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cryoprotectant A substance that helps to protect an organism's tissues from the effects of freezing. Cryoprotectants are vital to the survival of those organisms living in cold climates that adopt a strategy of tolerating a limited amount of freezing of their tissue fluids. Such organisms include certain insects, molluscs, and nematodes, and even some frogs, lizards, and turtles. One group of these substances consists of antifreeze molecules, notably glycerol and related polyhydric alcohols (polyols). Another group of cryoprotectants bind to membranes within cells and prevent the binding of water molecules, so preserving the integrity of cell structures. Examples in insects include proline and trehalose. See also ice-nucleating agent.