Fig. 1. LLPS involvement in cell volume sensing and regulation. Cell volume perturbation causes three intracellular changes: 1) changes in mechanical forces on membrane sensors, 2) changes in intracellular ionic strength/concentration and 3) changes in macromolecular crowding. These intracellular changes lead to effective cellular responses, including the direct and indirect coordination of water and ion-transporting systems, gene expression, protein quality control and protection of biomolecules for cell volume recovery and adaptation. Although these alterations have been interpreted mainly from the perspectives of biochemistry and molecular biology, recent studies provide a spatiotemporal understanding of these functional alterations with biomolecular condensates induced by liquid-liquid phase separation (LLPS). The "lens" of LLPS enables us to understand the complicated cell volume regulatory mechanism and break through gaps between cell biology and biochemistry/molecular biology interpretations.