MCAT Biology Practice | 170 Questions with
Correct Answers and Rationale | Graded + |
2026-2027 Update
Question 1
The chemical reaction that breaks down all the major macromolecules is called:
A. Dehydration synthesis
B. Hydrolysis
C. Condensation
D. Oxidation
Correct Answer: B. Hydrolysis
Rationale: Hydrolysis is the chemical reaction that breaks down macromolecules
by adding water. The term "hydrolysis" literally means "water splitting" (hydro =
water, lysis = splitting). This process is essential for digestion and the breakdown
of proteins, carbohydrates, lipids, and nucleic acids into their monomeric
subunits. Dehydration synthesis (A) and condensation (C) are the opposite
reactions—they build macromolecules by removing water. Oxidation (D) involves
electron transfer.
Question 2
What is the strongest type of INTERmolecular bonds?
A. Van der Waals forces
B. Dipole-dipole bonds
C. Hydrogen bonds
D. Ionic bonds
Correct Answer: C. Hydrogen bonds
,Rationale: Hydrogen bonds are the strongest type of intermolecular forces. They
occur when a hydrogen atom bonded to a highly electronegative atom (O, N, or F)
is attracted to another electronegative atom. Dipole-dipole bonds (B) are weaker
than hydrogen bonds. Van der Waals forces (A) are the weakest intermolecular
forces. Ionic bonds (D) are intramolecular bonds (within molecules), not
intermolecular.
Question 3
Why is water a liquid at high temperatures?
A. Water has low molecular weight
B. Hydrogen bonding bonds water molecules closer together
C. Water is nonpolar
D. Water has weak intermolecular forces
Correct Answer: B. Hydrogen bonding bonds water molecules closer together
Rationale: Hydrogen bonding between water molecules pulls them closer
together, requiring more energy (higher temperature) to break these bonds and
convert water to a gas. This results in water having an unusually high boiling point
compared to other molecules of similar molecular weight. Water is polar (C is
wrong) and has strong intermolecular forces (D is wrong).
Question 4
What is an amphipathic molecule? Give an example.
A. A molecule with only hydrophobic regions; Example: Cholesterol
B. A molecule with only hydrophilic regions; Example: Glucose
C. A molecule with both hydrophobic and hydrophilic regions; Example:
Phospholipid
D. A molecule with no polar regions; Example: Oil
Correct Answer: C. A molecule with both hydrophobic and hydrophilic regions;
Example: Phospholipid
,Rationale: An amphipathic (or amphiphilic) molecule contains both hydrophobic
(water-fearing) and hydrophilic (water-loving) regions. Phospholipids are the
classic example—they have a hydrophilic phosphate head and hydrophobic fatty
acid tails. This property allows them to form bilayers that make up cell
membranes. Cholesterol (A) is mostly hydrophobic. Glucose (B) is hydrophilic. Oil
(D) is hydrophobic.
Question 5
What is a lipid?
A. A biological molecule with high solubility in water
B. A biological molecule with low solubility in water
C. A protein that catalyzes reactions
D. A carbohydrate that stores energy
Correct Answer: B. A biological molecule with low solubility in water
Rationale: Lipids are biological molecules characterized by low solubility in water
(hydrophobic). The term "lipid" means fat. Lipids include fats, oils, waxes,
phospholipids, and steroids. They are not water-soluble because they are
predominantly nonpolar hydrocarbons. Peptides and proteins (C) are not lipids.
Carbohydrates (D) are generally water-soluble.
Question 6
What are the 6 major groups of lipids?
A. Fatty acids, triglycerides, phospholipids, glycolipids, steroids, terpenes
B. Amino acids, carbohydrates, nucleic acids, proteins, vitamins, minerals
C. Monosaccharides, disaccharides, polysaccharides, oligosaccharides,
glycoproteins, proteoglycans
D. Enzymes, hormones, antibodies, neurotransmitters, growth factors, cytokines
Correct Answer: A. Fatty acids, triglycerides, phospholipids, glycolipids, steroids,
terpenes
, Rationale: The six major groups of lipids are: (1) fatty acids, (2) triglycerides
(triacylglycerols) with a 3-carbon glycerol backbone, (3) phospholipids, (4)
glycolipids, (5) steroids (4-ring structures), and (6) terpenes (large class of organic
compounds including essential oils, vitamin A, and plant pigments). The other
options list non-lipid biological molecules.
Question 7
What is the structure of a triglyceride?
A. A glycerol backbone with 3 fatty acid chains attached by ester bonds
B. A glycerol backbone with 2 fatty acid chains and a phosphate group
C. A glucose molecule with fatty acid chains
D. A 4-ring steroid structure with hydrocarbon chains
Correct Answer: A. A glycerol backbone with 3 fatty acid chains attached by
ester bonds
Rationale: Triglycerides (triacylglycerols) are esters composed of a 3-carbon
glycerol backbone with three fatty acid chains dangling from it. Each carbon chain
is attached by an ester bond formed between the glycerol hydroxyl group and the
fatty acid carboxyl group. Phospholipids (B) have 2 fatty acid chains and a
phosphate group. Steroids (D) have a 4-ring structure.
Question 8
What happens if you add water to an ester group in a triglyceride? How is this
reaction rate increased?
