Free Lipids MCQs with Answers

1. Compared with carbohydrates, lipids yield more energy per gram because they

• A. contain more oxygen atoms per carbon
• B. are more highly reduced, with more carbon-hydrogen bonds per gram
• C. are soluble in water
• D. are broken down without any oxygen

Explanation: Energy is released when carbon-hydrogen bonds are oxidised, and a fatty acid chain is almost entirely carbon and hydrogen with very little oxygen already attached. Carbohydrates are partly oxidised to begin with, so less energy remains to be released, which is why fat yields about 9 kcal per gram against roughly 4 for carbohydrate. Lipids are insoluble in water and their breakdown is fully aerobic.

2. A phospholipid molecule is described as amphipathic because it has

• A. two hydrophobic ends
• B. a hydrophilic head and hydrophobic tails
• C. two hydrophilic ends
• D. no charged groups at all

Explanation: The phosphate head is charged and interacts with water, while the two fatty acid tails are non-polar and are excluded from it. Placed in water, the molecules therefore arrange themselves into a bilayer with the tails facing inward, which is the basis of every cell membrane. A molecule with only one kind of end could not form that structure.

3. An unsaturated fatty acid differs from a saturated one in that it

• A. contains one or more carbon to carbon double bonds in its hydrocarbon chain
• B. contains more hydrogen atoms per carbon
• C. has no carboxyl group
• D. cannot be used in respiration

Explanation: Each double bond puts a kink in the chain, so the molecules pack together less closely and the fat has a lower melting point, which is why plant oils are liquid while animal fats are solid at room temperature. Saturated means the chain carries the maximum possible hydrogen, so the unsaturated form has fewer hydrogens, not more. Diets high in saturated fat are linked with atherosclerosis.

4. Cholesterol is important in the human body because it

• A. is the main energy store of adipose tissue
• B. carries oxygen in the blood
• C. is the precursor of the steroid sex hormones, bile salts and vitamin D
• D. forms the walls of plant cells

Explanation: Cholesterol is a steroid and the starting material for testosterone, oestrogen, bile salts and vitamin D, and it also sits between the phospholipids of animal membranes and regulates their fluidity. Its bad reputation comes from the deposits it forms in artery walls when the blood level is high, not from any lack of function. Triglycerides, not cholesterol, are the energy store of adipose tissue.

5. A triglyceride is formed when glycerol combines with three fatty acids by

• A. hydrolysis, forming glycosidic bonds
• B. condensation, forming ester bonds and releasing three molecules of water
• C. oxidation, forming peptide bonds
• D. reduction, forming hydrogen bonds

Explanation: Each of the three hydroxyl groups of glycerol reacts with the carboxyl group of a fatty acid, so three ester bonds form and three water molecules are released. Digestion reverses this by hydrolysis, adding water back and freeing the fatty acids and glycerol for absorption. Glycosidic bonds join sugars and peptide bonds join amino acids, so neither term applies to a lipid.

6. Which lipid is a major component of cell membranes?

• A. Triglyceride
• B. Phospholipid
• C. Steroid
• D. Wax

Explanation: Phospholipids form the lipid bilayer of cell membranes due to their amphipathic nature (hydrophilic head, hydrophobic tails).

7. Which vitamin is fat-soluble?

• A. Vitamin C
• B. Vitamin B12
• C. Vitamin D
• D. Vitamin B6

Explanation: Vitamins A, D, E, and K are fat-soluble. Vitamin C and B vitamins are water-soluble.