GCSE Biology (AQA)

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Exchange in Fish

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Cell Biology Transport in Cells

Exchange in Fish

2:35 Diffusion in Action
Spec 4.1.3.1
Previous Diffusion in the Intestines Next Defining Osmosis
  • Fish absorb dissolved oxygen from water through diffusion across their gills into the blood.
  • Gills are located under a bony flap and function similarly to human lungs.
  • Water containing dissolved oxygen enters through the fish's mouth and exits through the gills.
  • Fish opening and closing their mouths is part of the breathing process.
  • Gills are adapted for gas exchange by having thin layers of tissue and a large surface area.
  • Gills are divided into many sections and layers, increasing the surface area for diffusion.
  • Continuous water flow over the gills maintains a steep concentration gradient, essential for efficient gas exchange.
  • Gills are well ventilated, ensuring a constant flow of water.
  • Water flows across the gills, where oxygen is absorbed and carbon dioxide is expelled.
  • Gills contain rich capillary networks that facilitate efficient blood supply and gas circulation.
  • Blood flows around the gills, turning from deoxygenated (blue) to oxygenated (red) as gases are exchanged.
  • Oxygen diffuses from high concentrations in the water to lower concentrations in the blood, while carbon dioxide diffuses from higher concentrations in the blood to lower concentrations in the water.
  • Key features increasing gill effectiveness include a large surface area, thin membrane, efficient blood supply, and good ventilation.

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