Water is the most important substance in our evolution and our daily lives. Without water,
life as we know it would not have been possible. This essay will examine the water molecule
in order to ascertain how it brought about Earth’s thriving ecosystem and how important it
is to us today.
Each water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom (or
the apex of the water molecule) bears a slight electronegative charge while hydrogen
possesses a more positive one1 (figure a). Because opposite charges attract, the water
molecules are drawn together. When an oxygen atom is linked to a neighboring molecule’s
hydrogen atom, a bond called a hydrogen bond is formed2. In an ice crystal the hydrogen
bonds govern the shape of the crystal so that the grid of molecules surrounds relatively
large spaces (imagine figure b in three dimensions). In a liquid form, water has no such
spaces; thus ice is less dense and will float on liquid water. If not for this, great bodies
of water would freeze from the bottom up without the insulation of a top layer of ice and
all life in the water would die.
The water molecule is a very small one but because of its unique properties it behaves like
a larger one. The bonds between water molecules are so strong that water resists changes in
its state (Solid, liquid, gas); thus water has a higher melting point and a higher boiling
point than another molecule of similar size. If water followed the example of other
molecules its size it would have a boiling point of -75C and a freezing point of -125C4.
This would mean that, on Earth, water would be a gas all of the time and life would not be
possible.
When heat is applied to solid water, some hydrogen bonds get so much kinetic energy that
they break and the ice melts. Liquid water does not necessarily have all four hydrogen bonds
present at all times but it must retain some of them5. For any object to penetrate water, it
must be able to break the hydrogen bonds on the surface of the water. These bonds resist
breaking thus forming a “skin” that allows small insects to walk on the surface of the
water. Without the cohesiveness of water, those insects would not have survived.
All plant life on Earth benefits from the ability of water to make a hydrogen bond with
another substance of similar electronegative charge. Cellulose, the substance that makes up
cell walls and paper products, is a hydrophilic substance (“water-loving”)6. It interacts
with water but, unlike other hydrophilic substances, it will not dissolve in it. Cellulose
can form strong hydrogen bonds with water molecules7. This explains why a paper towel will
“wick” water upwards when it comes in contact with it. Each water molecule will make a
hydrogen bond with cellulose and pull another water molecule up from down below and so on.
Without this feature (capillary action8), plants would find it more difficult to transport
water up their stems to the leaves in order to make food through photosynthesis.
Water has a very high heat capacity. Most of the heat introduced to water is used not to set
water molecules in motion (giving them kinetic energy and causing their temperature to
rise), but to move hydrogen atoms around between neighboring oxygen atoms9. If all of this
heat was used solely to warm the water, living cells would boil in their own heat. Every
action in a living cell releases some heat. If the heat was not dissipated by the water, all
living things would cook themselves.
In order for water to evaporate from the surface of liquid water, a certain amount of
energy must be expended to break its hydrogen bonds. Because these hydrogen bonds are so
strong, water requires a lot of heat to boil (100C). When water vaporizes, it takes along
all of the heat energy required to break its bonds thus having a powerful cooling effect on
the original body of water 10. It takes very little water loss to cool water substantially.
If humans had no way of perspiring, their body temperatures would rise about 70C in one
single day11.
Water is very important because it is as close as we can get to a “universal solvent.” When
a crystal of salt is dropped into a glass of water, the water begins to surround the sodium
and chloride atoms in the salt in what is called a hydration sphere12. The atoms interact
with the water molecule and leave the surface of the salt crystal, until the entire crystal
is dissolved. This has two effects: the salt is dissolved and the water molecules are
disturbed. When the water molecules are altered in this fashion they can no longer take part
in the formation of ice crystals13. This is why oceans, which contain a lot of salt, resist
freezing.
In conclusion, it is apparent that water is the most important substance ever to have been
created because it is so vital to our race. Its unique properties aid all living things to
survive in the scheme of nature on our planet Earth.1.Kirk, David L. Biology Today: Third
Edition p. 225 2.Ibid p. 256 3.Ibid p. 256 4.Ibid p. 257-258 5.Ibid p. 256 6.Ibid p. 259
7.Ibid p. 259 8.Ibid p. 259 9.Ibid p. 257 10.Ibid p. 257 11.Ibid p. 257 12.Ibid p. 259
13.Ibid p. 259 Bibliography:
1)Kirk, David L. Biology Today: Third Edition, Random House Publishers, 1980
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