CHEM 210 Module 5 - Original Practice Assessment Page 1
,CHEM 210 Module 5 Exam | Biochemistry |
Portage | Q & A | 26/27 Actual (PDF)
Original Practice Assessment
100 multiple-choice practice questions with full-text answers and rationales
Scope: lipid definition and classes; fatty-acid structure and nomenclature; triacylglycerols; glycerophospholipids;
sphingolipids; sterols; membrane organization, fluidity, proteins, and transport.
1. A compound dissolves readily in hexane but only sparingly in water. Which molecular feature best
explains its classification as a lipid?
A) A large nonpolar hydrocarbon region
B) Several freely ionized phosphate groups
C) A high density of peptide bonds
D) A repeating charged polysaccharide backbone
Correct Answer: A large nonpolar hydrocarbon region
Rationale: A substantial nonpolar region favors solubility in nonpolar solvents, matching the
functional definition used for lipids in this module. Ionized phosphates, peptide-rich backbones, and
charged polysaccharides increase polarity and interaction with water rather than nonpolar solvents.
This distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
2. Consider two molecules of similar molar mass: one is a hydrocarbon-rich lipid and the other
contains many hydroxyl groups. In water, the lipid is expected to
A) form extensive hydrogen bonds with water
B) show lower solubility because hydrophobic surface dominates
C) ionize completely at neutral pH
D) behave as a strong electrolyte
Correct Answer: show lower solubility because hydrophobic surface dominates
CHEM 210 Module 5 - Original Practice Assessment Page 2
, Rationale: Hydrocarbon-rich surfaces interact poorly with water, so the lipid has lower aqueous
solubility despite a molar mass similar to the hydroxyl-rich compound. Hydroxyl groups promote
hydrogen bonding, whereas complete ionization and strong-electrolyte behavior require suitable
ionizable groups rather than simple hydrocarbon content. This distinction follows from the module’s
structure-property relationships for lipids and membranes.
3. A researcher adds a purified lipid to a biphasic mixture of water and a nonpolar solvent. Most of
the material enters the nonpolar phase. This observation most directly supports which conclusion?
A) The molecule must contain nitrogen
B) The molecule is necessarily a sterol
C) The molecule has substantial hydrophobic character
D) The molecule must contain three fatty acids
Correct Answer: The molecule has substantial hydrophobic character
Rationale: Preferential partitioning into a nonpolar solvent demonstrates substantial hydrophobic
character, a central functional property of lipids. Nitrogen content, sterol identity, and a three-fatty-
acid structure are possible for some lipids but cannot be inferred from solvent partitioning alone.
This distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
4. A synthetic molecule has a polar head group attached to two long hydrocarbon chains. When
dispersed in water at sufficient concentration, the most likely organization is
A) a covalent polymer network
B) a crystal of isolated polar heads
C) a solution of fully separated molecules
D) a self-assembled structure with hydrocarbon regions shielded from water
Correct Answer: a self-assembled structure with hydrocarbon regions shielded from water
Rationale: An amphipathic molecule minimizes unfavorable hydrocarbon-water contacts by self-
assembling so that hydrophobic regions are buried while polar heads remain exposed. Covalent
polymerization is unnecessary, isolated head-group crystals ignore the hydrophobic effect, and fully
separated molecules would expose too much nonpolar surface to water. This distinction follows
from the module’s structure-property relationships for lipids and membranes.
5. A classmate states that every lipid is completely nonpolar. Which correction is most accurate?
A) Many lipids are amphipathic, containing both polar and nonpolar regions
B) All lipids are ionic at physiological pH
C) Only sterols qualify as lipids
D) Lipids are defined by possessing glycerol
CHEM 210 Module 5 - Original Practice Assessment Page 3
, Correct Answer: Many lipids are amphipathic, containing both polar and nonpolar regions
Rationale: Many biologically important lipids are amphipathic, combining hydrophobic hydrocarbon
regions with polar or charged head groups. Universal ionization, sterol-only classification, and a
glycerol requirement are incorrect because lipid classes vary widely in structure and polarity. This
distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
6. A membrane lipid is extracted more efficiently by chloroform than by water. Which interaction
contributes most to this behavior?
A) Strong attraction between charged head groups and bulk water
B) Favorable dispersion interactions between hydrocarbon regions and the nonpolar solvent
C) Covalent bond formation with chloroform
D) Irreversible ionization of the lipid
Correct Answer: Favorable dispersion interactions between hydrocarbon regions and the nonpolar
solvent
Rationale: Nonpolar solvents stabilize hydrocarbon surfaces through favorable dispersion
interactions, improving extraction of lipids with large hydrophobic regions. Strong hydration would
favor the aqueous phase, while covalent reaction and irreversible ionization are not required for
routine solvent partitioning. This distinction follows directly from the structural and physical
principles used to classify lipids and explain membrane organization in this module.
7. A molecule contains a long hydrocarbon chain ending in a carboxyl group. Within the Module 5
classification, it belongs most directly to the class of
A) sterols
B) sphingolipids
C) fatty acids
D) triacylglycerols
Correct Answer: fatty acids
Rationale: A long aliphatic chain terminating in a carboxyl group is the defining structural pattern of
a fatty acid. Sterols have fused rings, sphingolipids use a sphingosine-like backbone, and
triacylglycerols contain glycerol esterified to three fatty acids. This distinction follows directly from
the structural and physical principles used to classify lipids and explain membrane organization in
this module.
