Essay/Term paper: Properties of water

Essay, term paper, research paper:  Biology

Properties of Water


Water is essential for life as we know it on earth. It is used by plants
and animals for basic biological processes which would be impossible without the
use of water. The origin of all life can be traced back to the water in the
Earth's precambrien seas. Water is also the universal solvent. It reacts with
more elements and compounds than any other substance known to man.
Water is a polar molecule made up of on atom of hydrogen and two atoms of
oxygen. It is attracted to itself by hydrogen bonds. Hydrogen bonds are weaker
than covalent bonds, but collectively these bonds hold water together and give
it its cohesiveness. These bonds are also very important to water's ability to
absorb heat, as without hydrogen bonds water would have a boiling point of -80
degrees C and a freezing point of -100 degrees C.
In reality, however, water has a boiling point of 100 degrees C and a
freezing point of 0 degrees C. The amount of energy needed to raise the
temperature of one gram of water by one Celsius degree is called a Calorie. One
Calorie is about twice as much energy as you need to warm one gram of most other
fluids by the same amount. This makes water much better for regulating the
temperatures of animals and the environment.
Water also has a very high heat of vaporization. Converting one gram of
cold water into ice requires 80 Calories of energy. Converting the same amount
of very hot water into steam requires 540. The high amounts of energy required
to change water from its liquid state make water tend to stay a fluid. The
process of freezing water involves slowing down the activity of the water
molecules until they contract and enter into a solid state. Once the ice is
cooled down to 4 degrees or less, the hydrogen bonds no longer contract, but
they become rigid and open, and the ice becomes less dense. Because the ice has
become less dense, it floats on liquid water. Water freezes from the top down.
Once the top freezes, it acts as an insulator, so that the water beneath it
takes a very long time to cool off enough that it freezes. This also traps just
enough warmth to keep marine animals alive during the winter.
The process of turning water into steam is a different story. Because it
requires the breaking of water's hydrogen bonds, this process takes far more
energy than it does to turn water into ice. The extra energy that is used in
converting water into steam helps keep the overall temperature from getting too
hot. In this manner water regulates the temperature of both animals when they
sweat, and the earth through evaporation.
Water affects the earth's ecosystems in very important ways as well. When
water in the earth's saltwater bodies evaporates into the air. This water vapor
then cools off, becomes liquid again, and then falls as rain or snow. The salt
is left behind, and the resulting precipitation helps replenish the water in
lakes, streams, rivers, and the groundwater supply. However, all of this water
eventually flows down to the level of the oceans, and the cycle begins again.
Because of this cyclical pattern, water is consided to be a renewable resource.
However, some chemical impurities can remain with the water, even through the
process of evaporation. These remain in the water and cause problems until they
are either filtered out by natural or artificial processes, or until they are
diluted enough that they are no longer a problem. Of all the water on the earth,
only three percent is fresh. Of that three percent, only 1/3 is considered safe
for consumption.
The properties of water give it the ability to react with different
elements and molecules in very interesting ways. Water's properties allow it to
be the focal point of many cellular functions, primarily because of its reactive
abilities.
Ionization is one example of these reactions. This occurs when a water
molecule in a hydrogen bond with another one loses an atom of hydrogen. The
remaining particle is a hydroxl ion. Micromolecules with different charges than
water can cause ionization to happen as well. During the process of ionization
water realeases an eaqual number of hydrogen (H+) and hydroxyl (OH-). This
dissociation process involves only a few water molecules at once. The actual
number is about 10-7 moles/liter).
Acids [L. acidus, sour] are molecules that release the hydrogen ions in
the dissociation process. Strong acids, such as hydrochloric, dissociate almost
entirely in water. Bases are molecules that take up these extra hydrogen ions.
Water passes through pores easily. Cells take advantage of this by
having ³channels² -- tiny holes in the cell membrane. These are exactly the
right size that water can get through them, while larger particles are held
inside.
Osmosis [Gk. Osmo, pushing] is defined by the Sylvia Mader textbook as ³
the diffusion of water across a differentially permeable membrane². This
process is caused by a fluid attempting to seek equilibrium by going from a high
pressure situation into a lower pressure one. This pressure that causes this
operation is known as osmotic pressure.
Another interesting state that water can be in is that of an isotonic
solution. These are solutions which neither water is neither gained nor lost,
and the pressure is equal on both sides of the cell membrane. When this
pressure is not equal, the degree of the inequality is defined as tonicity.
When the pressure is very unequal, so that the pressure causes water to
flow inward, it is known as a hypotonic solution [hypo, less than]. The ³less
than² prefix refers to a solution with a lower percentage of solute, and which
contains more water than the cell. The cell then swells, possibly even to the
point where the cell will burst. These exploded cells are referred to as lysis.
The pressure that caused them to pop in the first place is referred to turgor [L.
turg, swell] pressure.
The opposite state is referred to as a hypertonic solution [hyper, more
than]. The ŒŒmore than² prefix in this word refers to a solution with a higher
level of solute, and the cell contains more water than the outside solution.
Therefore, a cell in a hypertonic solution tends to shrivel up like a grapefruit
in the sun.
Animals regulate the amount of water in their bodies in very individual
ways, each suited for the environment in which they each live. Sharks and fish
are able to live in an environment nearly saturated by salt by having a sort a
immunity to it. Some sharks survive by making their blood as toxic as the
surrounding water.
Certain seaside animals as well have developed ways to keep the salt in
their water from dehydrating them. Some kinds of birds and reptiles have a sort
of nasal salt gland which allows them to excrete the large amounts of salt that
they take in when they drink. Some mammals as well can live in highly saline
environments by making their urine stronger, and having very dry fecal material.
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