Raven/Johnson Biology 8e
Chapter 03– Answers
1. How is a polymer formed from multiple monomers?
a. From the growth of the chain of carbon atoms
b. By the removal of an –OH group and a hydrogen atom
c. By the addition of an –OH group and a hydrogen atom
d. Through hydrogen bonding
The correct answer is b—
A. Answer a is incorrect. The addition of carbon atoms to a molecule is a consequence of the
formation of a polymer, but it does not describe how a polymer is formed.
The correct answer is b—By the removal of an –OH group and a hydrogen atom
B. Answer b is correct. The growth of complex biological molecules occurs through
condensation or dehydration reactions that form covalent bonds between monomers by
the removal of a molecule of water (H2O, or OH + H).
The correct answer is b—
C. Answer c is incorrect. The addition of –OH and H, in other words, H2O to a covalent
bond is a process called hydrolysis. Hydrolysis reactions break covalent bonds and
therefore break up polymers.
The correct answer is b—
D. Answer d is incorrect. Hydrogen bonds are important for stabilizing molecules, but
covalent bonds are what are required to build polymers from monomers.
2. Why are carbohydrates an important molecule for energy storage?
a. The C–H bonds found in carbohydrates store energy.
b. The double bond between carbon and oxygen are very strong.
c. The electronegativity of the oxygen atoms means that a carbohydrate is made up
of many polar bonds.
d. They can form ring structures in the aqueous environment of a cell.
The correct answer is a—The C–H bonds found in carbohydrates store energy.
A. The C–H bonds are nonpolar (review chapter 2) and therefore have high potential energy
The correct answer is a—
B. Answer b is incorrect. Double bonds are strong covalent bonds, however C=O bonds only
exist in the linear forms of carbohydrate molecules. The ring form of carbohydrates is
more common in biological systems.
The correct answer is a—
C. Answer c is incorrect. Oxygen is an electronegative atom and the bonds between oxygen
and hydrogen are polar (allowing carbohydrates to interact with water). However, polar
bonds are not good at storing energy.
The correct answer is a—
D. Answer d is incorrect. The ability to form ring structures does not influence the ability of
carbohydrates to store energy. The energy is stored in the C–H bond.
Raven/Johnson Biology 8e
Chapter 03– Answers
3. Plant cells store energy in the form of _________, and animal cells store energy in the
form of ___________
a. fructose; glucose
b. disaccharides; monosaccharides
c. cellulose; chitin
d. starch; glycogen
The correct answer is d—
A. Answer a is incorrect. Fructose and glucose are structural isomers of each other. These
monomers can be used as energy by the cell, but they do not store energy inside cells.
The correct answer is d—
B. Answer b is incorrect. Monosaccharide is the name given to the monomer unit of a
carbohydrate. A disaccharide is formed when two monosaccharides become linked
through a covalent bond. Disaccharides are used for transporting carbohydrates, not
storage.
The correct answer is d—
C. Answer c is not correct. Cellulose forms the cell walls of plant cells, and chitin forms the
cell walls of animal cells. Cell walls provide structural support to cells, but do not store
energy.
The correct answer is d—starch; glycogen
D. Answer d is correct. Starches are large, branched polymers of glucose that store energy
for plants. Likewise, glycogen is a glucose polymer that is stored for energy use by
animal cells.
4. Which carbohydrate would you find as part of a molecule of RNA?
a. Galactose
b. Deoxyribose
c. Ribose
d. Glucose
The correct answer is c—
A. Answer a is incorrect. Galactose is a six-carbon sugar that is a stereoisomer of glucose.
The correct answer is c—
B. Answer b is incorrect. Deoxyribose is found in DNA, not RNA.
The correct answer is c—Ribose
C. Answer c is correct. Ribose is the five-carbon sugar that is part of the nucleotides that
make up RNA.
The correct answer is c—
D. Answer d is incorrect. Glucose is a general name for any five-carbon sugar. This term is
too general to correctly answer this question.
5. What makes cellulose different from starch?
a. Starch is produced by plant cells, and cellulose is produced by animal cells.
Raven/Johnson Biology 8e
Chapter 03– Answers
b. Cellulose forms long filaments, and starch is highly branched.
c. Starch is insoluble, and cellulose is soluble.
d. All of the above.
The correct answer is b—
A. Answer a is incorrect. Both starch and cellulose are the products of plant cells.
The correct answer is b— Cellulose forms long filaments, and starch is highly branched.
