HESI Biology [2026/2027] Updated
Version | Verified Questions &
Detailed Rationales for Top
Performance
Course Hesi
1. A student examines a cell under a microscope and observes a distinct nucleus and
membrane-bound organelles. Which type of cell is being observed?
A. Prokaryotic cell
B. Eukaryotic cell
C. Virus
D. Prion
Correct Answer: B. Eukaryotic cell
Rationale: Eukaryotic cells contain a membrane-bound nucleus and organelles such as
mitochondria and the endoplasmic reticulum. Prokaryotes, including bacteria, lack a membrane-
bound nucleus. Viruses and prions are not cells.
2. A cell requires large amounts of energy to perform its functions. Which organelle is
primarily responsible for producing ATP through aerobic cellular respiration?
A. Lysosome
B. Golgi apparatus
C. Mitochondrion
D. Ribosome
Correct Answer: C. Mitochondrion
Rationale: Mitochondria produce most ATP during aerobic cellular respiration through the citric
acid cycle and oxidative phosphorylation. Ribosomes synthesize proteins, lysosomes digest
cellular materials, and the Golgi apparatus modifies and packages proteins and lipids.
3. A red blood cell is placed in a hypotonic solution. What is most likely to happen?
A. Water leaves the cell, causing it to shrink
B. Water enters the cell, causing it to swell
C. No water movement occurs
D. The cell immediately produces a cell wall
Correct Answer: B. Water enters the cell, causing it to swell
,Rationale: A hypotonic solution has a lower solute concentration than the cell's interior. Water
moves into the cell by osmosis, potentially causing the red blood cell to swell and burst. In a
hypertonic solution, water would move out of the cell.
4. Which process produces two genetically similar daughter cells for growth and tissue
repair?
A. Meiosis
B. Fertilization
C. Mitosis
D. Crossing over
Correct Answer: C. Mitosis
Rationale: Mitosis distributes duplicated chromosomes into two daughter nuclei, usually
producing two genetically similar daughter cells with the same chromosome number as the
parent cell. Meiosis produces haploid cells and contributes to genetic variation.
5. A DNA molecule contains 30% adenine. Assuming it is double-stranded DNA, what
percentage of the bases are cytosine?
A. 20%
B. 30%
C. 40%
D. 70%
Correct Answer: A. 20%
Rationale: In double-stranded DNA, adenine pairs with thymine, and cytosine pairs with
guanine. If adenine is 30%, thymine is also 30%. The remaining 40% is divided equally between
cytosine and guanine, so cytosine is 20%.
6. During protein synthesis, which molecule carries genetic instructions copied from DNA
to the ribosome?
A. Messenger RNA (mRNA)
B. Transfer RNA (tRNA)
C. Glycogen
D. Phospholipid
Correct Answer: A. Messenger RNA (mRNA)
Rationale: Messenger RNA carries a transcribed copy of genetic information from DNA to the
ribosome. Transfer RNA brings amino acids to the ribosome, where the amino acids are
assembled into a protein according to the mRNA sequence.
, 7. A heterozygous individual has the genotype Aa for a trait in which A is completely
dominant over a. What phenotype is expected?
A. The recessive phenotype only
B. The dominant phenotype
C. Both phenotypes must appear equally
D. No phenotype will develop
Correct Answer: B. The dominant phenotype
Rationale: With complete dominance, one copy of the dominant allele is sufficient for the
dominant phenotype to be expressed. Therefore, an individual with genotype Aa displays the
dominant phenotype, although the recessive allele can be passed to offspring.
8. Two heterozygous parents (Aa × Aa) have a child. What is the probability that the child
will have the homozygous recessive genotype aa?
A. 0%
B. 25%
C. 50%
D. 75%
Correct Answer: B. 25%
Rationale: Each parent can contribute either A or a. The possible offspring genotypes are AA, Aa,
Aa, and aa. One of the four combinations is aa, giving a probability of 1/4, or 25%, for each
pregnancy.
9. Which statement best describes the function of enzymes in living organisms?
A. They increase activation energy
B. They are consumed permanently in every reaction
C. They lower activation energy and speed up reactions
D. They change the final equilibrium of every reaction
Correct Answer: C. They lower activation energy and speed up reactions
Rationale: Enzymes are biological catalysts that accelerate chemical reactions by lowering
activation energy. They are not permanently consumed by the reactions they catalyze, and they
do not change the overall equilibrium of a reversible reaction.
10. A plant is placed in sunlight and uses carbon dioxide and water to produce glucose.
Which process is occurring?
