Contractile vacuole is a sub-cellular structure
(or organelle) which is found primarily in protists (for eg,
Amoeba) and unicellular algae. Contractile vacuole is
responsible for excretion and osmoregulation. It absorbs
excess water and wastes from a microorganism's cell and
excretes them into the environment by contracting.
Contractile vacuoles function in a periodic cycle by
expanding while collecting water and contracting to release
the water.