University of Michigan
1 MAXE · 171 OIB
★ ★
M College of Literature, Science & the Arts — Department of Biology
EST. 1817
ARTES · SCIENTIA · VERITAS
BIO 171 EXAM 1
C E L L B I O LO G Y · B I O C H E M I ST RY · M O L E CU L A R G E N E T I CS · E VO LU T I O N
INSTITUTION University of Michigan PROGRAM Bachelor of Science — Biology
COURSE CODE BIO 171 COURSE TITLE Introduction to Molecular &
Cellular Biology
ACADEMIC YEAR EXAM TITLE BIO 171 EXAM 1
TOTAL QUESTIONS 47 Questions FORMAT Multiple Choice — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ This examination covers cell biology, biochemistry, molecular genetics, evolutionary biology, and
related foundational concepts.
▸ Questions address homeostasis, protein structure, chemical bonding, cellular organization, and the
properties of biological macromolecules.
▸ Correct answers and explanatory rationales appear below each question for review purposes.
▸ All content reflects standard introductory molecular and cellular biology curriculum.
, SECTION I — MOLECULAR & CELLULAR BIOLOGY Questions 1 – 47
1. A sodium atom has lost an electron, and a chlorine atom has gained an electron forming
NaCl. Which of the following is correct?
A. Sodium is now a cation
B. Chlorine is now an anion
C. NaCl is held together by an ionic bond
D. All of these
CORRECT ANSWER D — All of these
RATIONALE When sodium (Na) loses an electron, it becomes a positively charged cation (Na+).
When chlorine (Cl) gains an electron, it becomes a negatively charged anion (Cl-).
The electrostatic attraction between the oppositely charged ions forms an ionic
bond, creating the compound NaCl. Therefore, all three statements are correct.
This is a fundamental example of ionic bonding in biology and chemistry.
2. You have an unknown molecule. When you place it in water, it forms a bilayer vesicle.
Which property would you predict that best describes the molecule?
A. Hydrophilic
B. Hydrophobic
C. Amphipathic
D. Lipophilic
CORRECT ANSWER C — Amphipathic
RATIONALE Bilayer vesicles form spontaneously when amphipathic molecules — those
possessing both hydrophilic (water-loving) and hydrophobic (water-fearing)
regions — are placed in water. The hydrophobic regions orient inward away from
water while the hydrophilic regions face the aqueous environment. Phospholipids
are the classic example, forming the foundation of all biological membranes.
Purely hydrophilic molecules dissolve, and purely hydrophobic molecules
aggregate separately rather than forming organized bilayers.
, 3. Carbon and hydrogen have similar electronegativities and combine to form hydrocarbon
molecules. What type of chemical properties do we expect from these molecules?
A. Hydrophilic
B. Hydrophobic
C. Amphipathic
D. Acidic
CORRECT ANSWER B — Hydrophobic
RATIONALE When atoms with similar electronegativity bond, electrons are shared relatively
equally, producing nonpolar covalent bonds. Carbon-hydrogen bonds are
nonpolar, making hydrocarbons hydrophobic (water-repelling). These molecules
do not interact favorably with polar water molecules and tend to cluster together
in aqueous environments. This property is fundamental to the behavior of lipids
and the formation of cellular membranes.
4. What chemical characteristics allow a phospholipid to form a bilayer membrane?
A. It's hydrophilic
B. It's hydrophobic
C. It's amphipathic
D. It's lipophilic
CORRECT ANSWER C — It's amphipathic
RATIONALE Phospholipids are amphipathic — they possess a hydrophilic (polar) phosphate
"head" and two hydrophobic (nonpolar) fatty acid "tails." In aqueous
environments, this dual nature drives the spontaneous formation of bilayers:
hydrophobic tails face inward (shielded from water), while hydrophilic heads face
outward toward the aqueous environment on both sides. This self-assembly is the
molecular basis of all cellular membranes.
