Question 1

Which of the following best explains why lipids do NOT form classic biopolymers like proteins and nucleic acids?

Accepted Answer

Lipids are assembled by the hydrophobic effect and weak intermolecular forces, not by covalent polymerization.

Question 2

Which structural feature of unsaturated fatty acids most directly leads to a lower melting temperature compared to saturated fatty acids?

Accepted Answer

Presence of cis-double bonds that introduce kinks, preventing tight packing.

Question 3

A cell membrane is composed of phospholipids with long, saturated hydrocarbon tails. What effect would this have on membrane permeability and fluidity at room temperature?

Accepted Answer

Lower permeability and decreased fluidity due to tight packing of tails.

Question 4

Which of the following is a primary function of triglycerides (fats and oils) in biological systems?

Accepted Answer

Energy storage due to their compact, hydrophobic structure.

Question 5

Why do fat deposits in animals contain almost no water, and what is the biological consequence of this?

Accepted Answer

Fat molecules are non-polar and interact poorly with water, allowing for dense energy storage without water weight.

Question 6

Which of the following best describes the amphipathic nature of phospholipids?

Accepted Answer

They have both hydrophilic head groups and hydrophobic tails.

Question 7

What is the main driving force for the self-assembly of lipid bilayers in aqueous environments?

Accepted Answer

Hydrophobic effect, which minimizes the ordering of water molecules around non-polar tails.

Question 8

Which of the following changes would increase the permeability of a phospholipid bilayer to small, non-polar molecules?

Accepted Answer

Increasing the number of double bonds in the hydrocarbon tails.

Question 9

A red blood cell is placed in pure water. Predict what will happen and explain the underlying process.

Accepted Answer

The cell will swell and potentially burst as water enters by osmosis.

Question 10

Which of the following best describes the difference between passive and active transport across cell membranes?

Accepted Answer

Passive transport moves molecules down their concentration gradient without energy input; active transport moves molecules against their gradient using energy.

Question 11

Which equation best represents the process of saponification, the production of soap from fats?

Accepted Answer

$$\mathrm{Fat} + 3\ \mathrm{NaOH} \rightarrow \mathrm{Glycerol} + 3\ \mathrm{Soap\ (fatty\ acid\ salts)}$$

Question 12

Which of the following statements about cholesterol in cell membranes is correct?

Accepted Answer

Cholesterol increases membrane fluidity at low temperatures but stabilizes (decreases fluidity) at high temperatures.

Question 13

Which of the following best describes the movement of phospholipids within a membrane?

Accepted Answer

Phospholipids can diffuse laterally within a leaflet, contributing to membrane fluidity.

Question 14

A cold-adapted insect living in Antarctica has cell membranes with phospholipids that differ from those of a temperate insect. What would you predict about the phospholipid composition of the Antarctic insect?

Accepted Answer

Shorter and more unsaturated hydrocarbon tails to maintain membrane fluidity at low temperatures.

Question 15

Which of the following best describes the electrochemical gradient across a cell membrane?

Accepted Answer

It is the combined effect of concentration and charge differences of ions across the membrane.

Question 16

Which of the following is true about facilitated diffusion?

Accepted Answer

It allows specific molecules to cross the membrane down their concentration gradient via a protein channel or carrier.

Question 17

Which of the following is a correct statement about the sodium-potassium pump (Na+/K+-ATPase)?

Accepted Answer

It uses energy from ATP hydrolysis to move sodium and potassium ions against their concentration gradients.

Question 18

Which of the following would most likely increase the rate of passive diffusion of a small, non-polar molecule across a cell membrane?

Accepted Answer

Increasing the temperature.

Question 19

A solution is described as hypertonic relative to a cell. What will happen to the cell when placed in this solution?

Accepted Answer

The cell will shrink as water leaves.

Lipids and Membranes: Structure, Function, and Transport

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