Which one of the following cell organelles may play a role in expelling excess water and wastes in case of unicellular organisms?

In unicellular organisms, particularly freshwater protozoans like Amoeba and Paramecium, the contractile vacuole is a specialized organelle essential for osmoregulation and excretion. These organisms live in hypotonic environments where water constantly enters the cell via osmosis. The contractile vacuole collects this excess water along with dissolved metabolic wastes and periodically contracts to expel the contents out of the cell through the plasma membrane [3]. While many unicellular organisms also rely on simple diffusion across the body surface for waste removal [2], the contractile vacuole specifically manages water balance to prevent the cell from bursting. Other organelles like lysosomes are primarily involved in intracellular digestion, the Golgi body in packaging and secretion, and the endoplasmic reticulum in protein and lipid synthesis. Thus, the contractile vacuole is the primary organelle for expelling excess water and wastes in these single-celled life forms.

Sources

1. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > 5.2.4 Nutrition in Human Beings > p. 84
2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 2: The Invisible Living World: Beyond Our Naked Eye > A step further > p. 13