,CHEM 210 Module 6 Exam | Biochemistry |
Portage Learning | Q & A | 2026 Edition
1. Which of the following best defines a lipid?
A) A polymer of amino acids linked by peptide bonds
B) A water-soluble macromolecule that forms cell membranes
C) A hydrophobic or amphipathic biomolecule soluble in nonpolar solvents
D) A carbohydrate derivative that stores genetic information
Correct Answer: A hydrophobic or amphipathic biomolecule soluble in nonpolar solvents
Rationale: Lipids are defined by their solubility in nonpolar organic solvents rather than by a specific
chemical structure. They include fats, oils, steroids, phospholipids, and waxes. They are hydrophobic or
amphipathic, unlike proteins (amino acid polymers) or carbohydrates.
2. What is the primary function of triacylglycerols in the human body?
A) To form the structural framework of cell membranes
B) To serve as the primary storage form of energy in adipose tissue
C) To act as signaling molecules in inflammatory responses
D) To transport oxygen in the bloodstream
Correct Answer: To serve as the primary storage form of energy in adipose tissue
Rationale: Triacylglycerols (triglycerides) are the main storage form of energy in the body, stored in
adipose tissue. They provide more than twice the energy per gram compared to carbohydrates or
proteins. They are not major membrane components (phospholipids are), nor are they primary signaling
molecules or oxygen transporters.
3. According to the fluid mosaic model, which statement about membrane structure is correct?
A) Membrane proteins are fixed in place and do not move laterally
,B) The lipid bilayer is rigid and impermeable to all molecules
C) Phospholipids and proteins can diffuse laterally within the membrane bilayer
D) Cholesterol is absent from all biological membranes
Correct Answer: Phospholipids and proteins can diffuse laterally within the membrane bilayer
Rationale: The fluid mosaic model describes membranes as a fluid lipid bilayer in which phospholipids
and proteins can move laterally. This fluidity allows membrane proteins to function and membranes to
be dynamic. Membranes are selectively permeable, and cholesterol is a key component of animal cell
membranes.
4. Which type of lipid is completely hydrophobic and contains no polar head group?
A) Phospholipid
B) Triacylglycerol
C) Sphingolipid
D) Ganglioside
Correct Answer: Triacylglycerol
Rationale: Triacylglycerols consist of three fatty acids esterified to a glycerol backbone. They have no
charged or polar head group, making them completely hydrophobic (neutral, nonpolar). Phospholipids,
sphingolipids, and gangliosides all contain polar head groups and are amphipathic.
5. What is the backbone molecule used in the formation of storage fats (triacylglycerols)?
A) Ceramide
B) Glucose
C) Glycerol
D) Sphingosine
Correct Answer: Glycerol
, Rationale: Glycerol is the three-carbon backbone molecule to which three fatty acids are esterified to
form triacylglycerols (storage fats). Ceramide and sphingosine are backbones for sphingolipids, not
storage fats.
6. What is the role of cholesterol in animal cell membranes?
A) To provide energy for membrane transport processes
B) To increase membrane fluidity at low temperatures and decrease it at high temperatures
C) To form the primary structural framework of the membrane bilayer
D) To catalyze chemical reactions within the membrane
Correct Answer: To increase membrane fluidity at low temperatures and decrease it at high
temperatures
Rationale: Cholesterol acts as a membrane fluidity buffer. At low temperatures, it prevents fatty acid
chains from packing too tightly, maintaining fluidity. At high temperatures, it restricts excessive
movement of phospholipids, reducing fluidity.
7. Which of the following fatty acids is considered essential in humans?
A) Palmitic acid (16:0)
B) Linoleic acid (18:2 Δ⁹,¹²)
C) Stearic acid (18:0)
D) Oleic acid (18:1 Δ⁹)
Correct Answer: Linoleic acid (18:2 Δ⁹,¹²)
Rationale: Linoleic acid is an essential omega-6 fatty acid that humans cannot synthesize and must
obtain from the diet. It is a precursor for arachidonic acid and other important signaling molecules.
Palmitic, stearic, and oleic acids can be synthesized by the body.
