Practice question

Liquid nitrogen provides ultralow storage temperature of -196°C at atmospheric pressure, close to its boiling point. At this temperature, kinetic energy of molecules becomes extremely low, effectively halting all biochemical reactions, enzymatic activity, solute diffusion, and ice recrystallization processes. Cells suspended in DMSO-containing freezing medium enter glassy state preventing further ice growth. Long-term viability preserved for decades to theoretically indefinitely. Mechanical ultra-low freezers at -80°C slow metabolism but do not fully arrest chemical reactions; free radical accumulation and gradual ice crystal growth over months reduce viability, making -80°C suitable only for temporary holding. Storage can be in liquid phase immersing vials directly achieving -196°C or vapor phase at -150°C to -180°C reducing risk of cross-contamination between leaky vials and transmission of adventitious agents. Inventory systems with alphanumeric racking, cryovial labeling resistant to nitrogen, and continuous temperature alarms with liquid nitrogen level monitors ensure security of master and working cell banks including valuable induced pluripotent stem cells.