**11.2 Addition of cryoprotectants**

To prevent the damage resulting from abrupt freezing or thawing, the chemicals such as glycerol, alcohol, dimethyl sulfate, glycerol, praline, etc. are being added for the purpose of conservation. This protectant referred to as cryoprotectants are added to protect freeze cells or low freezing temperatures etc. But the limitation of the procedure is that only a few biological materials can be frozen below the minus temperature in presence of gas without affecting the viability of cell structures. Liquid nitrogen is used because of the following reasons;

