Question 1

Which of the following best explains why phospholipids spontaneously form bilayers in aqueous environments?

Accepted Answer

Their amphipathic nature causes hydrophilic heads to interact with water and hydrophobic tails to avoid water.

Question 2

A researcher creates two artificial membranes: Membrane A is made of phospholipids with long, saturated hydrocarbon tails; Membrane B is made of phospholipids with short, unsaturated hydrocarbon tails. At room temperature, which membrane is more permeable to small polar molecules and why?

Accepted Answer

Membrane B, because short and unsaturated tails prevent tight packing, increasing permeability.

Question 3

Which of the following statements about triglycerides is correct?

Accepted Answer

Triglycerides are used primarily for long-term energy storage in cells.

Question 4

Which equation correctly represents the dehydration reaction that forms a triglyceride from glycerol and three fatty acids?

Accepted Answer

$\mathrm{Glycerol} + 3\ \mathrm{Fatty\ acids} \rightarrow \mathrm{Triglyceride} + 3\ \mathrm{H_2O}$

Question 5

Trans-fats are produced during food processing by hydrogenation. What is a major health concern associated with trans-fats?

Accepted Answer

They are associated with increased risk of cardiovascular disease.

Question 6

Which of the following changes would decrease the permeability of a cell membrane to polar molecules?

Accepted Answer

Increasing the length of hydrocarbon tails in phospholipids.

Question 7

A red blood cell is placed in a hypotonic solution such as distilled water. What will happen to the cell and why?

Accepted Answer

It will swell and may burst because water enters the cell by osmosis.

Question 8

Why can plant cells survive in hypotonic environments while animal cells may burst?

Accepted Answer

Plant cells have a rigid cell wall that prevents excessive swelling.

Question 9

Which of the following best describes the role of cholesterol in animal cell membranes?

Accepted Answer

Cholesterol acts as a fluidity buffer, increasing fluidity at low temperatures and decreasing it at high temperatures.

Question 10

Which of the following molecules would most easily cross a pure phospholipid bilayer without the help of a transport protein?

Accepted Answer

Oxygen ($\mathrm{O_2}$)

Question 11

Which process is responsible for the movement of water across a cell membrane from a region of low solute concentration to high solute concentration?

Accepted Answer

Osmosis

Question 12

A cell membrane contains a high proportion of unsaturated phospholipids. What effect does this have on membrane fluidity and permeability?

Accepted Answer

Increases fluidity and increases permeability.

Question 13

Which of the following best describes facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient through a protein channel or carrier, without energy input.

Question 14

The sodium-potassium pump ($\mathrm{Na^+/K^+}$-ATPase) moves ions against their concentration gradients. Which equation best represents the stoichiometry of this pump?

Accepted Answer

$3\ \mathrm{Na^+}$ out, $2\ \mathrm{K^+}$ in, per ATP hydrolyzed

Question 15

Which of the following is an example of secondary active transport?

Accepted Answer

Movement of glucose into a cell using the sodium gradient established by the sodium-potassium pump.

Question 16

Which of the following statements about membrane proteins is correct?

Accepted Answer

Integral (transmembrane) proteins can form channels or carriers for transport across the membrane.

Question 17

A mutation causes a cell to produce phospholipids with only saturated fatty acid tails. What is the most likely effect on the cell membrane at room temperature?

Accepted Answer

The membrane will become less fluid and less permeable.

Question 18

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

Accepted Answer

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

Question 19

Which of the following would most likely increase the rate of diffusion of a solute across a lipid bilayer?

Accepted Answer

Increasing the concentration gradient of the solute.

Lipids and Membranes: Structure, Function, and Transport

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