Water is a powerful insulator. When water is heated or cooled, its temperature changes more slowly than other liquids. This resistance to gaining or losing heat is due to the high specific heat of water. Because of water’s unique molecular and bonding structure, heat must first break the hydrogen bonds between the molecules, rather than immediately speeding up the molecules and thereby increasing their temperature. This allows water to serve as a “heat sink”; it absorbs heat without rapid changes in temperature which helps buffer aquatic organisms from large swings in temperature.
Water’s high specific heat allows large bodies of water to absorb significant heat during the summer without a rapid increase in water temperature. At night, large bodies of water cool very little, providing a relatively stable temperature, and during the winter, water’s gradual release of heat energy warms the air, giving coastal areas a milder ‘maritime’ climate. The moderation of water temperature is vitally necessary for the plants and animals living in aquatic and marine ecosystems.
Water is required for many chemical reactions necessary to life. It is a key component, for instance, in metabolism—or the series of chemical reactions that allow organisms to live, grow, and reproduce. The type and purpose of each metabolic process is unique, but photosynthesis (see Figure 5) is one well-known example. In this process, plants use radiant energy from the sun and carbon dioxide (CO2) from the atmosphere, and water from the soil to produce chemical energy in the form of sugar (glucose, C6H12O6). Plants release oxygen (O2) as a by-product of photosynthesis. The oxygen in our atmosphere enables plants, animals, and micro-organisms to live and undergo cellular respiration. The ultimate source of this life-giving oxygen is the water molecules that are absorbed by the plants’ roots. You will learn more about the importance of photosynthesis in Chapter 3 on energy.
Questions to Consider
- Imagine how the fresh water supply in your community will be modified by a warming climate. What effect would this have on water availability in your community?
- Imagine that the fresh water supply in your community became so polluted that it lost a good deal of its solvency. What effect would this have on the use of water in your community?
- What are the properties of water that make it essential for life on earth?