If cells are placed in a hypertonic solution, what happens?

• A. They shrink
• B. They swell
• C. They become more permeable
• D. They lyse

Answer: (A)

Water moves from the inside of the cell to the outside in a hypertonic environment because the surrounding solution has a higher solute concentration. This osmotic flow of water out of the cell causes the cell to lose volume and shrink (crenation in many cell types). The other outcomes don’t fit: swelling would happen if the outside were less concentrated (hypotonic), increasing permeability isn’t a direct result of hypertonicity, and lysis requires the cell to swell and burst, which doesn’t occur in a hypertonic setting.