B. Answer b is correct. Cellulose filaments are long, unbranched polymers of glucose. These
straight fibers assemble to give strength to the cell walls of plants. Starch is a highly
branched glucose polymer that functions to store energy for plant cells.
The correct answer is b—
C. Answer c is incorrect. If cellulose was soluble, then plant cell walls would not exist.
The correct answer is b—
D. Answer d is incorrect. Answers a and c are also incorrect.
6. A molecule of DNA or RNA is a polymer of—
a. monosaccharides
b. nucleotides
c. amino acids
d. fatty acids
The correct answer is b—
A. Answer a is incorrect. Monosaccharides are the monomer form of a carbohydrate.
The correct answer is b—nucleotides
B. Answer b is correct. Nucleotides are the monomers of nucleic acids. They are composed
of a ribose sugar, nitrogenous base, and a phosphate group.
The correct answer is b—
C. Answer c is incorrect. Amino acids are the monomers that make up proteins
The correct answer is b—
D. Answer d is incorrect. Fatty acids are lipid molecules.
7. What chemical bond is responsible for linking amino acids together to form a protein?
a. Phosphodiester
b. ß-1,4 linkage
c. Peptide
d. Hydrogen
The correct answer is c—
A. Answer a is incorrect. A phosphodiester bond is found linking the nucleotides that form
nucleic acids.
The correct answer is c—
Raven/Johnson Biology 8e
Chapter 03– Answers
B. Answer b is incorrect. A ß-1,4 linkage is found in carbohydrate polymers such as
cellulose.
The correct answer is c—Peptide
C. Answer c is correct. Peptide bonds are the covalent bonds between amino acids.
The correct answer is c—
D. Answer d is incorrect. Hydrogen bonds contribute to the structure of proteins, but are not
involved in holding the individual amino acids together.
8. The double helix structure of a molecule of DNA is stabilized b—
a. phosphodiester bonds
b. peptide bonds
c. an α helix
d. hydrogen bonds
The correct answer is d—
A. Answer a is incorrect. Phosphodiester bonds are responsible for maintaining the sugar–
phosphate backbone of the DNA molecule, but they are not involved in stabilizing the
double helix.
The correct answer is d—
B. Answer b is incorrect. Peptide bonds are the covalent bonds responsible for linking amino
acids together to form proteins.
The correct answer is d—
C. Answer c is incorrect. Don’t be fooled by the word “helix”! An α helix is a form of
protein structure and has nothing to do with DNA. Answer c is not correct.
The correct answer is d—hydrogen bonds
D. Answer d is correct. Hydrogen bonds are formed between the nitrogenous bases of the
two strands of DNA. It is the hydrogen bond formation between A:T and G:C that hold
the DNA together.
9. Which of the following is NOT a difference between DNA and RNA?
a. Deoxyribose sugar versus ribose sugar
b. Thymine versus uracil
c. Double stranded versus single stranded
d. Phosphodiester versus hydrogen bonds
The correct answer is d—
A. Answer a is incorrect. The “D” in DNA stands for deoxyribose and the “R” in RNA
stands for ribose.
The correct answer is d—
B. Answer b is incorrect. DNA and RNA differ in one nucleotide. DNA uses thymine, but
RNA uses uracil.
The correct answer is d—
Raven/Johnson Biology 8e
Chapter 03– Answers
C. Answer c is incorrect. DNA is made up of two strands of nucleic acid polymer while
RNA is only made of one strand.
The correct answer is d—Phosphodiester versus hydrogen bond
D. Answer d is correct. Both DNA and RNA rely on the presence of phosphodiester bonds to
hold the sugar–phosphate backbone of the polymer together. The double strands that
make up a molecule of DNA are held together by hydrogen bonds. However, even though
RNA is a single-stranded molecule, it can fold back onto itself—a property that is
stabilized by hydrogen bonds.
10. What monomers make up a protein?
a. Monosaccharides
b. Nucleotides
c. Amino acids
d. Fatty acids
The correct answer is c—
A. Answer a is incorrect. Monosaccharides are the monomer units of carbohydrates.
The correct answer is c—
B. Answer b is incorrect. Nucleotides are the monomer units of nucleic acids like DNA and
RNA.
The correct answer is c—Amino acids
C. Amino acids with their variable R-groups are the monomers used to form proteins.
The correct answer is c—
D. Answer d is incorrect. Fatty acids are found in lipids.
11. Which part of an amino acid has the greatest influence on the overall structure of a
protein?
a. The (–NH2) amino group
b. The R-group
c. The (–COOH) carboxyl group
d. Both a and c
The correct answer is b—
A. Answer a is incorrect. The amino group of the amino acid participates in the formation of
the peptide bond, but does not influence the overall structure of the protein.
