Question

Cryopreservation involves preserving cells, tissues and organs in ___A___ at __B___.

• A. A : ice, B : 0°C
• B. A : liquid nitrogen, B : 0°C
• C. A : dry ice, B : -196°C
• D. A : liquid nitrogen, B : -196°C

Answer 1

The correct option is D A : liquid nitrogen, B : -196°C

Cryopreservation is the process of preserving living cells, tissues or organs indefinitely in liquid nitrogen at a very low temperature of -196°C to protect them from any damage caused due to ageing or microbial decay.

Nitrogen gas liquefies at -196°C. Being inert in nature, nitrogen does not react with the samples. So option d is correct and option b is incorrect.

Figure : Cryopreservation

At such low temperatures, all enzymatic or chemical activities of a living cell remain suspended. Cryopreservation uses mechanised controlled freezing which prevents intracellular or extracellular ice formation, which can happen in regular refrigeration processes. Thus, damage to the cells is prevented and the samples are preserved keeping their viability intact.

Tissues, organs, embryos or seeds of threatened (any species vulnerable to endangerment in the near future) and endangered (a species seriously at risk of extinction) species can be conserved using this technique. It serves as an ex-situ (off site) conservation strategy for biodiversity conservation.

Water freezes into ice at 0°C and hence cannot provide temperatures low enough to suspend the metabolic activities of biological samples for an indefinite period. Thus ice is not used in cryopreservation. Hence option a is incorrect.

Dry ice or solid carbon dioxide sublimates (changes into gas) at -78.5°C. Although it is used as a coolant (a liquid or gas that is used to remove heat, it cannot be used for storage of biological things for indefinite periods of time. Hence option c is incorrect.

Figure : Dry ice