A. Cellular respiration
B. Photosynthesis
Version | Verified Questions &
Detailed Rationales for Top
Performance
Course Hesi
1. A student examines a cell under a microscope and observes a distinct nucleus and
membrane-bound organelles. Which type of cell is being observed?
A. Prokaryotic cell
B. Eukaryotic cell
C. Virus
D. Prion
Correct Answer: B. Eukaryotic cell
Rationale: Eukaryotic cells contain a membrane-bound nucleus and organelles such as
mitochondria and the endoplasmic reticulum. Prokaryotes, including bacteria, lack a membrane-
bound nucleus. Viruses and prions are not cells.
2. A cell requires large amounts of energy to perform its functions. Which organelle is
primarily responsible for producing ATP through aerobic cellular respiration?
A. Lysosome
B. Golgi apparatus
C. Mitochondrion
D. Ribosome
Correct Answer: C. Mitochondrion
Rationale: Mitochondria produce most ATP during aerobic cellular respiration through the citric
acid cycle and oxidative phosphorylation. Ribosomes synthesize proteins, lysosomes digest
cellular materials, and the Golgi apparatus modifies and packages proteins and lipids.
3. A red blood cell is placed in a hypotonic solution. What is most likely to happen?
A. Water leaves the cell, causing it to shrink
B. Water enters the cell, causing it to swell
C. No water movement occurs
D. The cell immediately produces a cell wall
Correct Answer: B. Water enters the cell, causing it to swell
,Rationale: A hypotonic solution has a lower solute concentration than the cell's interior. Water
moves into the cell by osmosis, potentially causing the red blood cell to swell and burst. In a
hypertonic solution, water would move out of the cell.
4. Which process produces two genetically similar daughter cells for growth and tissue
repair?
A. Meiosis
B. Fertilization
C. Mitosis
D. Crossing over
Correct Answer: C. Mitosis
Rationale: Mitosis distributes duplicated chromosomes into two daughter nuclei, usually
producing two genetically similar daughter cells with the same chromosome number as the
parent cell. Meiosis produces haploid cells and contributes to genetic variation.
5. A DNA molecule contains 30% adenine. Assuming it is double-stranded DNA, what
percentage of the bases are cytosine?
A. 20%
B. 30%
C. 40%
D. 70%
Correct Answer: A. 20%
Rationale: In double-stranded DNA, adenine pairs with thymine, and cytosine pairs with
guanine. If adenine is 30%, thymine is also 30%. The remaining 40% is divided equally between
cytosine and guanine, so cytosine is 20%.
6. During protein synthesis, which molecule carries genetic instructions copied from DNA
to the ribosome?
A. Messenger RNA (mRNA)
B. Transfer RNA (tRNA)
C. Glycogen
D. Phospholipid
Correct Answer: A. Messenger RNA (mRNA)
Rationale: Messenger RNA carries a transcribed copy of genetic information from DNA to the
ribosome. Transfer RNA brings amino acids to the ribosome, where the amino acids are
assembled into a protein according to the mRNA sequence.
, 7. A heterozygous individual has the genotype Aa for a trait in which A is completely
dominant over a. What phenotype is expected?
A. The recessive phenotype only
B. The dominant phenotype
C. Both phenotypes must appear equally
D. No phenotype will develop
Correct Answer: B. The dominant phenotype
Rationale: With complete dominance, one copy of the dominant allele is sufficient for the
dominant phenotype to be expressed. Therefore, an individual with genotype Aa displays the
dominant phenotype, although the recessive allele can be passed to offspring.
8. Two heterozygous parents (Aa × Aa) have a child. What is the probability that the child
will have the homozygous recessive genotype aa?
A. 0%
B. 25%
C. 50%
D. 75%
Correct Answer: B. 25%
Rationale: Each parent can contribute either A or a. The possible offspring genotypes are AA, Aa,
Aa, and aa. One of the four combinations is aa, giving a probability of 1/4, or 25%, for each
pregnancy.
9. Which statement best describes the function of enzymes in living organisms?
A. They increase activation energy
B. They are consumed permanently in every reaction
C. They lower activation energy and speed up reactions
D. They change the final equilibrium of every reaction
Correct Answer: C. They lower activation energy and speed up reactions
Rationale: Enzymes are biological catalysts that accelerate chemical reactions by lowering
activation energy. They are not permanently consumed by the reactions they catalyze, and they
do not change the overall equilibrium of a reversible reaction.
10. A plant is placed in sunlight and uses carbon dioxide and water to produce glucose.
Which process is occurring?
A. Cellular respiration
B. Photosynthesis
