Final answer:
Contractile vacuoles in paramecia are essential for expelling excess water and waste, maintaining osmotic balance, and preventing cell bursting in hypotonic environments.
Step-by-step explanation:
In paramecia, contractile vacuoles play a crucial role in osmoregulation by expelling excess water and waste from the cell body. This process, executed by exocytosis, is essential for maintaining the cell's osmotic balance, particularly in a hypotonic environment. Contractile vacuoles collect water that enters the cell through osmosis, and when full, these vacuoles merge with the cell membrane to push the water out, preventing the paramecium from bursting from excess water intake.