Table of Contents
1. Unit 1: The Scientific Method, Chemistry of Life, and Macromolecules
(Questions 1–25)
2. Unit 2: Cell Structure, Membranes, and Transport (Questions 26–50)
3. Unit 3: Metabolism, Cellular Respiration, and Photosynthesis (Questions
51–75)
4. Unit 4: The Cell Cycle, Genetics, and Molecular Biology (Questions 76–105)
5. Unit 5: Evolution, Biological Diversity, and Classification (Questions 106–
130)
6. Unit 6: Plant and Animal Form & Function, and Ecology (Questions 131–
150)
7. Answer Key with Rationales
Unit 1: The Scientific Method, Chemistry of Life, and
Macromolecules
🟢 1. A researcher hypothesizes that a new fertilizer increases tomato plant yield. She
treats 50 plants with the fertilizer and 50 with water. At the end of the season, the
fertilized plants produced, on average, 20% more tomatoes. However, she later realizes
that the fertilized group was also placed in a greenhouse that received 2 extra hours of
sunlight per day. In this scenario, the extra sunlight is best described as a(n):
A) Dependent variable
B) Controlled variable
,🔴🔴 C) Confounding variable
D) Null hypothesis
Rationale: A confounding variable is an unintended variable that varies along with the
independent variable and can influence the dependent variable. The extra sunlight could
be the actual cause of the increased yield, not the fertilizer.
🟢 2. Which property of water is most directly responsible for its ability to moderate
temperature on Earth?
A) Its high polarity
B) Its cohesive and adhesive properties
🔴🔴 C) Its high specific heat and high heat of vaporization
D) Its lower density as a solid compared to its liquid state
Rationale: Water’s high specific heat allows it to absorb large amounts of heat with
little change in its own temperature, and its high heat of vaporization allows evaporative
cooling. These properties buffer ecosystems against temperature extremes.
🟢 3. A mutation changes a single amino acid in an enzyme's active site from a polar
serine to a nonpolar valine. This substitution is most likely to disrupt which level(s) of
protein structure directly?
A) Primary structure only
B) Secondary structure only
🔴🔴 C) Tertiary structure, and potentially quaternary structure
D) Primary and secondary structures, but not tertiary structure
Rationale: The primary structure is altered by the amino acid substitution. This change
can disrupt the hydrogen bonds and ionic interactions that stabilize the tertiary
structure, especially in the active site, which may also affect quaternary structure if the
protein is multi-subunit.
🟢 4. A student is investigating the effect of pH on amylase activity. They predict that the
enzyme will function best at pH 7. Which of the following would be the most
appropriate control for this experiment?
A) A test tube with amylase and starch at pH 7
B) A test tube with starch and no amylase at pH 7
🔴🔴 C) A test tube with amylase and starch at pH 3
D) A test tube with amylase and no starch at pH 7
,Rationale: A control for the independent variable (pH) would be to test the enzyme at
a different pH to compare activity. A negative control (no enzyme) is also useful, but to
test the hypothesis about the optimal pH, comparing to another pH is a direct control.
🟢 5. The spontaneous formation of a lipid bilayer in water is primarily driven by:
A) Covalent bonds between fatty acid tails
🔴🔴 B) The hydrophobic effect
C) Hydrogen bonds between the phosphate heads
D) The high solubility of the hydrophobic tails
Rationale: The hydrophobic effect is the tendency of nonpolar molecules (like lipid
tails) to aggregate in an aqueous environment, minimizing their disruptive effect on the
hydrogen-bonded network of water. This is the primary driving force for membrane self-
assembly.
🟢 6. Which of the following statements about the carbon atom is false?
A) It can form four covalent bonds.
B) It can form double and triple bonds.
🔴🔴 C) It is the most electronegative atom in organic molecules.
D) It can bond with atoms of many different elements.
Rationale: Carbon is not highly electronegative; it is more electronegative than
hydrogen but less than oxygen and nitrogen. Its versatility comes from its tetravalency
and ability to catenate, not high electronegativity.
🟢 7. A particular polypeptide has the sequence Met-Ala-Trp-Arg-Glu. Which amino acid
in this sequence is most likely to be found in the hydrophobic core of a folded globular
protein?
A) Arginine (Arg)
B) Glutamic acid (Glu)
🔴🔴 C) Tryptophan (Trp)
D) Methionine (Met) and Alanine (Ala) are equally likely
Rationale: Tryptophan has a large, nonpolar aromatic side chain, making it highly
hydrophobic. Arginine and glutamic acid are charged (hydrophilic). Methionine and
alanine are also hydrophobic, but tryptophan’s large nonpolar surface area makes it a
strong candidate for the protein core.
