C785 Biochemistry Module 2: Water, pH, and Amino Acids 2026
|WGU
1. Which property of water allows it to act as a universal solvent for polar
substances?
A. Its high specific heat capacity
B. Its ability to form ionic bonds
C. Its polar nature and ability to form hydrogen bonds
D. Its low density in solid form
Answer: C
Rationale: Water is a polar molecule with a partial negative charge on oxygen and partial
positive charges on hydrogen, allowing it to dissolve other polar and ionic substances via
hydrogen bonding and electrostatic interactions.
2. What is the primary bond type responsible for the unique properties of
water, such as cohesion and surface tension?
A. Covalent bonds
B. Ionic bonds
C. Hydrogen bonds
D. Hydrophobic interactions
Answer: C
Rationale: Hydrogen bonds form between the slightly positive hydrogen of one water
molecule and the slightly negative oxygen of another, creating the sticky quality known as
cohesion.
,3. In the context of pH, a substance that increases the concentration of
hydrogen ions (H+) in a solution is known as a(n):
A. Base
B. Acid
C. Isotope
D. Buffer
Answer: B
Rationale: Acids are proton donors that release H+ ions into a solution, thereby lowering
the pH.
4. A solution with a pH of 4 is how many times more acidic than a solution with
a pH of 6?
A. 2 times
B. 20 times
C. 100 times
D. 1000 times
Answer: C
Rationale: The pH scale is logarithmic. Each unit represents a 10-fold difference in H+
concentration. A difference of 2 units (6 - 4) equals 10^2, or 100 times.
5. What is the primary function of a buffer system in biological fluids?
A. To increase the rate of chemical reactions
B. To provide energy for cellular metabolism
C. To maintain a constant pH by resisting changes
D. To transport oxygen to tissues
Answer: C
Rationale: Buffers consist of a weak acid and its conjugate base, which work together to
neutralize small amounts of added acid or base, maintaining pH stability.
, 6. Which part of an amino acid’s structure determines its unique chemical
properties?
A. The side chain (R-group)
B. The carboxyl group
C. The amino group
D. The alpha-carbon atom
Answer: A
Rationale: While all amino acids share a common backbone (amino, carboxyl, and alpha-
carbon), the R-group varies for each of the 20 amino acids and determines its behavior.
7. Which of the following amino acids is classified as non-polar (hydrophobic)?
A. Leucine
B. Serine
C. Aspartic Acid
D. Lysine
Answer: A
Rationale: Leucine has an aliphatic hydrocarbon side chain, making it hydrophobic. Serine
is polar, Aspartic Acid is acidic/negative, and Lysine is basic/positive.
8. At physiological pH (around 7.4), the carboxyl group of an amino acid is
typically:
A. Protonated and neutral
B. Protonated and positively charged
C. Deprotonated and negatively charged
D. Deprotonated and neutral
Answer: C
Rationale: At pH 7.4, the carboxyl group (pKa ~2) has lost its proton to become COO-,
carrying a negative charge.
|WGU
1. Which property of water allows it to act as a universal solvent for polar
substances?
A. Its high specific heat capacity
B. Its ability to form ionic bonds
C. Its polar nature and ability to form hydrogen bonds
D. Its low density in solid form
Answer: C
Rationale: Water is a polar molecule with a partial negative charge on oxygen and partial
positive charges on hydrogen, allowing it to dissolve other polar and ionic substances via
hydrogen bonding and electrostatic interactions.
2. What is the primary bond type responsible for the unique properties of
water, such as cohesion and surface tension?
A. Covalent bonds
B. Ionic bonds
C. Hydrogen bonds
D. Hydrophobic interactions
Answer: C
Rationale: Hydrogen bonds form between the slightly positive hydrogen of one water
molecule and the slightly negative oxygen of another, creating the sticky quality known as
cohesion.
,3. In the context of pH, a substance that increases the concentration of
hydrogen ions (H+) in a solution is known as a(n):
A. Base
B. Acid
C. Isotope
D. Buffer
Answer: B
Rationale: Acids are proton donors that release H+ ions into a solution, thereby lowering
the pH.
4. A solution with a pH of 4 is how many times more acidic than a solution with
a pH of 6?
A. 2 times
B. 20 times
C. 100 times
D. 1000 times
Answer: C
Rationale: The pH scale is logarithmic. Each unit represents a 10-fold difference in H+
concentration. A difference of 2 units (6 - 4) equals 10^2, or 100 times.
5. What is the primary function of a buffer system in biological fluids?
A. To increase the rate of chemical reactions
B. To provide energy for cellular metabolism
C. To maintain a constant pH by resisting changes
D. To transport oxygen to tissues
Answer: C
Rationale: Buffers consist of a weak acid and its conjugate base, which work together to
neutralize small amounts of added acid or base, maintaining pH stability.
, 6. Which part of an amino acid’s structure determines its unique chemical
properties?
A. The side chain (R-group)
B. The carboxyl group
C. The amino group
D. The alpha-carbon atom
Answer: A
Rationale: While all amino acids share a common backbone (amino, carboxyl, and alpha-
carbon), the R-group varies for each of the 20 amino acids and determines its behavior.
7. Which of the following amino acids is classified as non-polar (hydrophobic)?
A. Leucine
B. Serine
C. Aspartic Acid
D. Lysine
Answer: A
Rationale: Leucine has an aliphatic hydrocarbon side chain, making it hydrophobic. Serine
is polar, Aspartic Acid is acidic/negative, and Lysine is basic/positive.
8. At physiological pH (around 7.4), the carboxyl group of an amino acid is
typically:
A. Protonated and neutral
B. Protonated and positively charged
C. Deprotonated and negatively charged
D. Deprotonated and neutral
Answer: C
Rationale: At pH 7.4, the carboxyl group (pKa ~2) has lost its proton to become COO-,
carrying a negative charge.