The correct answer is b—The R-group
B. Answer b is correct. The R-group is the variable part of an amino acid. Some R-groups
are polar and hydrophilic. Other R-groups are nonpolar and hydrophobic. Some R-groups
are large and others are small. The combination of these factors leads to differences in the
shape of proteins.
The correct answer is b—
C. Answer c is incorrect. The carboxyl group of the amino acid participates in the formation
of the covalent peptide bond, but is not involved in protein structure beyond this level.
Raven/Johnson Biology 8e
Chapter 03– Answers
The correct answer is b—
D. Answer d is incorrect. The amino and carboxyl groups of an amino acid are the key
functional groups involved in peptide bond formation, but are less influential than Rgroups in determining protein shape.
12. A mutation that alters a single amino acid within a protein can alter—
a. the primary level of protein structure
b. the secondary level of protein structure
c. the tertiary level of protein structure
d. all of the above
The correct answer is d—
A. Answer a is incorrect. Although changing an amino acid does change the primary
sequence, this is not the only effect.
The correct answer is d—
B. Answer b is incorrect. Although changing an amino acid could alter a region of secondary
structure, this is not the only effect.
The correct answer is d—
C. Answer c is incorrect. The tertiary level of protein structure is dependent on the secondary
and primary levels of protein structure. Changing one level influences all levels.
The correct answer is d—all of the above
D. Answer d is correct. The levels of protein structure are all interrelated. The alteration of a
single amino acid represents a change in the primary level of protein structure. This one
change can alter the ability of the protein to form α helices or β-pleated sheets. The
change in secondary structure is then reflected in the three-dimensional, or tertiary, level
of the protein.
13. Which of these factors contributes to the diversity of protein form and function in the
cell?
a. Quaternary interactions between peptides
b. Formation of α helices and ß-pleated sheets
c. The linear sequence of amino acids that makes up the polymer
d. All of the above
The correct answer is d—
A. Answer a is incorrect. Quaternary interactions contribute to the diversity of protein forms
by allowing for the formation of functional aggregates of distinct proteins. However, this
is not the only factor that is important.
The correct answer is d—
B. Answer b is incorrect. The formation of α helices and ß-pleated sheets contributes to the
overall shape of the protein and in that way contributes to both form and function of the
protein, but this is not the only factor.
The correct answer is d—
Raven/Johnson Biology 8e
Chapter 03– Answers
C. Answer c is incorrect. The linear sequence of the amino acids that makes up a protein is a
critical property that determines the folding of the protein through the relative position of
the various R-groups. Shape is a critical property that determines protein function, but it is
not the only factor.
The correct answer is d—All of the above
D. Answer d is correct. All of the properties listed in answers a through d are important
factors that will determine the size and shape, and therefore the form and function, of a
protein.
14. What chemical property of lipids accounts for their insolubility in water?
a. The length of the carbon chain
b. The large number of nonpolar C–H bonds
c. The branching of saturated fatty acids
d. The C=C bonds found in unsaturated fatty acids
The correct answer is b—
A. Answer a is incorrect. The overall length of the carbon chain is not a factor in the ability
of any molecule to interact with water. The ability to dissolve in water is a consequence
of the ability of a molecule to form hydrogen bonds with water molecules. Carbon is not
involved in hydrogen bond formation.
The correct answer is b—The large number of nonpolar C–H bonds
B. Answer b is correct. Lipids are made up mostly of C–H bonds, which are nonpolar.
Hydrogen bonds can only form between two polar molecules. Water is polar, but lipids
are not.
The correct answer is b—
C. Answer c is incorrect. Saturated fatty acids are not branched.
The correct answer is b—
D. Answer d is incorrect. The ability to interact with water molecules (to be soluble) depends
on the presence of polar bonds within a molecule. The C=C bond is not polar.
15. The spontaneous formation of a lipid bilayer in an aqueous environment occurs because—
a. the polar head groups of the phospholipids can interact with water
b. the long fatty acid tails of the phospholipids can interact with water
c. the fatty acid tails of the phospholipids are hydrophobic
d. both a and c
The correct answer is d—
A. Answer a is incorrect. Since the head groups of the phospholipids are polar they are able
to interact with water; however, this is not the only property that contributes to the
formation of bilayers.
The correct answer is d—
B. Answer b is incorrect. The long-chain fatty acids are hydrophobic and as such do not
interact with polar water molecules.
