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Carbon atoms are the basis of
most molecules that make up living things. Many
carbon-based molecules are large molecules called
polymers that are made of
many smaller, repeating molecules called monomers. There are four main
types of carbon-based molecules in living things.
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Carbohydrates include sugars
and starches, and are often broken down as a source of chemical energy for cells. Some carbohydrates
are part of cell structure, such as cellulose, which makes up plant cell walls.
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Lipids include fats and oils and, like carbohydrates, are often
broken down asa source of chemical energy for cells. One type of lipid, called a
phospholipid, makes up most of all cell membranes.
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Proteins have a large number of structures and functions. Some
proteins are needed for muscle movement; another protein, called
hemoglobin, transports oxygen in blood. Another type of proteins,
called enzymes, speed up chemical reactions in cells.
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Nucleic acids are molecules that store genetic information and build proteins. DNA stores
genetic information in cells, and RNA helps to build the proteins for which DNA
codes.
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1.
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Carbon is unique due to the carbon atom's
A | bonding properties. | C | ionic compounds. | B | six outer unpaired
electrons. | D | hydrogen bonding
strength. |
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2.
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Which category of carbon-based molecules includes sugars and starches?
A | unsaturated fatty acids | C | proteins | B | phospholipids | D | carbohydrates |
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3.
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Fats, oils, and cholesterol are all types of
A | cell membranes. | C | lipids. | B | hormones. | D | fatty acids. |
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4.
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Proteins are composed of which molecules?
A | amino acids | C | monosaccharides | B | fatty acids | D | nucleic acids |
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5.
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DNA and RNA are two types of
A | proteins. | C | lipids. | B | nucleic acids. | D | carbohydrates. |
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6.
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What is unique about carbon?
A | bonding properties | C | properties as a reactant | B | ability to bond
with oxygen | D | properties as an enzyme |
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7.
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Both animal fats and plant oils are made up of
glycerol and
A | phospholipids. | C | polar
molecules. | B | fatty acids. | D | saturated
fats. |
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At the most fundamental level, every process that takes place in an organism depends on
chemical reactions. In a chemical reaction, substances are changed into different substances
by the breaking and forming of chemical bonds. The substances that are present at the start of a
chemical reaction, and are changed by the reaction, are called reactants. The substances that
are formed by a chemical reaction are the products.
Chemical
bonds must be broken in the reactants and new ones must be formed in the products. Energy must be
added to break chemical bonds. In contrast, energy is always released when new bonds form. The amount
of energy needed to break a bond, or the amount of energy released when a bond forms, is called
bond energy.
All chemical reactions require the input of at
least a small amount of energy in order for bonds to break in the reactants and for the reaction to
start. The energy needed to start a chemical reaction is the activation energy. In general,
there are two types of energy changes that can occur during a chemical reaction.
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Exothermic reaction: An exothermic chemical reaction releases more energy than
it absorbs.
The bonds that are broken in the reactants of an exothermic reaction
have a higher bond energy
than the new bonds that form in the products. Energy is
usually released as heat or
light.
• Endothermic reaction: An endothermic chemical reaction absorbs more
energy
than it releases. The bonds that are broken in the reactants of an endothermic
reaction
have a lower bond energy than the new bonds that form in the products.
The energy that is absorbed
makes up for the difference.
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8.
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Chemical reactions change substances into different substances by
A | conserving matter between the substances. | B | breaking and forming
chemical bonds. | C | strengthening electrical charges of substances. | D | changing a solvent
into a solute. |
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9.
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Identify the reactants in the following chemical reaction: 6HO + 6CO  CHO + 6O
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10.
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The double arrows tell you that the following reaction  A | takes place very rapidly. | C | occurs in both
directions. | B | is very unstable. | D | has high bond energies. |
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11.
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What is the term for the amount of energy that needs to be added for a chemical
reaction to start?
A | chemical energy | C | bond energy | B | activation energy | D | reactant energy |
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12.
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Which phrase best describes an exothermic chemical reaction?
A | does not absorb any energy | B | forms products with higher bond energy than
reactants | C | is in a state of equilibrium | D | releases more energy than it
absorbs |
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