Why can liquid nitrogen be useful in plant DNA isolation?

Correct answer: To quickly freeze tissue for grinding

The direct answer is A: liquid nitrogen quickly freezes plant tissue and makes it brittle for grinding. Plant cells have tough walls, so efficient disruption is needed before DNA can be released. Step by step: fresh tissue is exposed to very cold liquid nitrogen; water in the tissue freezes rapidly; the tissue becomes hard and brittle; grinding breaks the cells into a fine powder; DNA can then be extracted more efficiently. Rapid freezing can also slow enzyme activity, including nucleases that might otherwise degrade DNA, although careful handling and a suitable extraction method remain necessary. Option A is correct. Option B is wrong because liquid nitrogen is used to cool and preserve material, not burn DNA. Option C is wrong because it does not convert protein into sugar; that would require different biochemical processes. Option D is wrong because ethanol removal is achieved by washing, evaporation or other protocol steps, not by the main purpose of liquid nitrogen. Liquid nitrogen is extremely cold and requires trained handling and proper protective equipment. Memory cue: liquid nitrogen makes plant tissue “freeze, become brittle, and grind.”