HESI A2 Biology Exam – 2025 Edition
– Actual Questions & 100% Correct
Answers | Pass Guaranteed
1. Which of the following structures is primarily responsible for protein synthesis in
eukaryotic cells?
o A. Nucleus
o B. Ribosome
o C. Mitochondrion
o D. Golgi apparatus Rationale: Ribosomes are the cellular organelles where
translation occurs, assembling amino acids into polypeptide chains based on
mRNA instructions, a fundamental principle of the central dogma of molecular
biology.
2. In DNA replication, which enzyme is responsible for unwinding the double helix?
o A. DNA polymerase
o B. Helicase
o C. Ligase
o D. Primase Rationale: Helicase breaks hydrogen bonds between complementary
base pairs, separating the strands to allow semi-conservative replication, ensuring
genetic fidelity during cell division.
3. Which type of bond links amino acids together in a protein chain?
o A. Ionic bond
o B. Peptide bond
o C. Hydrogen bond
o D. Covalent bond (non-peptide) Rationale: Peptide bonds form through
dehydration synthesis between the carboxyl group of one amino acid and the
amino group of another, creating the primary structure of proteins essential for
enzymatic function.
4. During mitosis, which phase involves the shortening and thickening of chromosomes?
o A. Prophase
o B. Prophase
o C. Metaphase
o D. Anaphase Rationale: In prophase, chromatin condenses into visible
chromosomes via histone modifications, preparing for equitable distribution of
genetic material to daughter cells.
5. What is the primary function of the Golgi apparatus in eukaryotic cells?
o A. Energy production
o B. Modification and packaging of proteins
o C. DNA storage
o D. Waste removal Rationale: The Golgi apparatus processes and sorts
proteins/lipids from the ER, adding modifications like glycosylation for proper
cellular targeting and secretion.
, 6. Which of the following is a characteristic of prokaryotic cells?
o A. Membrane-bound nucleus
o B. Lack of membrane-bound organelles
o C. Linear chromosomes
o D. 80S ribosomes Rationale: Prokaryotes, like bacteria, have a nucleoid region
instead of a nucleus and simpler ribosomes (70S), enabling rapid reproduction in
diverse environments.
7. In cellular respiration, where does the Krebs cycle occur?
o A. Cytoplasm
o B. Mitochondrial matrix
o C. Inner mitochondrial membrane
o D. Intermembrane space Rationale: The Krebs cycle oxidizes acetyl-CoA in the
matrix, generating electron carriers (NADH/FADH2) for ATP production via
oxidative phosphorylation.
8. Which molecule serves as the primary energy currency in cells?
o A. Glucose
o B. ATP
o C. NADH
o D. FADH2 Rationale: ATP hydrolysis releases energy (ΔG ≈ -7.3 kcal/mol) for
endergonic reactions, maintaining cellular homeostasis through coupled reactions.
9. What is the role of tRNA in translation?
o A. Carries the genetic code
o B. Transfers amino acids to the ribosome
o C. Synthesizes mRNA
o D. Proofreads DNA Rationale: tRNA's anticodon pairs with mRNA codons,
delivering specific amino acids for polypeptide elongation per the genetic code's
universality.
10. Which process involves the fusion of male and female gametes?
o A. Mitosis
o B. Fertilization
o C. Meiosis
o D. Binary fission Rationale: Fertilization restores diploidy (2n) by combining
haploid gametes, initiating embryonic development and genetic diversity via
independent assortment.
11. In Mendelian genetics, which term describes the physical expression of a gene?
o A. Genotype
o B. Phenotype
o C. Allele
o D. Homozygous Rationale: Phenotype results from genotype-environment
interactions, as seen in Punnett squares predicting trait ratios like 3:1 in
monohybrid crosses.
12. What is the function of the sodium-potassium pump in neurons?
o A. Action potential propagation
o B. Maintaining resting membrane potential
o C. Synaptic transmission
– Actual Questions & 100% Correct
Answers | Pass Guaranteed
1. Which of the following structures is primarily responsible for protein synthesis in
eukaryotic cells?
o A. Nucleus
o B. Ribosome
o C. Mitochondrion
o D. Golgi apparatus Rationale: Ribosomes are the cellular organelles where
translation occurs, assembling amino acids into polypeptide chains based on
mRNA instructions, a fundamental principle of the central dogma of molecular
biology.
2. In DNA replication, which enzyme is responsible for unwinding the double helix?
o A. DNA polymerase
o B. Helicase
o C. Ligase
o D. Primase Rationale: Helicase breaks hydrogen bonds between complementary
base pairs, separating the strands to allow semi-conservative replication, ensuring
genetic fidelity during cell division.
3. Which type of bond links amino acids together in a protein chain?
o A. Ionic bond
o B. Peptide bond
o C. Hydrogen bond
o D. Covalent bond (non-peptide) Rationale: Peptide bonds form through
dehydration synthesis between the carboxyl group of one amino acid and the
amino group of another, creating the primary structure of proteins essential for
enzymatic function.
4. During mitosis, which phase involves the shortening and thickening of chromosomes?
o A. Prophase
o B. Prophase
o C. Metaphase
o D. Anaphase Rationale: In prophase, chromatin condenses into visible
chromosomes via histone modifications, preparing for equitable distribution of
genetic material to daughter cells.
5. What is the primary function of the Golgi apparatus in eukaryotic cells?
o A. Energy production
o B. Modification and packaging of proteins
o C. DNA storage
o D. Waste removal Rationale: The Golgi apparatus processes and sorts
proteins/lipids from the ER, adding modifications like glycosylation for proper
cellular targeting and secretion.
, 6. Which of the following is a characteristic of prokaryotic cells?
o A. Membrane-bound nucleus
o B. Lack of membrane-bound organelles
o C. Linear chromosomes
o D. 80S ribosomes Rationale: Prokaryotes, like bacteria, have a nucleoid region
instead of a nucleus and simpler ribosomes (70S), enabling rapid reproduction in
diverse environments.
7. In cellular respiration, where does the Krebs cycle occur?
o A. Cytoplasm
o B. Mitochondrial matrix
o C. Inner mitochondrial membrane
o D. Intermembrane space Rationale: The Krebs cycle oxidizes acetyl-CoA in the
matrix, generating electron carriers (NADH/FADH2) for ATP production via
oxidative phosphorylation.
8. Which molecule serves as the primary energy currency in cells?
o A. Glucose
o B. ATP
o C. NADH
o D. FADH2 Rationale: ATP hydrolysis releases energy (ΔG ≈ -7.3 kcal/mol) for
endergonic reactions, maintaining cellular homeostasis through coupled reactions.
9. What is the role of tRNA in translation?
o A. Carries the genetic code
o B. Transfers amino acids to the ribosome
o C. Synthesizes mRNA
o D. Proofreads DNA Rationale: tRNA's anticodon pairs with mRNA codons,
delivering specific amino acids for polypeptide elongation per the genetic code's
universality.
10. Which process involves the fusion of male and female gametes?
o A. Mitosis
o B. Fertilization
o C. Meiosis
o D. Binary fission Rationale: Fertilization restores diploidy (2n) by combining
haploid gametes, initiating embryonic development and genetic diversity via
independent assortment.
11. In Mendelian genetics, which term describes the physical expression of a gene?
o A. Genotype
o B. Phenotype
o C. Allele
o D. Homozygous Rationale: Phenotype results from genotype-environment
interactions, as seen in Punnett squares predicting trait ratios like 3:1 in
monohybrid crosses.
12. What is the function of the sodium-potassium pump in neurons?
o A. Action potential propagation
o B. Maintaining resting membrane potential
o C. Synaptic transmission
