The Importance of Water to Life on Earth
The Importance of Water to Life on EarthWater 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 -75øC and a freezing point of -125øC4.
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...
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