Diffusion In Fish Gills

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  • It’s all about partial pressure.
  • In a fish, oxygen moves from the surrounding water through the gills to the blood and finally the tissues. At each step, the oxygen level becomes lower -- otherwise the oxygen wouldn’t diffuse. This graph redrawn from Eckert & Randall (14-13).
  • The numbers here show oxygen concentration as a percent of what the water or blood can hold (saturation). Water and blood carry different amounts of oxygen.
  • Diffusion In Fish Gills

    1. 1. Gas Exchange & Circulation Chapter 4 Gas Exchange in Animals
    2. 2. Why is gas exchange important? C 6 H 12 O 6 + O 2  Energy + CO 2 + H 2 O Energy + CO 2 + H 2 O  C 6 H 12 O 6 + O 2 Photosynthesis: Respiration:
    3. 3. How can an organism get O 2 into its body? Diffusion.
    4. 4. How can an organism get O 2 into its body? <ul><li>For very small organisms, diffusion is fast enough to supply O 2 . </li></ul><ul><li>O 2 use is correlated with body mass (or volume), but diffusion rate depends on surface area... </li></ul><ul><li>and larger organisms have lower surface area/volume ratios. </li></ul>
    5. 5. surface area/volume ratio
    6. 6. How do animals get O 2 ? How do animals get O 2 ? <ul><li>Diffusion alone is enough for animals up to about 1 mm thick... </li></ul><ul><li>depending on rate of O 2 use. </li></ul><ul><li>Larger, faster animals need tricks to speed up diffusion. </li></ul>
    7. 7. O 2 diffuses from high concentration to low concentration.
    8. 8. Speeding up diffusion <ul><li>Gases diffuse from higher to lower concentration. </li></ul><ul><li>Concentraion must be lower in organism than in environment. </li></ul><ul><li>Will organism get enough O 2 ? Depends on rate of O 2 use and diffusion. </li></ul><ul><li>Large, active animals have tricks to speed up diffusion. </li></ul>
    9. 9. Big aquatic animals usually have gills to provide surface area for gas exchange.
    10. 10. Fish usually need more oxygen than invertebrates; they have more gill area than most invertebrates.
    11. 11. Faster fish have bigger gills. index of relative gill surface area Mackerel: 2551 Toadfish: 137
    12. 12. Speeding up diffusion <ul><li>Increase gill surface area; have thin gill epithelium. </li></ul><ul><li>Pump water across gills. </li></ul><ul><li>Pump blood through gills. </li></ul>
    13. 13. Operculum in Fish 1-way flow of water across gills
    14. 14. How fish speed up diffusion: ventilation <ul><li>Fish use energy to pump water across gills (ventilation). </li></ul><ul><li>At low speed, opercular pumping is used. </li></ul><ul><li>Counter current of blood flow over gills </li></ul>
    15. 15. Fish gill structure
    16. 16. Countercurrent exchange of O 2 in gills
    17. 17. <ul><li>Water & blood flow opposite directions. </li></ul><ul><li>This maximizes the concentration gradient & speeds up diffusion. </li></ul><ul><li>Equilibrium is never reached. </li></ul>Countercurrent exchange of O 2 in fish gills

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