What is the process of preserving cells or whole tissues at extremely low temperatures called?

The process of preserving cells or whole tissues at extremely low temperatures is referred to as cryopreservation. This technique is crucial in various fields, including cell biology, reproductive medicine, and organ transplantation, as it helps to maintain the viability and function of cells and tissues over extended periods. By cooling biological samples to very low temperatures, typically in liquid nitrogen, cellular metabolism slows significantly, halting the degradation processes that would otherwise occur, thus preserving the structural integrity and functional characteristics of the cells.

Other processes listed, such as dehydration, transfusion, and rehydration, serve different purposes and do not involve preserving biological samples at low temperatures. Dehydration refers to the removal of water from cells or tissues, transfusion is the process of transferring blood or blood products into an individual, and rehydration involves restoring moisture to cells or tissues. None of these processes involve the extreme cold that characterizes cryopreservation.