Remember the levels of
organization of life?
Life: Small Picture to Big Picture
Atoms
• The most abundant
elements in living
organisms are:
Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Why is life carbon-based?
• Carbon can bond and form
stable compounds with a
large number of atoms.
– Carbon can bond with 4
atoms
– Nitrogen can bond with 3
atoms
– Oxygen can bond with 2
atoms
– Hydrogen can bond with 1
atom
• Silicon can also bond with
4 atoms, but compounds
are not as stable.
Abundance of Elements in Life
The 4 most common
elements found in
living things:
Carbon, Hydrogen,
Oxygen, Nitrogen
The 5th and 6th most
common:
Phosphorus and Sulfur
S&P
N
C
O
H
Notice the amount of H and O?
Properties of Water
Molecular Structure of Water
Polarity of Water
These partial charges are very important to the
biochemistry of living things. (Polar things stick to polar
things, nonpolar things stick to nonpolar things.)
How Soap Works
Soap is made up of
molecules that have both
a polar and nonpolar side.
The polar side is attracted
to polar water molecules,
the nonpolar side is
attracted to nonpolar
grease or oil molecules.
The soap ends up
surrounding the grease
with its nonpolar tails all
the way around. The
polar heads facing the
outside are attracted to
water molecules and
wash the surrounded
grease or oil away.
Hydrogen Bonding
• The partial charges of
the oxygens and
hydrogens between
water molecules
attract each other.
• The resulting bond is
very weak. It’s called
a hydrogen bond.
• H-bonds are very
important in Biology.
H-bond
Hydrogen-Bonding
Hydrogen Bonding
Cohesion & Surface Tension
H-bonds are the
reason water forms
drops, and can hold
up a water strider.
Cohesion & Surface Tension
• Cohesion: the attraction between water molecules
due to H-bonds. This results in water’s ability to
form drops, instead of staying in separated
droplets.
• Surface Tension: This is also a result of cohesion.
The combined strength of all the H-bonds between
water molecules in a pool causes a film or surface
that is slightly resistant, sticky, and supportive.
Adhesion
• The partial charges on water molecules can
also form H-bonds with other molecules.
Usually these molecules are also polar, or
charged.
Capillary Action
• Plants and trees are
able to get water to
their branches and
leaves from their roots
using capillary
action.
• Capillary action is an
effect caused by the
combination of both
cohesion & adhesion.
Specific Heat of Water
• Water has a high specific
heat capacity.
• It takes a lot more heat
energy to increase the
temperature of water by 1
C than it does for alcohol
or iron!
• This is why organisms can
stay out in the hot or cold
for a duration of time.
Water helps to regulate
and stabilize body
temperature.
Water Trivia
• What percentage of your body is water?
• A: Your body contains as much as 60% water.
Men have more water in their bodies than women,
because women have more body fat.
• What percentage of the Earth’s surface is
water?
• A: Water covers about 70% of the Earth. 98% of
that water is found in the oceans.
Water Trivia
• Is it possible to die from drinking too much
water?
• A: Yes. Too much water causes all of your body’s
cells and tissues to swell. Fluid can flow into your
lungs, you will act intoxicated, and eventually
may suffer seizures and die. “Water intoxication”
is more likely to occur if you drink a lot of water
in a short period of time.