The branch of science deals with study of preservation of cells, tissues and organs in liquid nitrogen is called

The branch of science that deals with study of the preservation of cells, tissues and organs in liquid nitrogen are called Cryobiology.
Cryobiology is the branch of biology that studies the effects of low temperatures on living things within Earth's cryosphere or in science.
Cryobiology is the study of biological material or systems at temperatures below normal. Temperatures may range from moderately hypothermic conditions to cryogenic temperatures.