BIOL 355 Midterm Exam | Foundations in Molecular Cell
Biology | 2026/2027 Complete Practice Questions, Correct
Answers & Detailed Rationales
PART I — CELL BIOLOGY FOUNDATIONS
1.
Which feature best distinguishes eukaryotic cells from prokaryotic cells?
A. Presence of DNA
B. Presence of ribosomes
C. Presence of membrane-bound organelles
D. Presence of a plasma membrane
Correct Answer: C. Presence of membrane-bound organelles
Rationale: Eukaryotic cells contain membrane-bound compartments
such as the nucleus, ER, and Golgi. Both cell types contain DNA,
ribosomes, and plasma membranes.
2.
Which organelle contains most of the genetic material in a typical
eukaryotic cell?
A. Golgi apparatus
B. Nucleus
C. Lysosome
D. Peroxisome
,Correct Answer: B. Nucleus
Rationale: Nuclear chromosomes contain most eukaryotic genomic
DNA. Mitochondria also contain small genomes.
3.
What is the primary function of ribosomes?
A. Lipid storage
B. Protein synthesis
C. DNA replication
D. ATP storage
Correct Answer: B. Protein synthesis
Rationale: Ribosomes translate mRNA into polypeptide chains.
4.
Which organelle is most directly associated with ATP production
through oxidative phosphorylation?
A. Lysosome
B. Golgi apparatus
C. Mitochondrion
D. Nucleolus
Correct Answer: C. Mitochondrion
Rationale: The mitochondrial inner membrane contains the electron
transport chain and ATP synthase.
5.
The nucleolus is primarily involved in:
,A. Lipid synthesis
B. Ribosome subunit production
C. Protein degradation
D. Membrane trafficking
Correct Answer: B. Ribosome subunit production
Rationale: The nucleolus synthesizes rRNA and assembles ribosomal
subunits.
6.
Which organelle is the major site of protein folding for proteins entering
the secretory pathway?
A. Rough ER
B. Lysosome
C. Peroxisome
D. Centrosome
Correct Answer: A. Rough ER
Rationale: Secretory and many membrane proteins enter the ER during
synthesis, where folding and quality control occur.
7.
Which organelle modifies, sorts, and distributes many proteins received
from the ER?
A. Nucleus
B. Golgi apparatus
C. Mitochondrion
D. Peroxisome
, Correct Answer: B. Golgi apparatus
Rationale: Golgi cisternae process proteins and sort them toward
different destinations.
8.
Lysosomes are specialized primarily for:
A. Protein synthesis
B. Intracellular digestion
C. DNA transcription
D. ATP synthesis
Correct Answer: B. Intracellular digestion
Rationale: Lysosomes contain hydrolytic enzymes that degrade
macromolecules.
9.
Peroxisomes are particularly important for:
A. Oxidative reactions and lipid metabolism
B. Translation
C. Ribosome assembly
D. Chromosome segregation
Correct Answer: A. Oxidative reactions and lipid metabolism
Rationale: Peroxisomes contain oxidative enzymes and participate in
fatty-acid metabolism and hydrogen peroxide handling.
10.
Which statement about organelles is most accurate?
Biology | 2026/2027 Complete Practice Questions, Correct
Answers & Detailed Rationales
PART I — CELL BIOLOGY FOUNDATIONS
1.
Which feature best distinguishes eukaryotic cells from prokaryotic cells?
A. Presence of DNA
B. Presence of ribosomes
C. Presence of membrane-bound organelles
D. Presence of a plasma membrane
Correct Answer: C. Presence of membrane-bound organelles
Rationale: Eukaryotic cells contain membrane-bound compartments
such as the nucleus, ER, and Golgi. Both cell types contain DNA,
ribosomes, and plasma membranes.
2.
Which organelle contains most of the genetic material in a typical
eukaryotic cell?
A. Golgi apparatus
B. Nucleus
C. Lysosome
D. Peroxisome
,Correct Answer: B. Nucleus
Rationale: Nuclear chromosomes contain most eukaryotic genomic
DNA. Mitochondria also contain small genomes.
3.
What is the primary function of ribosomes?
A. Lipid storage
B. Protein synthesis
C. DNA replication
D. ATP storage
Correct Answer: B. Protein synthesis
Rationale: Ribosomes translate mRNA into polypeptide chains.
4.
Which organelle is most directly associated with ATP production
through oxidative phosphorylation?
A. Lysosome
B. Golgi apparatus
C. Mitochondrion
D. Nucleolus
Correct Answer: C. Mitochondrion
Rationale: The mitochondrial inner membrane contains the electron
transport chain and ATP synthase.
5.
The nucleolus is primarily involved in:
,A. Lipid synthesis
B. Ribosome subunit production
C. Protein degradation
D. Membrane trafficking
Correct Answer: B. Ribosome subunit production
Rationale: The nucleolus synthesizes rRNA and assembles ribosomal
subunits.
6.
Which organelle is the major site of protein folding for proteins entering
the secretory pathway?
A. Rough ER
B. Lysosome
C. Peroxisome
D. Centrosome
Correct Answer: A. Rough ER
Rationale: Secretory and many membrane proteins enter the ER during
synthesis, where folding and quality control occur.
7.
Which organelle modifies, sorts, and distributes many proteins received
from the ER?
A. Nucleus
B. Golgi apparatus
C. Mitochondrion
D. Peroxisome
, Correct Answer: B. Golgi apparatus
Rationale: Golgi cisternae process proteins and sort them toward
different destinations.
8.
Lysosomes are specialized primarily for:
A. Protein synthesis
B. Intracellular digestion
C. DNA transcription
D. ATP synthesis
Correct Answer: B. Intracellular digestion
Rationale: Lysosomes contain hydrolytic enzymes that degrade
macromolecules.
9.
Peroxisomes are particularly important for:
A. Oxidative reactions and lipid metabolism
B. Translation
C. Ribosome assembly
D. Chromosome segregation
Correct Answer: A. Oxidative reactions and lipid metabolism
Rationale: Peroxisomes contain oxidative enzymes and participate in
fatty-acid metabolism and hydrogen peroxide handling.
10.
Which statement about organelles is most accurate?
