Bio07_TR_U01_CH02.

QXD 4/28/06 3:28 PM Page 59

Name______________________________ Class __________________ Date ______________

Chapter 2 The Chemistry of Life

Summary
2–1 The Nature of Matter 2–2 Properties of Water
The basic unit of matter is the atom. The The water molecule (H2O) is neutral. Yet, the
subatomic particles that make up atoms are oxygen end of the molecule has a slight posi-
protons, neutrons, and electrons. Protons tive charge, and the hydrogen end has a
and neutrons have about the same mass. slight negative charge.
Protons are positively charged particles (+), A molecule in which the charges are
and neutrons carry no charge. Protons and unevenly distributed is called a polar
neutrons together form the nucleus, at the molecule. Polar molecules can attract each
center of the atom. The electron is a nega- other. The attraction between the hydrogen
tively charged particle (–). Atoms have atom on one water molecule and the oxygen
equal numbers of electrons and protons, atom on another water molecule is called a
and therefore atoms do not have a charge. hydrogen bond. Cohesion is an attraction
A chemical element is a pure substance between molecules of the same substance.
that consists entirely of one type of atom. Adhesion is an attraction between molecules
The number of protons in an atom of an ele- of different substances.
ment is the element’s atomic number. A mixture is a material composed of two
Atoms of an element can have different or more elements or compounds that are
numbers of neutrons. Atoms of the same physically mixed together—the substances
element that differ in the number of neu- are not chemically combined. A solution is a
trons they contain are known as isotopes. mixture in which all the components are
Because all the isotopes of an element have evenly distributed throughout the mixture.
the same number of electrons, they all have In a solution, the substance that is dissolved
the same chemical properties. is called the solute. The substance in which
A chemical compound is a substance the solute dissolves is called the solvent.
formed by the chemical combination of two Water is the greatest solvent on Earth.
or more elements in definite proportions. A water molecule can react to form ions.
Atoms in compounds are held together by A water molecule (H2O) can form a hydro-
_
chemical bonds. An ionic bond is formed gen ion (H+) and a hydroxide ion (OH ). The
when one or more electrons are transferred pH scale indicates the concentration of H+
from one atom to another. A covalent bond ions in a solution. Pure water has a pH of 7.
forms when electrons are shared between An acid is any compound that forms H+
atoms. The structure that results when ions in solution. Acidic solutions contain
atoms are joined together by covalent bonds higher concentrations of H+ ions than pure
is called a molecule. Unequal sharing of water. A base is a compound that produces
_
electrons creates regions of positive and OH ions in solution. Basic, or alkaline,
negative charges in molecules. Slight attrac- solutions contain lower concentrations of
tion can develop between the oppositely H+ ions than pure water and have pH val-
charged regions of nearby molecules. Such ues above 7.
intermolecular forces of attraction are called
van der Waals forces.

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

59
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 60

Name______________________________ Class __________________ Date ______________

2–3 Carbon Compounds Proteins contain nitrogen as well as car-

Organic chemistry is the study of all com- bon, hydrogen, and oxygen. Proteins are
pounds that contain bonds between carbon polymers of molecules called amino acids.
atoms. Carbon compounds are also called Some proteins control the rate of reactions
organic compounds. Many of the molecules and regulate cell processes. Some are used
in living things are so large that they are to form bones and muscles. Others trans-
known as macromolecules. Macromolecules port substances into or out of cells or help
are formed in a process called polymerization. to fight disease.
Smaller units, called monomers, join together
to form macromolecules, or polymers. 2–4 Chemical Reactions and
Four groups of organic compounds Enzymes
found in living things are carbohydrates, A chemical reaction is a process that
lipids, nucleic acids, and proteins. Carbohy- changes one set of chemicals (reactants) into
drates are compounds made up of carbon, another set of chemicals (products). Chemi-
hydrogen, and oxygen atoms. Living things cal reactions always involve the breaking of
use carbohydrates as their main source of bonds in reactants and the formation of new
energy. Plants and some animals use carbo- bonds in products.
hydrates in structures. Starches and sugars Some chemical reactions release energy,
are examples of carbohydrates. and other reactions absorb energy. Chemical
Lipids are made mostly from carbon and reactions that release energy often occur
hydrogen atoms. Fats, oils, and waxes are spontaneously. Every chemical reaction
lipids. Lipids are used in living things to needs energy to get started, and that starting
store energy. Some lipids are important parts energy is called activation energy.
of biological membranes and waterproof A catalyst is a substance that speeds up
coverings. Lipid molecules are made up of the rate of a chemical reaction. Catalysts
compounds called fatty acids and glycerol. work by lowering a reaction’s activation
Nucleic acids contain hydrogen, oxy- energy. Enzymes are proteins that act as bio-
gen, nitrogen, carbon, and phosphorus. logical catalysts. Enzymes speed up chemical
Nucleotides are the monomers that make reactions by lowering activation energies. In
up nucleic acids. Each nucleotide consists an enzyme-catalyzed reaction, the reactants
of a 5-carbon sugar, a phosphate group, are known as substrates. The substrates bind
and a nitrogenous base. Nucleic acids store to a site on the enzyme called the active site.
and transmit hereditary, or genetic, infor-
mation. There are two kinds of nucleic
acids: ribonucleic acid (RNA) and deoxyri-
bonucleic acid (DNA).

