What is the term for the preservation of cells or tissues at extremely low temperatures?

Cryopreservation is the term used to describe the preservation of cells or tissues at extremely low temperatures, typically using liquid nitrogen. This method effectively halts all biological activity, including the degradation of cells, by slowing down metabolic processes and reducing the effects of ice crystal formation that can damage cellular structures. By maintaining samples at these low temperatures, researchers and medical professionals can store biological materials for long periods while retaining their viability for future use, such as in transplantation, research, and therapeutic applications. This technique is particularly valuable in fields such as reproductive medicine, stem cell research, and biobanking.

The other options, while related to various preservation methods, do not specifically denote the extreme low-temperature storage that characterizes cryopreservation. Fixation refers to the process of preserving tissue specimens in a way that maintains their structure, often for microscopic examination. Freezing is a more general term that may apply to various preservation methods but lacks the specificity and technical application that cryopreservation provides. Dehydration is a method used to remove moisture from substances, which is not aimed at preserving biological activity as effectively as cryopreservation does.