1 MAXE · 171 OIB
★ ★
M College of Literature, Science & the Arts — Department of Biology
EST. 1817
ARTES · SCIENTIA · VERITAS
BIO 171 EXAM 1
C E L L B I O LO G Y · B I O C H E M I ST RY · M O L E CU L A R G E N E T I CS · E VO LU T I O N
INSTITUTION University of Michigan PROGRAM Bachelor of Science — Biology
COURSE CODE BIO 171 COURSE TITLE Introduction to Molecular &
Cellular Biology
ACADEMIC YEAR EXAM TITLE BIO 171 EXAM 1
TOTAL QUESTIONS 47 Questions FORMAT Multiple Choice — Select the
Single Best Answer
EXAMINATION INSTRUCTIONS
▸ Select the single best answer for each question unless otherwise instructed.
▸ This examination covers cell biology, biochemistry, molecular genetics, evolutionary biology, and
related foundational concepts.
▸ Questions address homeostasis, protein structure, chemical bonding, cellular organization, and the
properties of biological macromolecules.
▸ Correct answers and explanatory rationales appear below each question for review purposes.
▸ All content reflects standard introductory molecular and cellular biology curriculum.
, SECTION I — MOLECULAR & CELLULAR BIOLOGY Questions 1 – 47
1. A sodium atom has lost an electron, and a chlorine atom has gained an electron forming
NaCl. Which of the following is correct?
A. Sodium is now a cation
B. Chlorine is now an anion
C. NaCl is held together by an ionic bond
D. All of these
CORRECT ANSWER D — All of these
RATIONALE When sodium (Na) loses an electron, it becomes a positively charged cation (Na+).
When chlorine (Cl) gains an electron, it becomes a negatively charged anion (Cl-).
The electrostatic attraction between the oppositely charged ions forms an ionic
bond, creating the compound NaCl. Therefore, all three statements are correct.
This is a fundamental example of ionic bonding in biology and chemistry.
2. You have an unknown molecule. When you place it in water, it forms a bilayer vesicle.
Which property would you predict that best describes the molecule?
A. Hydrophilic
B. Hydrophobic
C. Amphipathic
D. Lipophilic
CORRECT ANSWER C — Amphipathic
RATIONALE Bilayer vesicles form spontaneously when amphipathic molecules — those
possessing both hydrophilic (water-loving) and hydrophobic (water-fearing)
regions — are placed in water. The hydrophobic regions orient inward away from
water while the hydrophilic regions face the aqueous environment. Phospholipids
are the classic example, forming the foundation of all biological membranes.
Purely hydrophilic molecules dissolve, and purely hydrophobic molecules
aggregate separately rather than forming organized bilayers.
, 3. Carbon and hydrogen have similar electronegativities and combine to form hydrocarbon
molecules. What type of chemical properties do we expect from these molecules?
A. Hydrophilic
B. Hydrophobic
C. Amphipathic
D. Acidic
CORRECT ANSWER B — Hydrophobic
RATIONALE When atoms with similar electronegativity bond, electrons are shared relatively
equally, producing nonpolar covalent bonds. Carbon-hydrogen bonds are
nonpolar, making hydrocarbons hydrophobic (water-repelling). These molecules
do not interact favorably with polar water molecules and tend to cluster together
in aqueous environments. This property is fundamental to the behavior of lipids
and the formation of cellular membranes.
4. What chemical characteristics allow a phospholipid to form a bilayer membrane?
A. It's hydrophilic
B. It's hydrophobic
C. It's amphipathic
D. It's lipophilic
CORRECT ANSWER C — It's amphipathic
RATIONALE Phospholipids are amphipathic — they possess a hydrophilic (polar) phosphate
"head" and two hydrophobic (nonpolar) fatty acid "tails." In aqueous
environments, this dual nature drives the spontaneous formation of bilayers:
hydrophobic tails face inward (shielded from water), while hydrophilic heads face
outward toward the aqueous environment on both sides. This self-assembly is the
molecular basis of all cellular membranes.
