Re: why is a contractile vacuoles little value to organisms living in oceanH2O?

Hi Natalie,

As you may know, the contractile vacuole is a specialized compartment that 
is designed to collect excess water in the cell. Contractile vacuoles are 
pretty much limited to some protists and sponges that live in fresh water. 
Protists that live in fresh water environments are subjected to a 
continuous influx of water. The solute concentration inside the cell is 
higher than that in the surrounding water so water continuously diffuses 
in. If cells are to maintain a steady internal solute concentration, water 
must be removed from the cell (against its concentration gradient) at the 
same rate at which it enters. This process is called osmoregulation. Water 
always likes to flow to the environment that has the higher solute 
concentration.  In the ocean, you might recall that the environment is 
very salty. So the solute concentration is higher outside the cell instead 
of inside the cell. In this case, water will flow out of the cell into the 
ocean instead of going into the cell. Thus, the protist doesn't need a 
contractile vacuole to pump out water in the ocean.
 
In the archives of Madsci.org I found an excellent explaination of 
osmoregulation that will help you understand why in the ocean a 
contractile vacuole is not needed.
 htt
p://www.madsci.org/posts/archives/jan2000/949345895.Cb.r.html

Have fun with science!
Elsa