Download water: esential for life

Biology
Water Pre-Lab
Name: _____________ Period: ___ Date:________
Directions: Read the following paragraphs highlighting the many lifesustaining properties of water. Highlight or underline important
information and complete the magic square at the end
Polarity
Water’s single oxygen atom attracts electrons much more forcefully than either
of its hydrogen atoms. As a result, the electrons tend to be more closely
associated with the oxygen atom, which becomes somewhat negatively
charged. The two hydrogen atoms, which are electron deficient, become
somewhat positively charged.
Molecules that contain an unequal charge distribution, such
as water, are referred to as polar molecules. They possess
distinct positive and negative regions, or poles. In contrast,
nonpolar molecules lack regions of electric charge. It is
easy to recognize nonpolar molecules because they consist
mostly of carbon and hydrogen atoms. Examples of polar
molecules of biological importance are sugars and amino
acids, the building blocks of proteins. Examples of nonpolar
molecules are fats and waxes.
Polar molecules are said to be hydrophilic, or “water-loving.” This means that
they are attracted to water molecules and dissolve easily in water. Nonpolar
molecules are hydrophobic, or “water-fearing.” This means that they are
repelled by water molecules and do not dissolve in water. Since they are
repelled by water, nonpolar molecules can help shape macromolecules (chains
of individual molecules), such as protein.
A common characteristic of polar molecules is their
extensive capacity to form bonds with other polar
molecules because of attraction between opposite
electrical charges. This kind of linkage, called the
hydrogen bond, is formed when oppositely charged parts
of molecules are attracted to each other. Water clearly
illustrates how this attractive force works: water
molecules are drawn together at their oppositely
charged regions when the positively charged H atom is attracted to the
negatively charged O atom.
Glass has a hydrophilic surface that attracts water molecules with
enough force to overcome the pull of gravity. This action is called
capillary action. The property of water molecules to cling to any
hydrophilic substance is called adhesion. Adhesion powers the
Biology
Water Pre-Lab
Name: _____________ Period: ___ Date:________
process of capillary action. Capillary action plays an important role in the
movement of water through the soil.
Just as water molecules cling to hydrophilic surfaces, they cling to one another
by way of hydrogen bonds, a property called cohesion. When present at a
surface, cohesion between molecules creates a film or
layer that resists being separated. This property of water,
called surface tension, permits a water strider to
seemingly defy gravity and walk across the surface of a
pond.
Universal Solvent
One of water’s most important life-sustaining properties is its effectiveness as a
solvent. A solvent is a substance in which another material, the solute,
dissolves by dispersing as individual molecules or ions. The resulting product is
a solution. Most biologically important substances, particularly polar molecules
(such as sugars and amino acids) and ions (such as table salt), are highly
soluble (dissolvable) in water. Since water is so good as a dissolving substance,
it is often referred to as the “universal solvent.”
Specific Heat
On a sunny day, the water in a swimming pool may warm up a degree or two
while the concrete around the pool may become too hot to walk on in your bare
feet. This may seem strange because both the concrete and the water are
being heated by the same source – the sun. This evidence suggests that it
takes more heat to raise the temperature of some substances than it does to
raise the temperature of others. We consider this an illustration of the
substance’s specific heat.
When water is heated, its individual molecules cannot move faster until the
hydrogen bonds among them are broken. Thus, we consider water to have a
high specific heat because it absorbs considerable heat before its temperature
increases markedly. This property of water helps cells to absorb and store heat
and to resist rises in temperature. In turn, cells are able to maintain
homeostasis, or a constant internal environment. Along similar lines, the
oceans are able to do the same for the planet.
Cooling Agent
Not only is water a good heat absorber, it is also an efficient cooling agent.
Again, because of all the hydrogen bonds that have to be broken, water can’t
change from liquid to gas, or evaporate until it is heated at very high
temperatures. When water does evaporate, it takes with it much of the heat it
absorbed. Evaporation can cool an organism or a surface.
Biology
Water Pre-Lab
Name: _____________ Period: ___ Date:________
Magic Square Directions: Each box within the magic square (on the next page) contains a
letter that corresponds to a vocabulary word in the list below. In
each box write the number of the correct definition in the list below.
Then add the rows and columns. If you get all of the definitions
correct, the sum of the rows and columns will add up to the same
number. This is the magic number.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
The magic
number is:
_________
A. polar molecules
1. molecules that possess distinct poles
B. hydrophilic
2. when oppositely charged parts of molecules are
attracted to each other
C. capillary action
3. resulting product of a solvent and solute
D. cohesion
4. attraction of water molecules to each other through
hydrogen bonds
E. solute
5. ability to cool a surface during evaporation
F. high specific heat
6. ability of a molecule to absorb a lot of heat before its
temperature rises
G. adhesion
7. attraction of water molecules to any hydrophilic
substance
H. solvent
8. maintaining constant conditions
I.
9. dissolves a solute
homeostasis
J. nonpolar molecules
10. molecules that lack regions of electric charge
K. hydrophobic
11. repelled by water molecules
L. cooling agent
12. material that dissolves in a solvent
M. surface tension
13. a film or layer at the surface of molecules that resists
being separated
N. solution
14. attraction of water molecules strong enough to
overcome the force of gravity
O. hydrogen bond
15. molecules attracted to water and readily dissolve
P. universal solvent
16. water’s ability to dissolve many substance