s8pe-31102-ca
12/9/05
5:02 PM
MAZER
Page 345
KEY CONCEPT
Carbon-based molecules
have many structures.
CALIFORNIA
Content Standards
8.3.c Students know
that compounds are
formed by combining
two or more different
elements and that
compounds have properties that are different
from their constituent
elements.
8.6.a Students know
that carbon, because
of its ability to combine in many ways
with itself and other
elements, has a central
role in the chemistry
of living organisms.
VOCABULARY
organic compound p. 345
inorganic compound
p. 346
polymer p.348
isomer p. 350
VOCABULARY
Remember to make a
magnet word diagram for
organic compound and for
other vocabulary terms.
BEFORE, you learned
NOW, you will learn
• A few basic elements make
up all living things
• Atoms of one element differ
from atoms of other elements
• Life on Earth is based on carbon
• About the importance of
carbon in living things
• Why carbon can form many
different compounds
• About different structures of
carbon-based molecules
THINK ABOUT
Where can you find carbon?
The wood of a pencil consists of carbon-based
molecules. These molecules are considered to be
organic. The graphite in the center of the pencil is
also made of carbon. In fact, graphite is pure
carbon, but it is not considered to be organic.
What makes the carbon in wood different from
the carbon in graphite?
Living and nonliving things contain carbon.
In the previous section, you learned that life on Earth is based on
carbon. Carbon may not be the most abundant element in living
things, but it certainly is the most important.
At one time, scientists thought that the chemical reactions that
took place inside of living things could not occur outside of them.
The carbon molecules were so complex, scientists thought they must
have been made in some unknown ways. They therefore called compounds based on carbon organic compounds. Notice the similarity
between the words organic and organism. Here on earth, living things
contain carbon.
Of course, scientists eventually realized that the reactions
occurring inside the body could occur outside it as well. They even
found they could make some of the very complex carbon compounds
found in the body. They learned that carbon’s importance in living
things comes from its ability to bond with other atoms in different
ways. As you will see in this section, carbon is an atomic acrobat.
Chapter 11: Chemistry of Living Systems 345
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