HESI A2 Biology Exam 2025/2026 –
Verified Questions, Correct Answers, and
Expert Rationales
Question 1
What is the primary function of the mitochondria in a eukaryotic cell?
A. Synthesize proteins
B. Produce ATP
C. Store genetic material
D. Package secretions
Rationale: Mitochondria are the powerhouses of the cell, producing ATP through cellular
respiration via the electron transport chain and oxidative phosphorylation. Protein synthesis
occurs in ribosomes, genetic material is stored in the nucleus, and the Golgi apparatus packages
secretions.
Question 2
Which molecule is the primary component of the cell membrane?
A. Carbohydrate
B. Protein
C. Phospholipid
D. Nucleic acid
Rationale: Phospholipids form the bilayer structure of cell membranes, with hydrophilic heads
facing outward and hydrophobic tails inward. Proteins facilitate transport, carbohydrates aid in
cell recognition, and nucleic acids store genetic information.
Question 3
During which phase of the cell cycle does DNA replication occur?
A. G2 phase
B. S phase
C. M phase
D. G1 phase
,Rationale: DNA replication occurs during the S (synthesis) phase of the cell cycle, ensuring
each daughter cell receives an identical copy of the genome. G1 and G2 are growth phases, and
M phase involves mitosis and cytokinesis.
Question 4
What is the term for a change in the DNA sequence?
A. Transcription
B. Translation
C. Mutation
D. Replication
Rationale: A mutation is an alteration in the DNA sequence, which can affect gene function.
Transcription produces RNA, translation synthesizes proteins, and replication copies DNA.
Question 5
Which process describes the movement of water across a semipermeable membrane?
A. Diffusion
B. Osmosis
C. Active transport
D. Facilitated diffusion
Rationale: Osmosis is the passive movement of water across a semipermeable membrane from a
region of lower solute concentration to higher solute concentration. Diffusion moves solutes,
active transport requires energy, and facilitated diffusion uses carriers.
Question 6
Which organelle is responsible for modifying and packaging proteins for secretion?
A. Lysosome
B. Mitochondrion
C. Golgi apparatus
D. Endoplasmic reticulum
Rationale: The Golgi apparatus modifies, sorts, and packages proteins for secretion or use
within the cell. Lysosomes degrade waste, mitochondria produce ATP, and the endoplasmic
reticulum synthesizes proteins and lipids.
, Question 7
What is the primary source of genetic variation in sexually reproducing organisms?
A. Mitosis
B. Crossing over
C. DNA replication
D. Transcription
Rationale: Crossing over during meiosis I exchanges genetic material between homologous
chromosomes, creating genetic diversity. Mitosis produces identical cells, DNA replication
copies DNA, and transcription produces RNA.
Question 8
Which type of RNA carries the genetic code from the nucleus to the ribosome?
A. tRNA
B. mRNA
C. rRNA
D. snRNA
Rationale: Messenger RNA (mRNA) carries the genetic code from DNA in the nucleus to the
ribosome for protein synthesis. tRNA delivers amino acids, rRNA forms ribosomes, and snRNA
aids in RNA splicing.
Question 9
What is the primary function of the large intestine in the human digestive system?
A. Digest proteins
B. Absorb water and form feces
C. Produce bile
D. Absorb nutrients
Rationale: The large intestine absorbs water and electrolytes, forming feces from undigested
material. Protein digestion occurs in the stomach and small intestine, bile is produced by the
liver, and nutrient absorption occurs primarily in the small intestine.
Question 10
Which phase of mitosis involves the separation of sister chromatids?
Verified Questions, Correct Answers, and
Expert Rationales
Question 1
What is the primary function of the mitochondria in a eukaryotic cell?
A. Synthesize proteins
B. Produce ATP
C. Store genetic material
D. Package secretions
Rationale: Mitochondria are the powerhouses of the cell, producing ATP through cellular
respiration via the electron transport chain and oxidative phosphorylation. Protein synthesis
occurs in ribosomes, genetic material is stored in the nucleus, and the Golgi apparatus packages
secretions.
Question 2
Which molecule is the primary component of the cell membrane?
A. Carbohydrate
B. Protein
C. Phospholipid
D. Nucleic acid
Rationale: Phospholipids form the bilayer structure of cell membranes, with hydrophilic heads
facing outward and hydrophobic tails inward. Proteins facilitate transport, carbohydrates aid in
cell recognition, and nucleic acids store genetic information.
Question 3
During which phase of the cell cycle does DNA replication occur?
A. G2 phase
B. S phase
C. M phase
D. G1 phase
,Rationale: DNA replication occurs during the S (synthesis) phase of the cell cycle, ensuring
each daughter cell receives an identical copy of the genome. G1 and G2 are growth phases, and
M phase involves mitosis and cytokinesis.
Question 4
What is the term for a change in the DNA sequence?
A. Transcription
B. Translation
C. Mutation
D. Replication
Rationale: A mutation is an alteration in the DNA sequence, which can affect gene function.
Transcription produces RNA, translation synthesizes proteins, and replication copies DNA.
Question 5
Which process describes the movement of water across a semipermeable membrane?
A. Diffusion
B. Osmosis
C. Active transport
D. Facilitated diffusion
Rationale: Osmosis is the passive movement of water across a semipermeable membrane from a
region of lower solute concentration to higher solute concentration. Diffusion moves solutes,
active transport requires energy, and facilitated diffusion uses carriers.
Question 6
Which organelle is responsible for modifying and packaging proteins for secretion?
A. Lysosome
B. Mitochondrion
C. Golgi apparatus
D. Endoplasmic reticulum
Rationale: The Golgi apparatus modifies, sorts, and packages proteins for secretion or use
within the cell. Lysosomes degrade waste, mitochondria produce ATP, and the endoplasmic
reticulum synthesizes proteins and lipids.
, Question 7
What is the primary source of genetic variation in sexually reproducing organisms?
A. Mitosis
B. Crossing over
C. DNA replication
D. Transcription
Rationale: Crossing over during meiosis I exchanges genetic material between homologous
chromosomes, creating genetic diversity. Mitosis produces identical cells, DNA replication
copies DNA, and transcription produces RNA.
Question 8
Which type of RNA carries the genetic code from the nucleus to the ribosome?
A. tRNA
B. mRNA
C. rRNA
D. snRNA
Rationale: Messenger RNA (mRNA) carries the genetic code from DNA in the nucleus to the
ribosome for protein synthesis. tRNA delivers amino acids, rRNA forms ribosomes, and snRNA
aids in RNA splicing.
Question 9
What is the primary function of the large intestine in the human digestive system?
A. Digest proteins
B. Absorb water and form feces
C. Produce bile
D. Absorb nutrients
Rationale: The large intestine absorbs water and electrolytes, forming feces from undigested
material. Protein digestion occurs in the stomach and small intestine, bile is produced by the
liver, and nutrient absorption occurs primarily in the small intestine.
Question 10
Which phase of mitosis involves the separation of sister chromatids?
