BIO 255 EXAM 2 COMPILATION QUESTIONS WITH VERIFIED ANSWERS PACKAGE DEAL
OBJECTIVE ASSESSMENT - EXAM
BIO 255 EXAM 2
COMPILATION QUESTIONS
WITH VERIFIED ANSWERS
PACKAGE DEAL
2026/2027 Official Exam
A+ Verified | Edition: 2026/2027 | Passing Score: 80%
COVER PAGE - 1
,SECTIONS COVERED
Section 1: Cell Biology & Membrane Transport
Section 2: Enzymes & Metabolism
Section 3: Cellular Respiration
Section 4: Photosynthesis
Section 5: Cell Signaling & Cell Cycle Regulation
SECTION 1: CELL BIOLOGY & MEMBRANE TRANSPORT
QUESTION 1
A marine biologist places a sample of red blood cells into a beaker of seawater and observes that the cells
shrink and become crenated. Which cellular process best explains this observation?
A. Facilitated diffusion of sodium ions into the cells
B. Osmotic water loss due to the hypertonic external environment
C. Active transport of chloride ions out of the cells
D. Endocytosis of extracellular solutes into the cytoplasm
Correct Answer: B
Rationale: Seawater is hypertonic relative to red blood cells, causing water to move out via osmosis. This water loss leads to
crenation. Option A describes ion movement, not the primary cause of shrinking.
QUESTION 2
A researcher discovers a mutant yeast strain that cannot grow on low-glucose media because glucose fails
to enter the cells rapidly enough. The glucose concentration inside these mutant cells remains far below
external levels even at 37°C. Which transport mechanism is most likely defective?
A. Simple diffusion through the lipid bilayer
B. Facilitated diffusion via carrier proteins
C. Active transport against a concentration gradient
D. Osmosis through aquaporin channels
Correct Answer: C
Rationale: When internal glucose remains far below external levels despite metabolic need, active transport is required to
accumulate it against the gradient. Simple and facilitated diffusion cannot concentrate solutes against gradients.
QUESTION 3
During an experiment on epithelial cell monolayers, a scientist applies a drug that binds to the external
surface of voltage-gated sodium channels and physically blocks the pore. Which type of transport is
directly inhibited?
A. Primary active transport using ATP hydrolysis
B. Passive transport of sodium down its electrochemical gradient
C. Secondary active transport of glucose via SGLT
D. Bulk-phase endocytosis of extracellular fluid
Correct Answer: B
Rationale: Voltage-gated sodium channels mediate passive transport of Na+ down its electrochemical gradient. Blocking the
channel pore directly inhibits this passive flow. Option C is indirectly affected but not directly inhibited.
, QUESTION 4
A student microinjects a small water-soluble fluorescent dye into one cell of a plant root tissue. After ten
minutes, the dye has spread to adjacent cells through narrow cytoplasmic channels but has not crossed
the plasma membrane into the cell wall space. Which structure explains this observation?
A. Tight junctions preventing paracellular diffusion
B. Plasmodesmata connecting neighboring plant cells
C. Gap junctions forming intercellular pores
D. Desmosomes anchoring cells together
Correct Answer: B
Rationale: Plasmodesmata are cytoplasmic channels in plant cell walls that allow direct communication between adjacent cells.
Gap junctions and tight junctions are animal structures, making B the only plant-appropriate answer.
QUESTION 5
In a classic experiment, isolated mitochondria are suspended in a buffered solution containing succinate.
As electrons flow through the respiratory chain, the external medium becomes measurably more acidic.
Which process occurring at the inner mitochondrial membrane directly causes this pH decrease?
A. Protons being pumped from the matrix into the intermembrane space
B. ATP synthase releasing protons into the matrix
C. Succinate dehydrogenase importing protons from the cytosol
D. Oxygen reduction consuming protons in the intermembrane space
Correct Answer: A
Rationale: Electron transport pumps protons from the matrix into the intermembrane space, acidifying the external medium
relative to the matrix. ATP synthase moves protons in the opposite direction, which would alkalinize the external medium.
QUESTION 6
A pharmaceutical chemist synthesizes a molecule that closely resembles the substrate of
acetylcholinesterase and competes with the natural substrate for the active site. When present, this
molecule slows but does not completely abolish enzyme activity at high substrate concentrations. What
type of inhibition is occurring?
A. Non-competitive inhibition
B. Uncompetitive inhibition
C. Competitive inhibition
D. Irreversible inhibition
Correct Answer: C
Rationale: A molecule resembling the substrate that competes for the active site and whose effects can be overcome by high
substrate concentrations defines competitive inhibition. Non-competitive inhibitors bind elsewhere and cannot be overcome by
excess substrate.
