Final answer:
Ice crystals forming in tissues are harmful because they expand and rupture cell membranes, causing irreversible cell damage.
Step-by-step explanation:
Ice crystals are harmful to tissues because they cause the expansion of ice relative to liquid water. The detrimental effect of this expansion is the rupturing of delicate cell membranes, which are essential for the survival and function of the cells. When cells freeze, ice crystals form and expand, leading to irreversible damage. Organisms have adapted to this problem by using substances like glycerol to replace water, thus avoiding the formation of damaging ice crystals during the freezing process.