8. In a sphingolipid, what serves as the backbone to which fatty acids and head groups are attached?
Portage Learning | Q & A | 2026 Edition
1. Which of the following best defines a lipid?
A) A polymer of amino acids linked by peptide bonds
B) A water-soluble macromolecule that forms cell membranes
C) A hydrophobic or amphipathic biomolecule soluble in nonpolar solvents
D) A carbohydrate derivative that stores genetic information
Correct Answer: A hydrophobic or amphipathic biomolecule soluble in nonpolar solvents
Rationale: Lipids are defined by their solubility in nonpolar organic solvents rather than by a specific
chemical structure. They include fats, oils, steroids, phospholipids, and waxes. They are hydrophobic or
amphipathic, unlike proteins (amino acid polymers) or carbohydrates.
2. What is the primary function of triacylglycerols in the human body?
A) To form the structural framework of cell membranes
B) To serve as the primary storage form of energy in adipose tissue
C) To act as signaling molecules in inflammatory responses
D) To transport oxygen in the bloodstream
Correct Answer: To serve as the primary storage form of energy in adipose tissue
Rationale: Triacylglycerols (triglycerides) are the main storage form of energy in the body, stored in
adipose tissue. They provide more than twice the energy per gram compared to carbohydrates or
proteins. They are not major membrane components (phospholipids are), nor are they primary signaling
molecules or oxygen transporters.
3. According to the fluid mosaic model, which statement about membrane structure is correct?
A) Membrane proteins are fixed in place and do not move laterally
,B) The lipid bilayer is rigid and impermeable to all molecules
C) Phospholipids and proteins can diffuse laterally within the membrane bilayer
D) Cholesterol is absent from all biological membranes
Correct Answer: Phospholipids and proteins can diffuse laterally within the membrane bilayer
Rationale: The fluid mosaic model describes membranes as a fluid lipid bilayer in which phospholipids
and proteins can move laterally. This fluidity allows membrane proteins to function and membranes to
be dynamic. Membranes are selectively permeable, and cholesterol is a key component of animal cell
membranes.
4. Which type of lipid is completely hydrophobic and contains no polar head group?
A) Phospholipid
B) Triacylglycerol
C) Sphingolipid
D) Ganglioside
Correct Answer: Triacylglycerol
Rationale: Triacylglycerols consist of three fatty acids esterified to a glycerol backbone. They have no
charged or polar head group, making them completely hydrophobic (neutral, nonpolar). Phospholipids,
sphingolipids, and gangliosides all contain polar head groups and are amphipathic.
5. What is the backbone molecule used in the formation of storage fats (triacylglycerols)?
A) Ceramide
B) Glucose
C) Glycerol
D) Sphingosine
Correct Answer: Glycerol
, Rationale: Glycerol is the three-carbon backbone molecule to which three fatty acids are esterified to
form triacylglycerols (storage fats). Ceramide and sphingosine are backbones for sphingolipids, not
storage fats.
6. What is the role of cholesterol in animal cell membranes?
A) To provide energy for membrane transport processes
B) To increase membrane fluidity at low temperatures and decrease it at high temperatures
C) To form the primary structural framework of the membrane bilayer
D) To catalyze chemical reactions within the membrane
Correct Answer: To increase membrane fluidity at low temperatures and decrease it at high
temperatures
Rationale: Cholesterol acts as a membrane fluidity buffer. At low temperatures, it prevents fatty acid
chains from packing too tightly, maintaining fluidity. At high temperatures, it restricts excessive
movement of phospholipids, reducing fluidity.
7. Which of the following fatty acids is considered essential in humans?
A) Palmitic acid (16:0)
B) Linoleic acid (18:2 Δ⁹,¹²)
C) Stearic acid (18:0)
D) Oleic acid (18:1 Δ⁹)
Correct Answer: Linoleic acid (18:2 Δ⁹,¹²)
Rationale: Linoleic acid is an essential omega-6 fatty acid that humans cannot synthesize and must
obtain from the diet. It is a precursor for arachidonic acid and other important signaling molecules.
Palmitic, stearic, and oleic acids can be synthesized by the body.
8. In a sphingolipid, what serves as the backbone to which fatty acids and head groups are attached?
