thin surface layer of cells to speed up diffusion
        • 4) *Blood flows through the gill plates in one direction + water flows over in an opposite direction- counter-current system *Maintains a large concentration gradient between the water + blood *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
      • How fill gills are ventilated
        • 1) *The fish opens its mouth which lowers the floor of the buccal cavity (space inside the mouth) *The volume of the buccal cavity increases, decreasing the pressure inside the cavity *Water is then sucked into the cavity
        • 2) *When the fish closes its mouth, the floor of the buccal cavity is raised again *Volume inside the cavity decreases, the pressure increases + water forced out of the cavity across the gill filaments
        • 3) Each gill is covered by a bony flap called the operculum (protects the gill) *The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills
      • How to dissect fish gills
        • 1) Wear an apron, lab coat + gloves
        • 2) Place your fish in a dissection tray
        • 3) Push back the operculum + use scissors to carefully remove the gills. Cut each gill arch through the bone at the top + bottom
        • 4) If you look closely, you should be able to see the gill filaments
        • 5) Finish off by drawing + labelling the gill


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