Melanie Corbett
Dr. Sperry
Biology 1610 – sec. 3
Writing Assignment 1
One of the major themes of biology is the distinctive properties of water and how they
make life possible. These distinctive emergent properties include cohesive behavior, an ability to
moderate temperature, expansion upon freezing, and versatility as a solvent. It is necessary to
understand the chemical make-up of water to comprehend these properties and how they work.
It is important to know certain chemical concepts such as chemical bonds, valence,
chemical reactions, and electro-negativity to understand water. Water is made of two hydrogen
molecules and one oxygen molecule. Because oxygen has a valence of two, two hydrogen atoms
(each with a valence of one) are attracted to the oxygen and they form a covalent bond.
However, because oxygen is more electro-negative than hydrogen, it exerts a greater pull on the
electrons than hydrogen causing the shared electrons to stay around oxygen more than the
hydrogen atoms. This gives oxygen a slight negative charge and the hydrogen molecules a slight
positive charge, making water a polar molecule. Because water is polar, it can form a special
type of bond called a hydrogen bond, which is a weak bond between two polar molecules. It is
the polarity of water and its ability to form hydrogen bonds that gives it such unique properties.
A major property of water is the cohesion and adhesion of water molecules. Cohesion
means it is attracted to itself; adhesion means it is attracted to other substances. Water’s polarity
is what causes this cohesion and it is because of this that water can do things like climb up trees.
Also, all the hydrogen bonds water creates are strong when put together, giving water strong
surface tension.
Water is also unique in that it has backwards density. Most things get smaller when they
freeze, but water expands. This is due to the hydrogen bonds that water is forming. In water,
these bonds are scattered and are quickly forming and breaking, making it a liquid. However, in
colder temperatures the molecules slow down and are able to space out and form more structured
hydrogen bonds. It is because of this property that ice can float on water and the earth is not
covered in a frozen ocean. Polar bears use this to float on ice and this also allows fish to survive
underwater when it freezes on top.
One property that is essential for life on earth is water’s ability to moderate temperatures
on earth. Water can do this because it has a high specific heat which means it takes a lot of
energy to break the hydrogen bonds in water. This means water can absorb heat from warmer air
and release it into cooler air. For example, in a coastal area there is not a lot of variance in the
heat throughout the year because all the water in the nearby ocean can absorb the heat. However,
in a desert where there is not a lot of water, temperatures can go from 110oF in the day to 15oF at
night. Another similar property of water is its high heat of vaporization which is the heat energy
needed for 1 g of liquid to be converted to gas. It is this property that lets us humans release heat
through sweating and is the reason why it takes water so long to heat up to boiling.
The final unique property of water is its ability as a solvent. Water can dissolve any polar
substance, such as salt. This property is especially applicable in cells. Cells are surrounded by a
phospholipid bilayer, with hydrophobic (fear of water) tails and hydrophilic (love of water)
heads. This allows a cell to regulate what comes in and out of it and perform all its functions.
This also makes water a good buffer for chemical reactions that can happen inside the cell.
Understanding the chemical structure of water helps one comprehend its unique emergent
properties and how these properties are essential for life on earth. Water’s ability to moderate
temperature, cohesion, backwards density, and its ability to act as a solvent are each essential
characteristics that not only helps large organisms survive but also helps in small structures like
cells.