🟢 8. The “Miller-Urey experiment” was designed to test the hypothesis that:
A) Life originated on another planet.
🔴🔴 B) Simple organic molecules could form from inorganic precursors under conditions
, simulating the early Earth.
C) DNA is the genetic material.
D) Cells can arise spontaneously from nonliving matter.
Rationale: The Miller-Urey experiment simulated a primitive atmosphere and used
electrical sparks to mimic lightning, producing amino acids and other organic molecules,
supporting the abiotic synthesis hypothesis for the origin of life.
🟢 9. A buffer system in a cell consists of carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻).
If a small amount of strong acid (H⁺) is added to the cell, which component of the buffer
system will neutralize it?
A) H₂CO₃
🔴🔴 B) HCO₃⁻
C) Both will neutralize the acid equally.
D) Neither; a strong acid cannot be buffered.
Rationale: Bicarbonate (HCO₃⁻) is the conjugate base in this buffer system. It can
accept H⁺ ions to form carbonic acid, thereby minimizing the change in pH.
🟢 10. Which of the following is a key difference between starch and cellulose?
A) Starch is a polymer of glucose, while cellulose is a polymer of fructose.
B) Starch is found in animals, while cellulose is found in plants.
🔴🔴 C) The glycosidic linkages in cellulose are β-1,4, while in starch they are α-1,4.
D) Cellulose is highly branched, while starch is unbranched.
Rationale: The difference in the glycosidic linkage (alpha vs. beta) is crucial. Humans
have enzymes (amylases) that can break alpha linkages in starch but lack the enzyme
(cellulase) to break beta linkages in cellulose.
🟢 11. A researcher discovers a new organism. It is unicellular, lacks a nucleus, and has a
cell wall. Which of the following is the most reasonable conclusion?
A) It is a eukaryotic cell.
🔴🔴 B) It is a prokaryotic cell.
C) It is a virus.
D) It is a fungal cell.
Rationale: The lack of a nucleus and the presence of a cell wall are characteristic of
prokaryotes (bacteria and archaea). Viruses are not cells and do not have a cell wall in
the same sense.
🟢 12. Which of the following best describes the role of ATP in cells?
A) It is a long-term energy storage molecule.
1. Unit 1: The Scientific Method, Chemistry of Life, and Macromolecules
(Questions 1–25)
2. Unit 2: Cell Structure, Membranes, and Transport (Questions 26–50)
3. Unit 3: Metabolism, Cellular Respiration, and Photosynthesis (Questions
51–75)
4. Unit 4: The Cell Cycle, Genetics, and Molecular Biology (Questions 76–105)
5. Unit 5: Evolution, Biological Diversity, and Classification (Questions 106–
130)
6. Unit 6: Plant and Animal Form & Function, and Ecology (Questions 131–
150)
7. Answer Key with Rationales
Unit 1: The Scientific Method, Chemistry of Life, and
Macromolecules
🟢 1. A researcher hypothesizes that a new fertilizer increases tomato plant yield. She
treats 50 plants with the fertilizer and 50 with water. At the end of the season, the
fertilized plants produced, on average, 20% more tomatoes. However, she later realizes
that the fertilized group was also placed in a greenhouse that received 2 extra hours of
sunlight per day. In this scenario, the extra sunlight is best described as a(n):
A) Dependent variable
B) Controlled variable
,🔴🔴 C) Confounding variable
D) Null hypothesis
Rationale: A confounding variable is an unintended variable that varies along with the
independent variable and can influence the dependent variable. The extra sunlight could
be the actual cause of the increased yield, not the fertilizer.
🟢 2. Which property of water is most directly responsible for its ability to moderate
temperature on Earth?
A) Its high polarity
B) Its cohesive and adhesive properties
🔴🔴 C) Its high specific heat and high heat of vaporization
D) Its lower density as a solid compared to its liquid state
Rationale: Water’s high specific heat allows it to absorb large amounts of heat with
little change in its own temperature, and its high heat of vaporization allows evaporative
cooling. These properties buffer ecosystems against temperature extremes.
🟢 3. A mutation changes a single amino acid in an enzyme's active site from a polar
serine to a nonpolar valine. This substitution is most likely to disrupt which level(s) of
protein structure directly?
A) Primary structure only
B) Secondary structure only
🔴🔴 C) Tertiary structure, and potentially quaternary structure
D) Primary and secondary structures, but not tertiary structure
Rationale: The primary structure is altered by the amino acid substitution. This change
can disrupt the hydrogen bonds and ionic interactions that stabilize the tertiary
structure, especially in the active site, which may also affect quaternary structure if the
protein is multi-subunit.
