Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologymediummcq1 pt

Ice floats on liquid water, unlike the solid form of nearly every other substance. Which statement explains this behavior and its biological consequence?

A.Trapped air bubbles lower the average density regardless of molecular arrangement.
B.Cooling makes any liquid denser, so ice should sink just like frozen gases do.
C.Dissolved salt pushes floating ice upward through osmotic pressure.
D.Hydrogen bonds lock molecules into an open lattice with extra space, making solid water less dense and insulating the liquid below.

Explanation

Core Concept

As water cools toward freezing, each molecule settles into a tetrahedral hydrogen-bonded network that holds neighbors farther apart than in the jostled liquid. The open crystal therefore has lower density than liquid water, so it floats. A floating ice sheet shields the warmer water beneath from frigid air, so lakes freeze from the top down while fish, amphibians, and aquatic plants survive in the liquid layer below. If ice sank, ponds would freeze solid from the bottom and eliminate most aquatic life.

Correct Answer

DHydrogen bonds lock molecules into an open lattice with extra space, making solid water less dense and insulating the liquid below.

More Unit 1: Chemistry of Life practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 1: Chemistry of Life Questions →