HESI A2 Biology Test Bank 2025/2026
1. What is the primary source of energy for Earth’s ecosystems?
A. Geothermal heat
B. Sunlight
C. Wind
D. Fossil fuels
Answer: B
Rationale: Sunlight drives photosynthesis, producing energy-rich molecules that sus-
tain ecosystems. A, C, and D are secondary or non-biological energy sources.
2. Why is water considered a polar molecule?
A. It has an even charge distribution.
B. It has a partial positive and negative charge.
C. It lacks hydrogen bonds.
D. It is nonpolar covalent.
Answer: B
Rationale: Water’s oxygen atom attracts electrons more than hydrogen, creating
partial positive (hydrogen) and negative (oxygen) charges, making it polar. A, C, and
D are incorrect.
3. What is the role of enzymes in metabolism?
A. Store energy
B. Act as catalysts
C. Produce DNA
D. Form cell membranes
Answer: B
Rationale: Enzymes speed up metabolic reactions by lowering activation energy,
acting as catalysts. A, C, and D describe other functions.
4. Which molecule is the primary energy carrier in cells?
A. Glucose
B. ATP
C. DNA
D. RNA
Answer: B
Rationale: ATP (adenosine triphosphate) stores and transfers energy for cellular
processes. A is an energy source, and C and D carry genetic information.
5. What type of bond holds water molecules together in liquid form?
A. Covalent bond
B. Ionic bond
C. Hydrogen bond
D. Metallic bond
Answer: C
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, Rationale: Hydrogen bonds form between the partial positive hydrogen of one water
molecule and the partial negative oxygen of another, enabling cohesion. A, B, and D
are incorrect for water.
6. What is the basic unit of life?
A. Atom
B. Molecule
C. Cell
D. Tissue
Answer: C
Rationale: The cell is the smallest unit capable of performing life functions. A and
B are components, and D is a group of cells.
7. What organelle is responsible for protein synthesis?
A. Mitochondrion
B. Ribosome
C. Nucleus
D. Golgi apparatus
Answer: B
Rationale: Ribosomes assemble proteins by translating mRNA. A produces energy,
C stores DNA, and D modifies proteins.
8. What is the function of DNA in a cell?
A. Energy production
B. Storage of genetic information
C. Lipid synthesis
D. Cell movement
Answer: B
Rationale: DNA stores genetic instructions for building proteins and traits. A, C,
and D describe other cellular functions.
9. In genetics, what is a phenotype?
A. The genetic code
B. The observable traits of an organism
C. A recessive allele
D. A DNA mutation
Answer: B
Rationale: Phenotype is the physical or biochemical expression of an organism’s
genes. A is genotype, C is part of a genotype, and D causes changes in genes.
10. During which process is DNA replicated?
A. Translation
B. Transcription
C. Replication
D. Meiosis
Answer: C
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1. What is the primary source of energy for Earth’s ecosystems?
A. Geothermal heat
B. Sunlight
C. Wind
D. Fossil fuels
Answer: B
Rationale: Sunlight drives photosynthesis, producing energy-rich molecules that sus-
tain ecosystems. A, C, and D are secondary or non-biological energy sources.
2. Why is water considered a polar molecule?
A. It has an even charge distribution.
B. It has a partial positive and negative charge.
C. It lacks hydrogen bonds.
D. It is nonpolar covalent.
Answer: B
Rationale: Water’s oxygen atom attracts electrons more than hydrogen, creating
partial positive (hydrogen) and negative (oxygen) charges, making it polar. A, C, and
D are incorrect.
3. What is the role of enzymes in metabolism?
A. Store energy
B. Act as catalysts
C. Produce DNA
D. Form cell membranes
Answer: B
Rationale: Enzymes speed up metabolic reactions by lowering activation energy,
acting as catalysts. A, C, and D describe other functions.
4. Which molecule is the primary energy carrier in cells?
A. Glucose
B. ATP
C. DNA
D. RNA
Answer: B
Rationale: ATP (adenosine triphosphate) stores and transfers energy for cellular
processes. A is an energy source, and C and D carry genetic information.
5. What type of bond holds water molecules together in liquid form?
A. Covalent bond
B. Ionic bond
C. Hydrogen bond
D. Metallic bond
Answer: C
1
, Rationale: Hydrogen bonds form between the partial positive hydrogen of one water
molecule and the partial negative oxygen of another, enabling cohesion. A, B, and D
are incorrect for water.
6. What is the basic unit of life?
A. Atom
B. Molecule
C. Cell
D. Tissue
Answer: C
Rationale: The cell is the smallest unit capable of performing life functions. A and
B are components, and D is a group of cells.
7. What organelle is responsible for protein synthesis?
A. Mitochondrion
B. Ribosome
C. Nucleus
D. Golgi apparatus
Answer: B
Rationale: Ribosomes assemble proteins by translating mRNA. A produces energy,
C stores DNA, and D modifies proteins.
8. What is the function of DNA in a cell?
A. Energy production
B. Storage of genetic information
C. Lipid synthesis
D. Cell movement
Answer: B
Rationale: DNA stores genetic instructions for building proteins and traits. A, C,
and D describe other cellular functions.
9. In genetics, what is a phenotype?
A. The genetic code
B. The observable traits of an organism
C. A recessive allele
D. A DNA mutation
Answer: B
Rationale: Phenotype is the physical or biochemical expression of an organism’s
genes. A is genotype, C is part of a genotype, and D causes changes in genes.
10. During which process is DNA replicated?
A. Translation
B. Transcription
C. Replication
D. Meiosis
Answer: C
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