Question

Are protozoans presenting contractile vacuoles (also called pulsatile vacuoles) more commonly found in fresh or in salt water?

Answer 1

It is found inside the cell of fresh water protozoan. This is because ,the water present in sea is rich in solute concentration and represents a hypertonic environment compared to the environment present inside the protozoan cell causing the cell to undergo plasmolysis and shirnk in size on the other hand the fresh water tends to have a much lower solute concentration than the one present inside the protozoan cell this leads to diffusion of water molecules from a region of high water concerntration to a region of low water concentration and swell up thus increase the turgidity of the cell , however there is no mechanism present inside the protozoan cell to regulate the turgor pressure generated and this might lead to cytolysis of the cell. So in order to prevent this from happening contractile vacuoles are present inside the fresh water protozoan cell . Contractile vacuoles are specialised vacuoles developed for the function of storing water and release it to maintain the cell osmosity in adverse conditions. When the vacuole release the stored water it dilutes the concentration of solute present inside the plasma membrane thereby establishing an equilibrium with the external hypotonic conditions.