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BIOLOGY FOR AP® COURSES Original
Comprehensive Study Guide & Exam Questions
with Answers and Rationales
Unit 1: Chemistry of Life (Chapters 1–3) (Questions)
1. Which of the following elements is the most abundant in
living organisms?
A. Nitrogen
B. Carbon
C. Oxygen
D. Hydrogen
Answer: C
Rationale: Oxygen is the most abundant element in living
organisms by mass (approximately 65%), primarily
because it is a component of water (H₂O), which makes
up the majority of body mass. Carbon is the backbone of
organic molecules but is second to oxygen in total mass.
2. What type of bond is formed when two atoms share
electrons equally?
A. Ionic bond
B. Polar covalent bond
C. Nonpolar covalent bond
D. Hydrogen bond
Answer: C
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Rationale: A nonpolar covalent bond forms when
electrons are shared equally between atoms with similar
electronegativities (e.g., C-H bonds). Polar covalent bonds
share unequally; ionic bonds transfer electrons; hydrogen
bonds are weak attractions between molecules.
3. What property of water allows it to act as a universal
solvent?
A. High specific heat
B. Polarity
C. Cohesion
D. Adhesion
Answer: B
Rationale: Water's polarity—the partial positive charge
on hydrogen and partial negative charge on oxygen—
allows it to dissolve polar and ionic substances by
surrounding charged particles and separating them.
4. What is the pH of a neutral solution at 25°C?
A. 0
B. 5
C. 7
D. 14
Answer: C
Rationale: A neutral solution has a pH of 7, where the
concentration of hydrogen ions [H⁺] equals the
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concentration of hydroxide ions [OH⁻]. pH <7 is acidic; pH
>7 is basic.
5. Which macromolecule is the primary source of quick
energy for cells?
A. Protein
B. Lipid
C. Carbohydrate
D. Nucleic acid
Answer: C
Rationale: Carbohydrates (glucose, glycogen, starch) are
the primary source of quick energy. They are broken
down rapidly through cellular respiration to produce ATP.
6. What is the monomer of proteins?
A. Nucleotide
B. Monosaccharide
C. Amino acid
D. Fatty acid
Answer: C
Rationale: Proteins are polymers of amino acids linked by
peptide bonds. Nucleotides form nucleic acids;
monosaccharides form carbohydrates; fatty acids form
lipids.
7. What is the function of enzymes in biological systems?
A. To provide energy
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B. To act as biological catalysts, lowering activation energy
C. To store genetic information
D. To form cell membranes
Answer: B
Rationale: Enzymes are proteins that catalyze biochemical
reactions by lowering the activation energy required,
speeding up reactions without being consumed.
8. What is "denaturation" of a protein?
A. The synthesis of a protein
B. The loss of a protein's three-dimensional structure and
function due to heat, pH, or chemicals
C. The folding of a protein
D. The transport of a protein
Answer: B
Rationale: Denaturation disrupts the secondary, tertiary,
and quaternary structures of a protein, causing loss of
function. It can be caused by high temperature, extreme
pH, or chemicals. Primary structure (amino acid
sequence) remains intact.
9. Which organic molecule is the primary component of cell
membranes?
A. Carbohydrate
B. Phospholipid
C. Nucleic acid
BIOLOGY FOR AP® COURSES Original
Comprehensive Study Guide & Exam Questions
with Answers and Rationales
Unit 1: Chemistry of Life (Chapters 1–3) (Questions)
1. Which of the following elements is the most abundant in
living organisms?
A. Nitrogen
B. Carbon
C. Oxygen
D. Hydrogen
Answer: C
Rationale: Oxygen is the most abundant element in living
organisms by mass (approximately 65%), primarily
because it is a component of water (H₂O), which makes
up the majority of body mass. Carbon is the backbone of
organic molecules but is second to oxygen in total mass.
2. What type of bond is formed when two atoms share
electrons equally?
A. Ionic bond
B. Polar covalent bond
C. Nonpolar covalent bond
D. Hydrogen bond
Answer: C
,https://www.stuvia.com/user/performance
Rationale: A nonpolar covalent bond forms when
electrons are shared equally between atoms with similar
electronegativities (e.g., C-H bonds). Polar covalent bonds
share unequally; ionic bonds transfer electrons; hydrogen
bonds are weak attractions between molecules.
3. What property of water allows it to act as a universal
solvent?
A. High specific heat
B. Polarity
C. Cohesion
D. Adhesion
Answer: B
Rationale: Water's polarity—the partial positive charge
on hydrogen and partial negative charge on oxygen—
allows it to dissolve polar and ionic substances by
surrounding charged particles and separating them.
4. What is the pH of a neutral solution at 25°C?
A. 0
B. 5
C. 7
D. 14
Answer: C
Rationale: A neutral solution has a pH of 7, where the
concentration of hydrogen ions [H⁺] equals the
,https://www.stuvia.com/user/performance
concentration of hydroxide ions [OH⁻]. pH <7 is acidic; pH
>7 is basic.
5. Which macromolecule is the primary source of quick
energy for cells?
A. Protein
B. Lipid
C. Carbohydrate
D. Nucleic acid
Answer: C
Rationale: Carbohydrates (glucose, glycogen, starch) are
the primary source of quick energy. They are broken
down rapidly through cellular respiration to produce ATP.
6. What is the monomer of proteins?
A. Nucleotide
B. Monosaccharide
C. Amino acid
D. Fatty acid
Answer: C
Rationale: Proteins are polymers of amino acids linked by
peptide bonds. Nucleotides form nucleic acids;
monosaccharides form carbohydrates; fatty acids form
lipids.
7. What is the function of enzymes in biological systems?
A. To provide energy
, https://www.stuvia.com/user/performance
B. To act as biological catalysts, lowering activation energy
C. To store genetic information
D. To form cell membranes
Answer: B
Rationale: Enzymes are proteins that catalyze biochemical
reactions by lowering the activation energy required,
speeding up reactions without being consumed.
8. What is "denaturation" of a protein?
A. The synthesis of a protein
B. The loss of a protein's three-dimensional structure and
function due to heat, pH, or chemicals
C. The folding of a protein
D. The transport of a protein
Answer: B
Rationale: Denaturation disrupts the secondary, tertiary,
and quaternary structures of a protein, causing loss of
function. It can be caused by high temperature, extreme
pH, or chemicals. Primary structure (amino acid
sequence) remains intact.
9. Which organic molecule is the primary component of cell
membranes?
A. Carbohydrate
B. Phospholipid
C. Nucleic acid
