The osmotic expansion of cells maintained in water is mainly regulated byARibosomesBVacuoleCchloroplastDMitochondriaAnswer: B. Vacuole Read Explanation: The main regulator of the osmotic expansion of cells maintained in water is the vacuole. It uses osmosis to regulate the amount of water and other solutes that enter or exit a cell, maintaining the pressure inside it. The mitochondria and chloroplast also play important roles in this process, but they are not the primary regulators. Ribosomes, on the other hand, are mainly responsible for protein synthesis within the cell. Read more in App