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Which of the following is a cryoprotectant?
(A) Mannitol
(C) Ethylene oxide
(D) All of the above

Last updated date: 11th Jun 2024
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Hint: The word ‘cryo’ refers to extreme cold. Cryoprotectant is any chemical which is used to prevent cells from extreme cold or freezing damage when they are preserved in liquid nitrogen tanks. Seeds, embryos, plant and animal cells are all stored at extreme cold temperatures, in order to be utilised in the future.

Complete answer:
The word ‘cryo’ is derived from the Greek word ‘kryos’ meaning ice cold or frost. Cryoprotectant refers to any chemical substance that has the ability to prevent cells from extreme cold or freezing damage. Cryoprotectant is extremely used in seed banks, sperm banks in order to preserve cells at -196˚C, for future use. Nowadays, cells of all kinds like embryos, tissues, eggs, stem cells and even organs are preserved.

Cryoprotectant functions by penetrating into the cell and increasing the solute concentration inside the cell. Since, they function only by penetrating the cell, they should not be toxic to the cells. They also function by forming hydrogen bonds with the biomolecules, displacing the water molecules. Usually, a combination of cryoprotectants are used rather than a single agent, as they impose less toxicity.
Chemicals such as alcohols containing two hydroxyl groups are often used as conventional cryoprotectants. Examples of frequently used cryoprotectants are ethylene glycol, propylene glycol, glycerol and DMSO (Dimethyl sulfoxide). Cryoprotectants are also used as preservatives to preserve foods such as raw chicken. These chemicals are usually sugars and sodium phosphates as they are less toxic to food.

Hence, the correct answer is Option (B)

Note: It is important to remember the exact definition of cryoprotectant and its functions. All the cryoprotectants preserve the cell and prevent it from freezing damage only by penetrating into the cell. They increase the solute concentration inside the cell, thus by preventing the formation of ice crystals in the cell.