ACS BIOCHEMISTRY QUESTION
BANK 2026 FULL SOLUTIONS
GRADED A+
◉ Properties of cells
Answer: Metabolism: undergoing catabolic and anabolic processes.
Reproduction: cell populations grow via asexual reproduction.
Mutation: during growth and reproduction, cells sometimes make
mistakes, leading to mutations and evolution.
Respond to environment: metabolic pathways respond to signals,
including light, touch, hormones, and nutrients, that can turn the
pathways on or off.
Speed and efficiency: cell operations are highly specific to maximize
targeting and efficiency.
Similar building blocks: most species are very similar at the cellular
level.
◉ What accounts for water's unique properties?
Answer: Hydrogen bonding
,◉ The unique properties of water (specific heat, heat of vaporization,
solubility)
Answer: 1) high specific heat, or heat required to raise the temperature
of the unit mass of a given substance by one degree.
For water to increase in temperature, water molecules must be made to
move faster, or get higher KE, and doing this requires breaking
hydrogen bonds, which absorbs heat. So, as heat is applied, most of it
goes to breaking the bonds not upregulating KE, thus making water
harder to heat than substances where no bonds need to be broken.
2) High heat of vaporization, or the amount of heat needed to turn one g
of a liquid into vapor, without a temperature rise in the liquid. Important
for sweat because it ensures that when the liquid evaporates from our
skin, the heat required for the transition is kept in the gas, causing a net
cooling effect on the skin.
3) Unique solubility properties: "like dissolves like". Water dissolves
polar molecules and ions, and can act as an H-bond donor or receptor
4) Amphoteric, it can act as an acid (donating electrons) or a base
(accepting electrons). The conjugate acid of water is the hydronium ion,
H3O+, and the conjugate base of water is the hydroxide ion, OH-.
◉ Keq for water at 25 degrees C and in pure water
Answer: At 25 degrees C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
,In pure water:
[OH-]=[H3O+]= 1*10^-7
◉ Calculation for pH and pKa
Answer: pH= -log[H3O+]
pKa= -log(Ka)
◉ Normal blood pH range
Answer: 7.35-7.45
◉ The Hydrophobic Effect
Answer: When non-polar molecules aggregate in the presence of water,
minimizing the entropy decrease water must go through to order
themselves around the border of the non-polar molecule. Reducing the
surface area water must organize around increases entropy, which is
favorable.
The aggregation is responsible for the formation of a variety of lipid
structures in the body, including cell membranes.
◉ Buffers
Answer: Composed of a weak acid (HA) and its conjugate base (A-).
Added acid reacts with A-, and added base reacts with HA, giving a
limited overall pH change.
, Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
◉ When are buffers optimal? What equation can we use for this?
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
◉ Blood Buffering
Answer: Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and
water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
BANK 2026 FULL SOLUTIONS
GRADED A+
◉ Properties of cells
Answer: Metabolism: undergoing catabolic and anabolic processes.
Reproduction: cell populations grow via asexual reproduction.
Mutation: during growth and reproduction, cells sometimes make
mistakes, leading to mutations and evolution.
Respond to environment: metabolic pathways respond to signals,
including light, touch, hormones, and nutrients, that can turn the
pathways on or off.
Speed and efficiency: cell operations are highly specific to maximize
targeting and efficiency.
Similar building blocks: most species are very similar at the cellular
level.
◉ What accounts for water's unique properties?
Answer: Hydrogen bonding
,◉ The unique properties of water (specific heat, heat of vaporization,
solubility)
Answer: 1) high specific heat, or heat required to raise the temperature
of the unit mass of a given substance by one degree.
For water to increase in temperature, water molecules must be made to
move faster, or get higher KE, and doing this requires breaking
hydrogen bonds, which absorbs heat. So, as heat is applied, most of it
goes to breaking the bonds not upregulating KE, thus making water
harder to heat than substances where no bonds need to be broken.
2) High heat of vaporization, or the amount of heat needed to turn one g
of a liquid into vapor, without a temperature rise in the liquid. Important
for sweat because it ensures that when the liquid evaporates from our
skin, the heat required for the transition is kept in the gas, causing a net
cooling effect on the skin.
3) Unique solubility properties: "like dissolves like". Water dissolves
polar molecules and ions, and can act as an H-bond donor or receptor
4) Amphoteric, it can act as an acid (donating electrons) or a base
(accepting electrons). The conjugate acid of water is the hydronium ion,
H3O+, and the conjugate base of water is the hydroxide ion, OH-.
◉ Keq for water at 25 degrees C and in pure water
Answer: At 25 degrees C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
,In pure water:
[OH-]=[H3O+]= 1*10^-7
◉ Calculation for pH and pKa
Answer: pH= -log[H3O+]
pKa= -log(Ka)
◉ Normal blood pH range
Answer: 7.35-7.45
◉ The Hydrophobic Effect
Answer: When non-polar molecules aggregate in the presence of water,
minimizing the entropy decrease water must go through to order
themselves around the border of the non-polar molecule. Reducing the
surface area water must organize around increases entropy, which is
favorable.
The aggregation is responsible for the formation of a variety of lipid
structures in the body, including cell membranes.
◉ Buffers
Answer: Composed of a weak acid (HA) and its conjugate base (A-).
Added acid reacts with A-, and added base reacts with HA, giving a
limited overall pH change.
, Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
◉ When are buffers optimal? What equation can we use for this?
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
◉ Blood Buffering
Answer: Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and
water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
