Understanding the Biology of Water: The Structure and Properties of H2O

In the field biology, the most important molecule on earth is water. All organisms on the planet are composed of 70 to 90% water. Water is composed of both hydrogen and oxygen. H2O has unique properties that allow it to help support life. It has several structures and properties that make the molecule unique. Furthermore, it has special abilities involving heat and tension that make it different than any other molecule on earth.

Water is a polar covalent bond, meaning that atoms do not share electrons equally. Because oxygen is more electro-negative than hydrogen, electrons spend more time around the nucleus of oxygen than of hydrogen. This then makes the oxygen become slightly negative and hydrogen become positive which means it is not an ionic bond.

Water can support life for several reasons, for example, it can act as a solvent, it is cohesive, and it has a high surface tension. Because of its polarity water can dissolve substances by acting as a solvent. If a substance is hydrophilic then molecules are attracted to water, but if it is hydrophobic then molecules are not attracted to it. Water is cohesive properties allow its molecules to stay together due to its hydrogen bonding. Additionally, because of adhesion water molecules can cling to other surfaces. Because these molecules stick so closely together, the molecules at the surface stay tighter together than to the air above.

Additionally, water has both a high heat capacity and a high heat of vaporization. Since there are a lot of hydrogen bonds that connect water molecules, water is able to absorb heat without changing its temperature much. The temperature water can both rise and fall, but it does so slowly. Water can be vaporized, but it takes a lot of energy to break the hydrogen bonds in order for it to evaporate. What is actually happening during this process is that heat is dispelled as the water evaporates.

Finally, the density of water can change depending on if it is in liquid, solid, or gas state. Ice is the densest form of water, followed by liquid water, followed by water as a gas. Unlike a lot of other substances, water expands rather than shrinks when it freezes. We know that ice is more dense than liquid water because it will float when placed in water. Because of this fact, it's possible for there to be life underwater.