BRAINCAKEGas Exchange in Fish
Fish face a harder gas exchange problem than land animals, because water is a poor source of oxygen:
• water holds far less dissolved oxygen than the same volume of air (roughly 1/30 as much at ordinary temperatures), and less still when the water is warm
• oxygen diffuses about 10 000 times more slowly in water than in air
• water is dense and viscous, so moving it over a surface takes a lot of energy
Fish are also relatively large, active animals with a small surface area to volume ratio. Their body surface is covered by scales and is not permeable enough for gas exchange, and diffusion across it could not supply their inner cells anyway.
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Key terms in this lesson
- countercurrent exchange
- A system in which two fluids flow in opposite directions, maintaining a diffusion gradient along the whole length of the exchange surface.
More in Gas Exchange
- Protecting the Lungs
- Gas Exchange in Insects
- The Tracheal System
- Very Active Insects
- Fish Gills
- Ventilating the Gills
- The Countercurrent Exchange System
- Gas Exchange in Plants
All 23 lessons in Gas Exchange · All Edexcel AS-level Biology topics