Summary

You explored the following essential question in this lesson:

• What chemical and physical properties of water make water an important part of biogeochemical cycles?

As you explored this question, you learned about the hydrologic cycle and about water's primary role as a solvent for many substances. As you will see in Lesson 4, the abundance and quality of water influences other biogeochemical cycles to allow for the transport of substances within the biosphere. You also learned that water is a polar molecule and that its polarity enables water molecules to form hydrogen bonds. Hydrogen bonds contribute to water's high surface tension and its high heat capacity.

Finally, you determined that the use, or overuse, of water by society may eventually have a negative impact on the hydrologic cycle and the biosphere as a whole. You learned that approximately 70% of Earth's surface is covered by water. Since a finite amount of water exists on Earth, the hydrologic cycle is necessary and cannot be jeopardized by human activities. Keep the hydrologic cycle in mind as you study other biogeochemical cycles in the next lessons. Get a better grasp of the magnitude of the role of water in keeping you and your backyard alive.

 Lesson Glossary

adhesion: the tendency of unlike molecules to cling together because of attractive forces

Water is adhesive also due to polarity — the negative and positively charged molecules in water attract other ionic molecules.

cohesion: inter-molecular attraction between like-molecules of a substance

Water is strongly cohesive due to the polarity of its molecules.

heat capacity: the amount of heat energy (J) required to change the temperature of one gram of a substance by 1°C

Water has a high heat capacity of 4.19 J/g °C.