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

60
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 61

Name______________________________ Class __________________ Date ______________

Chapter 2 The Chemistry of Life

Section 2–1 The Nature of Matter (pages 35–39)

Key Concepts
• What three subatomic particles make up atoms?
• How are all of the isotopes of an element similar?
• What are the two main types of chemical bonds?

Atoms (page 35)

1. The basic unit of matter is called a(an) .

2. Describe the nucleus of an atom.

3. Complete the table about subatomic particles.

SUBATOMIC PARTICLES

Particle Charge Location in Atom

Positive

Neutral

Negative

4. Why are atoms neutral despite having charged particles?

Elements and Isotopes (page 36)

5. What is a chemical element?

6. What does an element’s atomic number represent?

7. Atoms of the same element that differ in the number of neutrons they contain are
known as .
8. How are isotopes identified?
9. Why do all isotopes of an element have the same chemical properties?

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

61
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 62

Name______________________________ Class __________________ Date ______________

Chemical Compounds (page 37)

10. What is a chemical compound?

11. What does the formula for table salt indicate about that compound?

Chemical Bonds (pages 38–39)

12. What holds atoms in compounds together?
13. Complete the table about the main types of chemical bonds.
CHEMICAL BONDS

Type Formed when . . .

Covalent bond

Ionic bond

14. What is an ion?

15. Is the following sentence true or false? An atom that loses electrons has a negative
charge.
16. The structure that results when atoms are joined together by covalent bonds is called
a(an) .
17. Circle the letter of each sentence that is true about covalent bonds.
a. When atoms share two electrons, it is called a double bond.
b. In a water molecule, each hydrogen atom forms a single
covalent bond.
c. Atoms can share six electrons and form a triple bond.
d. In a covalent bond, atoms share electrons.
18. The slight attractions that develop between oppositely charged regions of nearby
molecules are called .

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

62
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 63

Name______________________________ Class __________________ Date ______________

Section 2–2 Properties of Water (pages 40–43)

Key Concepts
• Why are water molecules polar?
• What are acidic solutions? What are basic solutions?

The Water Molecule (pages 40–41)

1. Is the following sentence true or false? A water molecule is neutral.
2. Why is a water molecule polar?

3. Circle the letter of each sentence that is true about hydrogen bonds.
a. A hydrogen bond is stronger than an ionic bond.
b. The attraction between the hydrogen atom on one water
molecule and the oxygen atom on another water molecule is an
example.
c. A hydrogen bond is stronger than a covalent bond.
d. They are the strongest bonds that form between molecules.
4. Complete the table about forms of attraction.

FORMS OF ATTRACTION

Form of Attraction Definition

Cohesion

Adhesion

Solutions and Suspensions (pages 41–42)

5. What is a mixture?

6. A mixture of two or more substances in which the molecules of the substances are
evenly mixed is called a(an) .
7. The greatest solvent in the world is .
8. What is a suspension?

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

63
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 64

Name______________________________ Class __________________ Date ______________

9. Complete the table about substances in solutions.

SUBSTANCES IN SOLUTIONS

Substance Definition Saltwater Solution

Solute

Water

Acids, Bases, and pH (pages 42–43)

10. Why is water neutral despite the production of hydrogen ions and hydroxide ions?

11. What does the pH scale indicate?

12. On the pH scale below, indicate which direction is increasingly acidic and which is
increasingly basic.

Neutral

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Stomach acid

Lemon juice

Normal rainfall

Pure water
Human blood

Seawater

Soap

Bleach

13. How many more H+ ions does a solution with a pH of 4 have than a solution with a
pH of 5?
14. What is an acid?
15. Is the following sentence true or false? Strong bases have pH values ranging from
11 to 14.
16. What are buffers?

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

64
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 65

Name______________________________ Class __________________ Date ______________

Section 2–3 Carbon Compounds (pages 44–48)

Key Concept
• What are the functions of each group of organic compounds?

The Chemistry of Carbon (page 44)

1. How many valence electrons does each carbon atom have?

2. What gives carbon the ability to form chains that are almost unlimited in length?

Macromolecules (page 45)

3. Many of the molecules in living cells are so large that they are known as
.
4. What is the process called by which macromolecules are formed?
5. When monomers join together, what do they form?
6. What are four groups of organic compounds found in living things?
a.
b.
c.
d.