A. Water cleaves the ester bond into an alcohol and a carboxylic/fatty acid; Lipases
speed up this reaction
B. Water forms a new ester bond; Lipases inhibit the reaction
C. Water creates a double bond; Dehydrogenases speed up the reaction
D. Water removes a carboxyl group; Decarboxylases speed up the reaction
Correct Answer: A. Water cleaves the ester bond into an alcohol and a
carboxylic/fatty acid; Lipases speed up this reaction
Correct Answers and Rationale | Graded + |
2026-2027 Update
Question 1
The chemical reaction that breaks down all the major macromolecules is called:
A. Dehydration synthesis
B. Hydrolysis
C. Condensation
D. Oxidation
Correct Answer: B. Hydrolysis
Rationale: Hydrolysis is the chemical reaction that breaks down macromolecules
by adding water. The term "hydrolysis" literally means "water splitting" (hydro =
water, lysis = splitting). This process is essential for digestion and the breakdown
of proteins, carbohydrates, lipids, and nucleic acids into their monomeric
subunits. Dehydration synthesis (A) and condensation (C) are the opposite
reactions—they build macromolecules by removing water. Oxidation (D) involves
electron transfer.
Question 2
What is the strongest type of INTERmolecular bonds?
A. Van der Waals forces
B. Dipole-dipole bonds
C. Hydrogen bonds
D. Ionic bonds
Correct Answer: C. Hydrogen bonds
,Rationale: Hydrogen bonds are the strongest type of intermolecular forces. They
occur when a hydrogen atom bonded to a highly electronegative atom (O, N, or F)
is attracted to another electronegative atom. Dipole-dipole bonds (B) are weaker
than hydrogen bonds. Van der Waals forces (A) are the weakest intermolecular
forces. Ionic bonds (D) are intramolecular bonds (within molecules), not
intermolecular.
Question 3
Why is water a liquid at high temperatures?
A. Water has low molecular weight
B. Hydrogen bonding bonds water molecules closer together
C. Water is nonpolar
D. Water has weak intermolecular forces
Correct Answer: B. Hydrogen bonding bonds water molecules closer together
Rationale: Hydrogen bonding between water molecules pulls them closer
together, requiring more energy (higher temperature) to break these bonds and
convert water to a gas. This results in water having an unusually high boiling point
compared to other molecules of similar molecular weight. Water is polar (C is
wrong) and has strong intermolecular forces (D is wrong).
Question 4
What is an amphipathic molecule? Give an example.
A. A molecule with only hydrophobic regions; Example: Cholesterol
B. A molecule with only hydrophilic regions; Example: Glucose
C. A molecule with both hydrophobic and hydrophilic regions; Example:
Phospholipid
D. A molecule with no polar regions; Example: Oil
Correct Answer: C. A molecule with both hydrophobic and hydrophilic regions;
Example: Phospholipid
,Rationale: An amphipathic (or amphiphilic) molecule contains both hydrophobic
(water-fearing) and hydrophilic (water-loving) regions. Phospholipids are the
classic example—they have a hydrophilic phosphate head and hydrophobic fatty
acid tails. This property allows them to form bilayers that make up cell
membranes. Cholesterol (A) is mostly hydrophobic. Glucose (B) is hydrophilic. Oil
(D) is hydrophobic.
Question 5
What is a lipid?
A. A biological molecule with high solubility in water
B. A biological molecule with low solubility in water
C. A protein that catalyzes reactions
D. A carbohydrate that stores energy
Correct Answer: B. A biological molecule with low solubility in water
Rationale: Lipids are biological molecules characterized by low solubility in water
(hydrophobic). The term "lipid" means fat. Lipids include fats, oils, waxes,
phospholipids, and steroids. They are not water-soluble because they are
predominantly nonpolar hydrocarbons. Peptides and proteins (C) are not lipids.
Carbohydrates (D) are generally water-soluble.
Question 6
What are the 6 major groups of lipids?
A. Fatty acids, triglycerides, phospholipids, glycolipids, steroids, terpenes
B. Amino acids, carbohydrates, nucleic acids, proteins, vitamins, minerals
C. Monosaccharides, disaccharides, polysaccharides, oligosaccharides,
glycoproteins, proteoglycans
D. Enzymes, hormones, antibodies, neurotransmitters, growth factors, cytokines
Correct Answer: A. Fatty acids, triglycerides, phospholipids, glycolipids, steroids,
terpenes
, Rationale: The six major groups of lipids are: (1) fatty acids, (2) triglycerides
(triacylglycerols) with a 3-carbon glycerol backbone, (3) phospholipids, (4)
glycolipids, (5) steroids (4-ring structures), and (6) terpenes (large class of organic
compounds including essential oils, vitamin A, and plant pigments). The other
options list non-lipid biological molecules.
Question 7
What is the structure of a triglyceride?
A. A glycerol backbone with 3 fatty acid chains attached by ester bonds
B. A glycerol backbone with 2 fatty acid chains and a phosphate group
C. A glucose molecule with fatty acid chains
D. A 4-ring steroid structure with hydrocarbon chains
Correct Answer: A. A glycerol backbone with 3 fatty acid chains attached by
ester bonds
Rationale: Triglycerides (triacylglycerols) are esters composed of a 3-carbon
glycerol backbone with three fatty acid chains dangling from it. Each carbon chain
is attached by an ester bond formed between the glycerol hydroxyl group and the
fatty acid carboxyl group. Phospholipids (B) have 2 fatty acid chains and a
phosphate group. Steroids (D) have a 4-ring structure.
Question 8
What happens if you add water to an ester group in a triglyceride? How is this
reaction rate increased?
A. Water cleaves the ester bond into an alcohol and a carboxylic/fatty acid; Lipases
speed up this reaction
B. Water forms a new ester bond; Lipases inhibit the reaction
C. Water creates a double bond; Dehydrogenases speed up the reaction
D. Water removes a carboxyl group; Decarboxylases speed up the reaction
Correct Answer: A. Water cleaves the ester bond into an alcohol and a
carboxylic/fatty acid; Lipases speed up this reaction
