Advanced Placement (AP) Biology Practice Exam

What is the significance of water's solid form being less dense than its liquid form?

1. It allows water to evaporate easily.

2. It enables aquatic life to survive in frozen lakes.

3. It helps in the dissolution of ions.

4. It increases the boiling point of water.

The correct answer is: It enables aquatic life to survive in frozen lakes.

Water's solid form, ice, being less dense than its liquid form is significant because it allows ice to float on water. This fundamental property is crucial for the survival of aquatic life in regions that experience freezing temperatures. When bodies of water freeze, ice forms on the surface, creating an insulating layer that maintains a relatively stable temperature for the liquid water below. This insulation prevents the entire body of water from freezing solid, allowing fish, amphibians, and other organisms to survive underneath the ice through the winter months. Therefore, the phenomenon of ice floating not only sustains aquatic ecosystems but also plays a crucial role in maintaining biodiversity in freshwater habitats during cold seasons. The other options do not directly relate to the implications of ice's lower density. For example, the evaporation of water, dissolution processes, and boiling point are significant properties of water, but they are not directly tied to the fact that ice is less dense than liquid water.