Raven/Johnson Biology 8e
Chapter 03– Answers
The correct answer is d—
C. Answer c is incorrect. The hydrophobicity of the fatty acid tails will cause them to orient
themselves away from water; however, this is not the only property of a phospholipids
that contributes to the formation of a bilayer.
The correct answer is d—both a and c
D. Answer d is correct. Phospholipid molecules have both polar and nonpolar or hydrophilic
and hydrophobic properties. The chemical differences between the polar head groups and
the nonpolar fatty acid tails drive the formation of bilayers when these molecules are
exposed to an aqueous environment.
Challenge Questions
1. Spider webs are made of “silk,” which is a long, fibrous protein. The threads you see in a
web are actually composed of many individual proteins. One important structural motif
within spider’s silk protein is a “β crystal.” β crystals are regions where the β-pleated
sheets from the multiple individual protein fibers stack one upon the other. What chemical
bonds are required for the formation of the β crystals? What level of protein structure is
responsible for the formation of the silk you see in the web? Predict how the presence of
the β-crystal motif would influence the physical properties of the silk protein.
Answer—β-pleated sheets are regions of secondary protein structure that are held together by
hydrogen bonds. The hydrogen bonds are formed between regions of the amino acid backbone of
the protein (not between the R-groups). A β crystal would therefore be a region of β-pleated
sheets from many different silk proteins, all held together by hydrogen bonds. The formation of a
silk fiber is an example of quaternary protein structure because it involves many individual
proteins. The stacking and stabilization by hydrogen bonding of multiple β-pleated sheets would
create a stiff element within the protein. The β-crystal motif is associated with the strength of the
silk—the more regions of β crystal, the stronger the silk.
2. How do the four biological macromolecules differ from one another? Refer to the diagram
of the monomer structure in Figure 3.3 and summarize what “clues” you use to
distinguish between these important molecules.
Answer—Carbohydrates are characterized by the ratio of (CH2O)n. Carbohydrates will typically
form ring structures with lots of –OH and –H groups extending from the carbon ring.
Nucleic Acids are formed from nucleotides. A nucleotide is easy to recognize because it is made
up of three distinct chemical groups: a ribose (five-carbon) sugar, a phosphate group (PO4), and a
large nitrogenous base.
Proteins are composed of amino acids. An amino acid is easy to spot because of the distinct
carboxyl and amino groups at either end of the molecule. Also look for the variable R-groups that
extend from the central carbon.
Lipids might get confused with carbohydrates, but look closely and you will find that these
molecules have a lot less oxygen. Lots of carbons and hydrogens all lined up is the tip off that
you are looking at a lipid.
Raven/Johnson Biology 8e
Chapter 03– Answers
3. Hydrogen bonds play an important role in stabilizing and organizing biological
macromolecules. Consider the four macromolecules discussed in this chapter. Describe
three examples where hydrogen bond formation affects the form or function of the
macromolecule.
Answer—Nucleic Acids—Hydrogen bonds are important for complementary base-pairing
between the two strands of nucleic acid that make up a molecule of DNA. Complementary basepairing can also occur within the single nucleic acid strand of a RNA molecule.
Proteins—Hydrogen bonds are involved in both the secondary and tertiary levels of protein
structure. The α helices and β-pleated sheets of secondary structure are stabilized by hydrogen
bond formation between the amino and carboxyl groups of the amino acid backbone. Hydrogen
bond formation between R-groups helps stabilize the three-dimensional folding of the protein at
the tertiary level of structure.
Carbohydrates—Hydrogen bonds are less important for carbohydrates; however, these bonds are
responsible for the formation of the fibers of cellulose that make up the cell walls of plants.
Lipids—Hydrogen bonds are not involved in the structure of lipid molecules. The inability of
fatty acids to form hydrogen bonds with water is key to their hydrophobic nature.
4. The cells of your body are distinct even though they all contain the same genetic
information. A brain cell has a different shape and function than a muscle cell, and a skin
cell is very different from a blood cell. Use the information in Table 3.2 to develop an
explanation for the diversity of specialized cellular structure and function found within
your body.
Answer—The diversity of protein function underlies the diversity of cellular function. Table 3.2
is just a short list of examples of different protein functions. All cells possess the same genetic
“library,” however, different cells express different proteins. Muscle cells are specialized by their
expression of actin and myosin, two proteins associated with movement. Blood cells are
specialized to transport CO2 and O2 because of the presence of the protein hemoglobin in their
cytoplasm. The concepts of protein structure and function are critical to a good understanding of
biology because of this fundamental relationship between proteins and cells.