Ice floats on water, and this is biologically important because

  • A. the ice layer insulates the water below, letting aquatic organisms survive the winter
  • B. it allows water to evaporate faster in cold weather
  • C. it increases the amount of oxygen dissolved in the lake
  • D. it lowers the freezing point of the remaining water

Explanation

Water is unusual in becoming less dense as it freezes, because the hydrogen bonds lock the molecules into an open lattice, so ice forms at the surface instead of sinking. The layer then insulates the water beneath, which stays liquid and allows fish and other organisms to survive. If ice sank, a pond would freeze solid from the bottom upwards and life in it would be destroyed.

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