Spheroplasts are osmotically fragile, and will lyse if transferred to a hypotonic solution. Colestyramine prevents this increase in water by making the bile acids insoluble and osmotically inactive. Because it is soluble in water, it is osmotically active. During slow cooling, ice forms extracellularly, causing water to osmotically leave cells, thereby dehydrating them. It is unclear whether it made food via photosynthesis, or osmotically extracted nutrients from seawater. Osmotherapy is the use of osmotically active substances to reduce the volume of intracranial contents. All four are osmotically active substances found in humans. The reverse happens in freshwater fish&colon; they tend to gain water osmotically.