OBJECTIVE ASSESSMENT - EXAM
BIO 255 EXAM 2
COMPILATION QUESTIONS
WITH VERIFIED ANSWERS
PACKAGE DEAL
2026/2027 Official Exam
A+ Verified | Edition: 2026/2027 | Passing Score: 80%
COVER PAGE - 1
,SECTIONS COVERED
Section 1: Cell Biology & Membrane Transport
Section 2: Enzymes & Metabolism
Section 3: Cellular Respiration
Section 4: Photosynthesis
Section 5: Cell Signaling & Cell Cycle Regulation
SECTION 1: CELL BIOLOGY & MEMBRANE TRANSPORT
QUESTION 1
A marine biologist places a sample of red blood cells into a beaker of seawater and observes that the cells
shrink and become crenated. Which cellular process best explains this observation?
A. Facilitated diffusion of sodium ions into the cells
B. Osmotic water loss due to the hypertonic external environment
C. Active transport of chloride ions out of the cells
D. Endocytosis of extracellular solutes into the cytoplasm
Correct Answer: B
Rationale: Seawater is hypertonic relative to red blood cells, causing water to move out via osmosis. This water loss leads to
crenation. Option A describes ion movement, not the primary cause of shrinking.
QUESTION 2
A researcher discovers a mutant yeast strain that cannot grow on low-glucose media because glucose fails
to enter the cells rapidly enough. The glucose concentration inside these mutant cells remains far below
external levels even at 37°C. Which transport mechanism is most likely defective?
A. Simple diffusion through the lipid bilayer
B. Facilitated diffusion via carrier proteins
C. Active transport against a concentration gradient
D. Osmosis through aquaporin channels
Correct Answer: C
Rationale: When internal glucose remains far below external levels despite metabolic need, active transport is required to
accumulate it against the gradient. Simple and facilitated diffusion cannot concentrate solutes against gradients.
QUESTION 3
During an experiment on epithelial cell monolayers, a scientist applies a drug that binds to the external
surface of voltage-gated sodium channels and physically blocks the pore. Which type of transport is
directly inhibited?
A. Primary active transport using ATP hydrolysis
B. Passive transport of sodium down its electrochemical gradient
C. Secondary active transport of glucose via SGLT
D. Bulk-phase endocytosis of extracellular fluid
Correct Answer: B
Rationale: Voltage-gated sodium channels mediate passive transport of Na+ down its electrochemical gradient. Blocking the
channel pore directly inhibits this passive flow. Option C is indirectly affected but not directly inhibited.
, QUESTION 4
A student microinjects a small water-soluble fluorescent dye into one cell of a plant root tissue. After ten
minutes, the dye has spread to adjacent cells through narrow cytoplasmic channels but has not crossed
the plasma membrane into the cell wall space. Which structure explains this observation?
A. Tight junctions preventing paracellular diffusion
B. Plasmodesmata connecting neighboring plant cells
C. Gap junctions forming intercellular pores
D. Desmosomes anchoring cells together
Correct Answer: B
Rationale: Plasmodesmata are cytoplasmic channels in plant cell walls that allow direct communication between adjacent cells.
Gap junctions and tight junctions are animal structures, making B the only plant-appropriate answer.
QUESTION 5
In a classic experiment, isolated mitochondria are suspended in a buffered solution containing succinate.
As electrons flow through the respiratory chain, the external medium becomes measurably more acidic.
Which process occurring at the inner mitochondrial membrane directly causes this pH decrease?
A. Protons being pumped from the matrix into the intermembrane space
B. ATP synthase releasing protons into the matrix
C. Succinate dehydrogenase importing protons from the cytosol
D. Oxygen reduction consuming protons in the intermembrane space
Correct Answer: A
Rationale: Electron transport pumps protons from the matrix into the intermembrane space, acidifying the external medium
relative to the matrix. ATP synthase moves protons in the opposite direction, which would alkalinize the external medium.
QUESTION 6
A pharmaceutical chemist synthesizes a molecule that closely resembles the substrate of
acetylcholinesterase and competes with the natural substrate for the active site. When present, this
molecule slows but does not completely abolish enzyme activity at high substrate concentrations. What
type of inhibition is occurring?
A. Non-competitive inhibition
B. Uncompetitive inhibition
C. Competitive inhibition
D. Irreversible inhibition
Correct Answer: C
Rationale: A molecule resembling the substrate that competes for the active site and whose effects can be overcome by high
substrate concentrations defines competitive inhibition. Non-competitive inhibitors bind elsewhere and cannot be overcome by
excess substrate.