🟢 4. A student is investigating the effect of pH on amylase activity. They predict that the
enzyme will function best at pH 7. Which of the following would be the most
appropriate control for this experiment?
A) A test tube with amylase and starch at pH 7
B) A test tube with starch and no amylase at pH 7
🔴🔴 C) A test tube with amylase and starch at pH 3
D) A test tube with amylase and no starch at pH 7
,Rationale: A control for the independent variable (pH) would be to test the enzyme at
a different pH to compare activity. A negative control (no enzyme) is also useful, but to
test the hypothesis about the optimal pH, comparing to another pH is a direct control.
🟢 5. The spontaneous formation of a lipid bilayer in water is primarily driven by:
A) Covalent bonds between fatty acid tails
🔴🔴 B) The hydrophobic effect
C) Hydrogen bonds between the phosphate heads
D) The high solubility of the hydrophobic tails
Rationale: The hydrophobic effect is the tendency of nonpolar molecules (like lipid
tails) to aggregate in an aqueous environment, minimizing their disruptive effect on the
hydrogen-bonded network of water. This is the primary driving force for membrane self-
assembly.
🟢 6. Which of the following statements about the carbon atom is false?
A) It can form four covalent bonds.
B) It can form double and triple bonds.
🔴🔴 C) It is the most electronegative atom in organic molecules.
D) It can bond with atoms of many different elements.
Rationale: Carbon is not highly electronegative; it is more electronegative than
hydrogen but less than oxygen and nitrogen. Its versatility comes from its tetravalency
and ability to catenate, not high electronegativity.
🟢 7. A particular polypeptide has the sequence Met-Ala-Trp-Arg-Glu. Which amino acid
in this sequence is most likely to be found in the hydrophobic core of a folded globular
protein?
A) Arginine (Arg)
B) Glutamic acid (Glu)
🔴🔴 C) Tryptophan (Trp)
D) Methionine (Met) and Alanine (Ala) are equally likely
Rationale: Tryptophan has a large, nonpolar aromatic side chain, making it highly
hydrophobic. Arginine and glutamic acid are charged (hydrophilic). Methionine and
alanine are also hydrophobic, but tryptophan’s large nonpolar surface area makes it a
strong candidate for the protein core.
🟢 8. The “Miller-Urey experiment” was designed to test the hypothesis that:
A) Life originated on another planet.
🔴🔴 B) Simple organic molecules could form from inorganic precursors under conditions
, simulating the early Earth.
C) DNA is the genetic material.
D) Cells can arise spontaneously from nonliving matter.
Rationale: The Miller-Urey experiment simulated a primitive atmosphere and used
electrical sparks to mimic lightning, producing amino acids and other organic molecules,
supporting the abiotic synthesis hypothesis for the origin of life.
🟢 9. A buffer system in a cell consists of carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻).
If a small amount of strong acid (H⁺) is added to the cell, which component of the buffer
system will neutralize it?
A) H₂CO₃
🔴🔴 B) HCO₃⁻
C) Both will neutralize the acid equally.
D) Neither; a strong acid cannot be buffered.
Rationale: Bicarbonate (HCO₃⁻) is the conjugate base in this buffer system. It can
accept H⁺ ions to form carbonic acid, thereby minimizing the change in pH.
🟢 10. Which of the following is a key difference between starch and cellulose?
A) Starch is a polymer of glucose, while cellulose is a polymer of fructose.
B) Starch is found in animals, while cellulose is found in plants.
🔴🔴 C) The glycosidic linkages in cellulose are β-1,4, while in starch they are α-1,4.
D) Cellulose is highly branched, while starch is unbranched.
Rationale: The difference in the glycosidic linkage (alpha vs. beta) is crucial. Humans
have enzymes (amylases) that can break alpha linkages in starch but lack the enzyme
(cellulase) to break beta linkages in cellulose.
🟢 11. A researcher discovers a new organism. It is unicellular, lacks a nucleus, and has a
cell wall. Which of the following is the most reasonable conclusion?
A) It is a eukaryotic cell.
🔴🔴 B) It is a prokaryotic cell.
C) It is a virus.
D) It is a fungal cell.
Rationale: The lack of a nucleus and the presence of a cell wall are characteristic of
prokaryotes (bacteria and archaea). Viruses are not cells and do not have a cell wall in
the same sense.
🟢 12. Which of the following best describes the role of ATP in cells?
A) It is a long-term energy storage molecule.
