Question

What is cryopreservation?

Answer 1

Preservation is a process of saving something from being spoiled. Generally, the presence of water in food allows microorganisms to grow causing food spoilage. Hence food preservation techniques include processes that alter the water availability like the addition of salts or increasing temperatures. Similarly, organelles, cells, tissues, or any other biological component is subjected to damage. Therefore, there is a need for preservation.

Complete answer:
Preservation by cooling to very low temperatures is known as cryopreservation. Typically solid carbon dioxide at -80ᵒC or liquid nitrogen at -196ᵒC is used to obtain low temperatures. At such low temperatures, the cell loses its enzymatic or chemical activity decreasing the chance of damage. However, damage may be caused due to the formation of ice crystals. This can be minimized by the use of cryoprotectants. Inherent toxicity of cryoprotectants has been reported leading to leaving scope for the development of new methods for cryopreservation.
Cryopreservation has also been observed naturally in certain multicellular microscopic organisms that replace their water content with the sugar, trehalose. Thus reducing the damage to their organelles at freezing temperatures.
Certain risks have been identified in this method like increased salt concentration, extracellular as well as intracellular ice-crystal formation, and dehydration. These risks can be minimized by slowly freezing the samples at a controlled rate or by flash freezing, a process called vitrification.
Over the years scientists have used this technique to freeze biological samples like embryos, reproductive tissues, and important microbial strains.

Note: Although refrigeration allows the storage of microbial cultures for a short time. When stored for longer periods, it may lead to mutation and changes in phenotypic characters. Thus, cryopreservation techniques are also applied to storing cultures. This is done by mixing the liquid cultures with an equal amount of glycerol.