How a Swim Bladder Works

The swim bladder is perhaps the major key to the teleosts' success, and it is well worth a digression to explain it. It is an internal bladder filled with gas, which can be sensitively adjusted to keep the fish in hydrostatic equilibrium at any desired depth. If you ever played with a Cartesian Diver as a child you'll recognize the principle, but a teleost fish uses an interesting variant of it. A Cartesian Diver is a little toy whose business part is a tiny upended cup, containing a bubble of air, floating at equilibrium in a bottle of water. The number of molecules of air in the bubble is fixed, but you can decrease the volume (and increase the pressure, following Boyle's Law*) by pressing down on the cork in the bottle. Or you can increase the volume of air (and decrease the pressure of the bubble) by raising the cork. The effect is best achieved with one of those stout screw stoppers they put on cider bottles. When you lower or raise the stopper, the diver moves down or up until it reaches its new point of hydrostatic equilibrium. You can coax the diver up and down the bottle by sensitive adjustments to the stopper, and hence to the pressure.


A crucial adaptation for life in the sea.

Folksonomies: biology adaptation

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Bottle (0.976625): dbpedia | freebase | opencyc
Pressure (0.804015): dbpedia | freebase | opencyc
Thermodynamics (0.765331): dbpedia | freebase
Stopper (0.697987): dbpedia | yago
Actinopterygii (0.686723): dbpedia | freebase
Buoyancy (0.683303): dbpedia | freebase
Wine packaging and storage (0.605130): dbpedia
Key signature (0.586485): dbpedia | freebase

 The Greatest Show on Earth: The Evidence for Evolution
Books, Brochures, and Chapters>Book:  Dawkins, Richard (2010-08-24), The Greatest Show on Earth: The Evidence for Evolution, Free Press, Retrieved on 2011-05-19
Folksonomies: evolution science


05 JUN 2011

 Raising Enlightened Children

Memes about raising children as a spiritual naturalist, with a sense of awe for the Universe and reverence for the laws of nature.