How does Paramecium regulate its water content? - Dr. Biology Questions and Answers

Contractile vacuoles act as water pumps for osmoregulation

One paramecium cell has two star-shaped contractile vacuoles sitting on each end of the body. They are filled with fluids and are present at fixed positions between the endoplasm and ectoplasm. Contractile vacuoles are responsible for osmoregulation, or the discharge of excess water from the cell.

The contractile vacuoles act to regulate the quantity of water inside of a cell. In freshwater, which is a hypotonic environment for paramecium, water flows into the cell by osmosis. The contractile vacuoles expel water out of the cell by contracting and prevents the cell from absorbing too much water or even burst.

How does the contractile vacuoles in a Paramecium help maintain homeostasis?

Each contractile vacuole is connected to several radical canals (which form its star shape). Excess water is drained from the whole body of paramecium and fed into the contractile vacuoles via these canals. The accumulation of water makes the vacuole increase in size. Once the reservoir reaches a contain threshold, the contractile vacuole contracts to discharge the excess water through a pore on the pellicle.

Two contractile vacuoles work independently. The posterior contractile vacuole is close to the cytopharynx and hence contract more quickly because of more water passing through. When the contractile vacuole collapses, it may disappear periodically and hence are called temporary organs.

[In this figure] The anatomy of a Paramecium cell.

Extended read:

The Structure of Paramecium Cell

This article covers