Exploring Life
Chapter 4+ 5 Study Guide
4.1 Life Requires about 25 chemical
elements
4.2 Skip
4.3 skip
4.4 Life Depends on the unique
properties of water
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4.1 Life Requires about
25 chemical elements
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Why is there chemistry in a biology
textbook?
The answer is that all of biology
involves chemistry.
All living things share the same
chemical building blocks and depend
on chemical processes for survival.
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4.1 Life Requires about
25 chemical elements
Elements- About 25 elements
are essential to life .
 of these elements
oxygen (O), carbon (C),
hydrogen (H),
and nitrogen (N)—
make up about
96 percent of your body.

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4.4 Life Depends on the unique
properties of water
• All living things are dependent on
water.
• Inside your body, your cells are
surrounded by a fluid that is mostly
water, and your cells themselves are
70 to 95 percent water
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4.4 Life Depends on the unique properties of water
• The tendency of molecules of the same kind to
stick to one another is called cohesion.
• Cohesion is much stronger for water than for
most other liquids.
• Water molecules are
also attracted to
certain other molecules.
This is called adhesion
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4.4 Life Depends on the unique properties of water
• Trees depend on
cohesion and adhesion
to help transport water
from their roots to
their leaves
• This effect is known
as surface tension.
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4.4 Life Depends on the unique properties of
water
• You've witnessed another example of
cohesion if you've ever seen an insect
"skating" across the surface of a pond.
• This
effect is an example
of surface tension,
also
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4.4 Life Depends on the unique properties of
water
• Temperature Moderation
If you have ever burned your finger on a
metal pot while waiting for the water in it
to boil, you know that water heats up much
more slowly than metal.
In fact, because of hydrogen bonding,
water has a better ability to
resist temperature change
than most other substances
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4.4 Life Depends on the unique properties of
water
• One result of this property (temperature moderation) is
that it causes oceans and large lakes to moderate the
temperatures of nearby land areas
• Water also moderates
• temperature through evaporation,
• such as when you sweat.
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4.4 Life Depends on the unique properties of
water
• Ice floats because its molecules are less densely
packed than those in liquid water.
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4.4 Life Depends on the unique properties of water
• How is the fact that ice floats important to living
things?
• If ice sank, it would form on the bottom of a body of
water as the water was cooling.
• Ponds and lakes would freeze from the bottom up,
trapping the fish and other organisms in a shrinking
layer of water without access to the nutrients from the
muddy bottom.
• Instead, when a deep body of water cools,
• the floating ice insulates the liquid water below, allowing
life to persist under the frozen surface.
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4.4 Life Depends on the unique properties of water
• Water is the main solvent inside all cells,
• in blood,
• and in plant sap.
• Water dissolves an enormous variety of solutes
necessary for life.
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4.4 Life Depends on the unique properties of water
• Acids, Bases, and pH
pH of 7 is neither
acidic nor basic.
The pH of the
solution inside
most living cells
is close to 7.
Which is the most acidic?
Which is the most basic?
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4.4 Life Depends on the unique properties of water
• Buffers
• Because the molecules in cells are very sensitive
to concentrations of H+ and OH- ions, even a
slight change in pH can be harmful to
organisms.
• Many biological fluids contain buffers,
substances that cause a solution to resist changes
in pH.
• Blood contains buffers (like a sponge or barrier) so
cells stay at pH 7.4
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4.4 Life Depends on the unique properties of
water
•
•
•
•
•
Earth is perfect planet for Life
Contains water
Just far enough and close enough to sun
Just enough energy and heat
Ozone shields harmful radiation
• Essential elements in rock, soil, air
• H, O, C are recycled
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Chapter 5
5.1
 5.2
 5.3
 5.4
 5.5

Organic compounds
Carbohydrates
Lipids
Proteins
Enzymes
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5.1 Organic Compounds
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Carbon
Carbon can form bonds with one or more other
carbon atoms, producing an endless variety of
carbon skeletons.
Most carbon-based molecules are classified as
organic molecules
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Building Organic Compounds
To build compounds
A water molecule
is released
This is called
a dehydration reaction
because it involves
removing (de-) water (hydro-).
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Breaking Down Compounds
In a Hydrolysis reaction,
water (hydro-) is used
to break down
(-lysis) compounds.
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To summarize, water is removed to build a
compound, and water is added to break it down.
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5.2 Carbohydrates
A carbohydrate is an organic
compound made up of sugar
molecules.
Sugars contain the elements carbon,
hydrogen, and oxygen in the ratio of 1
carbon: 2 hydrogen: 1 oxygen (CH2O)
Monosaccharides –simple sugar
(Glucose, fructose, and galactose )
Disaccharides -2 sugars (sucrose)
Polysaccharides--chain of sugars
(Glycogen, cellulose, and starch )
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5.3 Lipids
Oil's inability to mix with water is
typical of the class of water-avoiding
compounds called lipids
 A fat consists of a three-carbon
backbone
saturated fat

unsaturated fat
Steroids-hormones and cholesterol
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5.4 Proteins
A protein is a polymer constructed from
a set of just 20 kinds of amino acids
 Made up of C, H, O, N-Put this in your
notes
 Cells create proteins by linking amino
acids together into
a chain called a polypeptide

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5.5 Enzymes
• To start a chemical reaction, it is first
necessary to weaken chemical bonds.
This activation process requires that
the molecules absorb energy. This
"start-up" energy is called activation
energy
• The main catalysts of chemical
reactions in organisms
are specialized proteins
called enzymes
• Enzymes provide a way for reactions to 23
The enzyme sucrase,
which catalyzes
the hydrolysis (breakdown)
of sucrose (the substrate).
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pH and temperature can affect how an
enzyme works or if it can work at all
Enzymes are specific
Enzymes can be re-used
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Organic compound and
Function Chart
Functions
Structural
Enzymatic
Organic Compound
Storage
Energy
Material
Carbohydrate
X
X
x
Lipids
X
x
x
Proteins
x
Nucleic Acids
x
x
Information
X
x
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• Video (Chemistry of Life 18 min)
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