What organelle in protozoans functions to remove excess water from the cell?

The contractile vacuole is the organelle in protozoans responsible for removing excess water from the cell. Protozoans, particularly those living in freshwater environments, face the challenge of osmotic balance due to the movement of water entering the cell through osmosis. As these organisms do not have a rigid cell wall, accumulated water can create internal pressure, potentially leading to cell lysis.

The contractile vacuole acts as a regulatory organelle, collecting excess water that enters the cell and periodically expelling it to maintain osmotic balance. This function is crucial for the survival of protozoans in hypotonic environments, thus highlighting the role of the contractile vacuole in maintaining homeostasis.

Ribosomes are involved in protein synthesis and do not have a role in water regulation. Mitochondria are the powerhouses of the cell, generating ATP through cellular respiration, while chloroplasts are involved in photosynthesis in plants and some protozoans but do not function in water expulsion. Therefore, the contractile vacuole is uniquely suited for the task of removing excess water.