Final answer:
Sarcodina utilize contractile vacuoles to expel excess water and maintain osmotic balance within the cell, thereby protecting the cell from bursting in a hypotonic environment.
Step-by-step explanation:
Sarcodina, such as the Paramecium, use contractile vacuoles to manage the water balance within their cells. These organisms typically live in a hypotonic environment where the concentration of solutes inside the cell is higher than the surrounding environment. As a result, water tends to flow into the cell by osmosis, which could cause the cell to swell and potentially burst. To prevent this, the contractile vacuoles collect excess water from the cytoplasm and expel it from the cell.
The process starts with the canals surrounding the vacuole, absorbing water from the cytoplasm. This water is then transported into the vacuole which swells as it fills. Once the vacuole is full, it merges with the cell membrane, a process known as exocytosis, and expels the water into the external environment, thus maintaining the cell's osmotic balance and preventing it from rupturing.