8. An unknown lipid has four fused hydrocarbon rings and a small hydroxyl group. The strongest
classification
is
A) fatty acid
CHEM 210 Module 5 - Original Practice Assessment Page 4
,CHEM 210 Module 5 Exam | Biochemistry |
Portage | Q & A | 26/27 Actual (PDF)
Original Practice Assessment
100 multiple-choice practice questions with full-text answers and rationales
Scope: lipid definition and classes; fatty-acid structure and nomenclature; triacylglycerols; glycerophospholipids;
sphingolipids; sterols; membrane organization, fluidity, proteins, and transport.
1. A compound dissolves readily in hexane but only sparingly in water. Which molecular feature best
explains its classification as a lipid?
A) A large nonpolar hydrocarbon region
B) Several freely ionized phosphate groups
C) A high density of peptide bonds
D) A repeating charged polysaccharide backbone
Correct Answer: A large nonpolar hydrocarbon region
Rationale: A substantial nonpolar region favors solubility in nonpolar solvents, matching the
functional definition used for lipids in this module. Ionized phosphates, peptide-rich backbones, and
charged polysaccharides increase polarity and interaction with water rather than nonpolar solvents.
This distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
2. Consider two molecules of similar molar mass: one is a hydrocarbon-rich lipid and the other
contains many hydroxyl groups. In water, the lipid is expected to
A) form extensive hydrogen bonds with water
B) show lower solubility because hydrophobic surface dominates
C) ionize completely at neutral pH
D) behave as a strong electrolyte
Correct Answer: show lower solubility because hydrophobic surface dominates
CHEM 210 Module 5 - Original Practice Assessment Page 2
, Rationale: Hydrocarbon-rich surfaces interact poorly with water, so the lipid has lower aqueous
solubility despite a molar mass similar to the hydroxyl-rich compound. Hydroxyl groups promote
hydrogen bonding, whereas complete ionization and strong-electrolyte behavior require suitable
ionizable groups rather than simple hydrocarbon content. This distinction follows from the module’s
structure-property relationships for lipids and membranes.
3. A researcher adds a purified lipid to a biphasic mixture of water and a nonpolar solvent. Most of
the material enters the nonpolar phase. This observation most directly supports which conclusion?
A) The molecule must contain nitrogen
B) The molecule is necessarily a sterol
C) The molecule has substantial hydrophobic character
D) The molecule must contain three fatty acids
Correct Answer: The molecule has substantial hydrophobic character
Rationale: Preferential partitioning into a nonpolar solvent demonstrates substantial hydrophobic
character, a central functional property of lipids. Nitrogen content, sterol identity, and a three-fatty-
acid structure are possible for some lipids but cannot be inferred from solvent partitioning alone.
This distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
4. A synthetic molecule has a polar head group attached to two long hydrocarbon chains. When
dispersed in water at sufficient concentration, the most likely organization is
A) a covalent polymer network
B) a crystal of isolated polar heads
C) a solution of fully separated molecules
D) a self-assembled structure with hydrocarbon regions shielded from water
Correct Answer: a self-assembled structure with hydrocarbon regions shielded from water
Rationale: An amphipathic molecule minimizes unfavorable hydrocarbon-water contacts by self-
assembling so that hydrophobic regions are buried while polar heads remain exposed. Covalent
polymerization is unnecessary, isolated head-group crystals ignore the hydrophobic effect, and fully
separated molecules would expose too much nonpolar surface to water. This distinction follows
from the module’s structure-property relationships for lipids and membranes.
5. A classmate states that every lipid is completely nonpolar. Which correction is most accurate?
A) Many lipids are amphipathic, containing both polar and nonpolar regions
B) All lipids are ionic at physiological pH
C) Only sterols qualify as lipids
D) Lipids are defined by possessing glycerol
CHEM 210 Module 5 - Original Practice Assessment Page 3
, Correct Answer: Many lipids are amphipathic, containing both polar and nonpolar regions
Rationale: Many biologically important lipids are amphipathic, combining hydrophobic hydrocarbon
regions with polar or charged head groups. Universal ionization, sterol-only classification, and a
glycerol requirement are incorrect because lipid classes vary widely in structure and polarity. This
distinction follows directly from the structural and physical principles used to classify lipids and
explain membrane organization in this module.
6. A membrane lipid is extracted more efficiently by chloroform than by water. Which interaction
contributes most to this behavior?
A) Strong attraction between charged head groups and bulk water
B) Favorable dispersion interactions between hydrocarbon regions and the nonpolar solvent
C) Covalent bond formation with chloroform
D) Irreversible ionization of the lipid
Correct Answer: Favorable dispersion interactions between hydrocarbon regions and the nonpolar
solvent
Rationale: Nonpolar solvents stabilize hydrocarbon surfaces through favorable dispersion
interactions, improving extraction of lipids with large hydrophobic regions. Strong hydration would
favor the aqueous phase, while covalent reaction and irreversible ionization are not required for
routine solvent partitioning. This distinction follows directly from the structural and physical
principles used to classify lipids and explain membrane organization in this module.
7. A molecule contains a long hydrocarbon chain ending in a carboxyl group. Within the Module 5
classification, it belongs most directly to the class of
A) sterols
B) sphingolipids
C) fatty acids
D) triacylglycerols
Correct Answer: fatty acids
Rationale: A long aliphatic chain terminating in a carboxyl group is the defining structural pattern of
a fatty acid. Sterols have fused rings, sphingolipids use a sphingosine-like backbone, and
triacylglycerols contain glycerol esterified to three fatty acids. This distinction follows directly from
the structural and physical principles used to classify lipids and explain membrane organization in
this module.
8. An unknown lipid has four fused hydrocarbon rings and a small hydroxyl group. The strongest
classification
is
A) fatty acid
CHEM 210 Module 5 - Original Practice Assessment Page 4
