2025 BIO 1124 Exam 3 (Introductory Biology: Molecules,
Cells, and Physiology) New Latest Version with All 50
Multiple choice questions, Correct Answers and Rationales
Question 1
What is the primary source of energy for ATP production in eukaryotic cells?
A) Glucose
B) Oxygen
C) Carbon dioxide
D) Light
Correct Answer: A) Glucose
Rationale: Glucose is the primary substrate broken down during cellular respiration (glycolysis,
Krebs cycle, and oxidative phosphorylation) to produce ATP. Oxygen acts as an electron
acceptor, not an energy source, while carbon dioxide is a byproduct, and light is relevant only in
photosynthesis.
Question 2
Which organelle is responsible for protein synthesis in a eukaryotic cell?
A) Mitochondria
B) Ribosome
C) Golgi apparatus
D) Lysosome
Correct Answer: B) Ribosome
Rationale: Ribosomes, either free in the cytoplasm or bound to the endoplasmic reticulum,
synthesize proteins by translating mRNA. Mitochondria produce ATP, the Golgi modifies
proteins, and lysosomes degrade waste.
Question 3
During which phase of mitosis do sister chromatids separate?
A) Prophase
B) Metaphase
C) Anaphase
D) Telophase
Correct Answer: C) Anaphase
Rationale: In anaphase, the spindle fibers pull sister chromatids apart to opposite poles of the
cell. Prophase involves chromosome condensation, metaphase aligns chromosomes, and
telophase reforms nuclei.
Question 4
What molecule carries amino acids to the ribosome during translation?
A) mRNA
B) tRNA
C) rRNA
D) DNA
, Correct Answer: B) tRNA
Rationale: Transfer RNA (tRNA) brings specific amino acids to the ribosome, matching its
anticodon to the mRNA codon. mRNA provides the code, rRNA forms the ribosome, and DNA
remains in the nucleus.
Question 5
Which process directly requires oxygen in cellular respiration?
A) Glycolysis
B) Pyruvate oxidation
C) Krebs cycle
D) Electron transport chain
Correct Answer: D) Electron transport chain
Rationale: The electron transport chain uses oxygen as the final electron acceptor to form water,
driving ATP synthesis. Glycolysis, pyruvate oxidation, and the Krebs cycle do not directly
require oxygen (though they’re linked to aerobic respiration).
Question 6
What is the primary function of the sodium-potassium pump in cells?
A) Synthesize ATP
B) Maintain membrane potential
C) Transport glucose
D) Produce hormones
Correct Answer: B) Maintain membrane potential
Rationale: The sodium-potassium pump (Na+/K+ ATPase) uses ATP to move Na+ out and K+
into the cell, maintaining the electrochemical gradient across the membrane. It doesn’t synthesize
ATP, transport glucose, or produce hormones.
Question 7
Which type of molecule is the primary component of cell membranes?
A) Carbohydrates
B) Proteins
C) Phospholipids
D) Nucleic acids
Correct Answer: C) Phospholipids
Rationale: Phospholipids form the bilayer structure of cell membranes due to their hydrophilic
heads and hydrophobic tails. Proteins and carbohydrates play roles in membranes but aren’t the
primary structural component.
Question 8
What happens to enzyme activity if the pH deviates significantly from its optimal range?
A) It increases indefinitely
B) It decreases due to denaturation
C) It remains unchanged
D) It shifts to a new substrate
Correct Answer: B) It decreases due to denaturation
Rationale: Enzymes have an optimal pH; significant deviations disrupt their structure
Cells, and Physiology) New Latest Version with All 50
Multiple choice questions, Correct Answers and Rationales
Question 1
What is the primary source of energy for ATP production in eukaryotic cells?
A) Glucose
B) Oxygen
C) Carbon dioxide
D) Light
Correct Answer: A) Glucose
Rationale: Glucose is the primary substrate broken down during cellular respiration (glycolysis,
Krebs cycle, and oxidative phosphorylation) to produce ATP. Oxygen acts as an electron
acceptor, not an energy source, while carbon dioxide is a byproduct, and light is relevant only in
photosynthesis.
Question 2
Which organelle is responsible for protein synthesis in a eukaryotic cell?
A) Mitochondria
B) Ribosome
C) Golgi apparatus
D) Lysosome
Correct Answer: B) Ribosome
Rationale: Ribosomes, either free in the cytoplasm or bound to the endoplasmic reticulum,
synthesize proteins by translating mRNA. Mitochondria produce ATP, the Golgi modifies
proteins, and lysosomes degrade waste.
Question 3
During which phase of mitosis do sister chromatids separate?
A) Prophase
B) Metaphase
C) Anaphase
D) Telophase
Correct Answer: C) Anaphase
Rationale: In anaphase, the spindle fibers pull sister chromatids apart to opposite poles of the
cell. Prophase involves chromosome condensation, metaphase aligns chromosomes, and
telophase reforms nuclei.
Question 4
What molecule carries amino acids to the ribosome during translation?
A) mRNA
B) tRNA
C) rRNA
D) DNA
, Correct Answer: B) tRNA
Rationale: Transfer RNA (tRNA) brings specific amino acids to the ribosome, matching its
anticodon to the mRNA codon. mRNA provides the code, rRNA forms the ribosome, and DNA
remains in the nucleus.
Question 5
Which process directly requires oxygen in cellular respiration?
A) Glycolysis
B) Pyruvate oxidation
C) Krebs cycle
D) Electron transport chain
Correct Answer: D) Electron transport chain
Rationale: The electron transport chain uses oxygen as the final electron acceptor to form water,
driving ATP synthesis. Glycolysis, pyruvate oxidation, and the Krebs cycle do not directly
require oxygen (though they’re linked to aerobic respiration).
Question 6
What is the primary function of the sodium-potassium pump in cells?
A) Synthesize ATP
B) Maintain membrane potential
C) Transport glucose
D) Produce hormones
Correct Answer: B) Maintain membrane potential
Rationale: The sodium-potassium pump (Na+/K+ ATPase) uses ATP to move Na+ out and K+
into the cell, maintaining the electrochemical gradient across the membrane. It doesn’t synthesize
ATP, transport glucose, or produce hormones.
Question 7
Which type of molecule is the primary component of cell membranes?
A) Carbohydrates
B) Proteins
C) Phospholipids
D) Nucleic acids
Correct Answer: C) Phospholipids
Rationale: Phospholipids form the bilayer structure of cell membranes due to their hydrophilic
heads and hydrophobic tails. Proteins and carbohydrates play roles in membranes but aren’t the
primary structural component.
Question 8
What happens to enzyme activity if the pH deviates significantly from its optimal range?
A) It increases indefinitely
B) It decreases due to denaturation
C) It remains unchanged
D) It shifts to a new substrate
Correct Answer: B) It decreases due to denaturation
Rationale: Enzymes have an optimal pH; significant deviations disrupt their structure