Carbohydrates (pages 45–46)

7. What atoms make up carbohydrates?

8. Circle the letter of each sentence that is true about carbohydrates.

a. Starches and sugars are examples of carbohydrates.
b. Living things use them as their main source of energy.
c. The monomers in sugar polymers are starch molecules.
d. Plants and some animals use them for strength and rigidity.
9. Single sugar molecules are also called .
10. Circle the letter of each monosaccharide.
a. galactose c. glucose
b. glycogen d. fructose

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

65
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 66

Name______________________________ Class __________________ Date ______________

11. What are polysaccharides?

12. How do plants and animals store excess sugar?

Lipids (pages 46–47)

13. What kinds of atoms are lipids mostly made of?

14. What are three common categories of lipids?

a. b. c.
15. Many lipids are formed when a glycerol molecule combines with compounds
called .
16. Circle the letter of each way that fats are used in living things.
a. As parts of biological membranes
b. To store energy
c. To give plants rigidity
d. As chemical messengers
17. Complete the table about lipids.

LIPIDS

Kind of Lipid Description

Each carbon atom in a lipid’s fatty acid chain is joined to another

carbon atom by a single bond.

Unsaturated

A lipid’s fatty acids contain more than one double bond.

Nucleic Acids (page 47)

18. Nucleic acids contain what kinds of atoms?

19. The monomers that make up nucleic acids are known as .

20. A nucleotide consists of what three parts?

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

66
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 67

Name______________________________ Class __________________ Date ______________

21. What is the function of nucleic acids in living things?

22. What are two kinds of nucleic acids?

a.
b.

Proteins (pages 47–48)

23. Proteins contain what kinds of atoms?

24. Proteins are polymers of molecules called .

25. What are four roles that proteins play in living things?
a.
b.
c.
d.

Reading Skill Practice

You can often increase your understanding of what you’ve read by making
comparisons. A compare-and-contrast table helps you to do this. On a separate sheet
of paper, make a table to compare the four groups of organic compounds you read
about in Section 2–3. You might use the heads Elements, Functions, and Examples
for your table. For more information about compare-and-contrast tables, see
Organizing Information in Appendix A.

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

67
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 68

Name______________________________ Class __________________ Date ______________

Section 2–4 Chemical Reactions and Enzymes (pages 49–53)

Key Concepts
• What happens to chemical bonds during chemical reactions?
• How do energy changes affect whether a chemical reaction will occur?
• Why are enzymes important to living things?

Chemical Reactions (page 49)

1. What is a chemical reaction?

2. In the space provided, write a definition for each of the terms

Definition

Reactants

Products

3. Chemical reactions always involve changes in chemical .

Energy in Reactions (page 50)

4. What is released or absorbed whenever chemical bonds form or are broken?

5. What do chemical reactions that absorb energy need to occur?

6. Chemists call the energy needed to get a reaction started the .

7. Complete the graph of an energy-releasing reaction by indicating where the energy of
the reactants, the energy of the products, and the activation energy should appear.

Energy-Releasing Reaction
Energy

Course of Reaction

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

68
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 69

Name______________________________ Class __________________ Date ______________

Enzymes (pages 51–52)

8. What is a catalyst?

9. Proteins that act as biological catalysts are called .

10. What do enzymes do?

11. What is part of an enzyme’s name usually derived from?

Enzyme Action (pages 52–53)

12. The reactants of enzyme-catalyzed reactions are known as .
13. Why are the active site and the substrates in an enzyme-catalyzed
reaction often compared to a lock and key?

14. The binding together of an enzyme and a substrate forms a(an)

.
15. How do most cells regulate the activity of enzymes?

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

69
Bio07_TR_U01_CH02.QXD 4/28/06 3:28 PM Page 70

Name______________________________ Class __________________ Date ______________

Chapter 2 The Chemistry of Life

Vocabulary Review
Crossword Puzzle Use the clues below to fill in the spaces in the puzzle with the correct words.
Across Down
1. element or compound that enters into a 2. negatively charged subatomic particle
chemical reaction 3. compound that produces hydroxide
4. process that changes one set of chemi- ions in solution
cals into another 5. bond formed when one or more elec-
7. positively charged subatomic particle trons are transferred from one atom to
8. substance formed by the chemical com- another
bination of two or more elements in 6. monomer of nucleic acid
definite proportions 9. monomer of protein
11. positively or negatively charged atom 10. compound that forms hydrogen ions in
12. carbon compound that stores and trans- solution
mits genetic information 13. atom of same element that differs in
14. the center of an atom number of neutrons compared with
16. bond formed when electrons are shared other atoms of the element
between atoms 15. basic unit of matter
17. macromolecule formed when
monomers join together

1 2

4 5 6

10

11 12

13

14

15

16

17

© Pearson Education, Inc., publishing as Pearson Prentice Hall.

70