Question 1

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

Accepted Answer

The hydrophilic heads interact with water, while the hydrophobic tails avoid it, minimizing free energy.

Question 2

Which of the following is NOT a major phospholipid found in eukaryotic cell membranes?

Accepted Answer

Triacylglycerol

Question 3

Cholesterol is an important component of animal cell membranes. What is its primary effect on membrane fluidity?

Accepted Answer

It decreases membrane fluidity at high temperatures and increases it at low temperatures.

Question 4

A sealed compartment formed by a phospholipid bilayer is energetically favorable because:

Accepted Answer

It minimizes the exposure of hydrophobic tails to water.

Question 5

Which property of unsaturated hydrocarbon chains in phospholipids most directly affects membrane fluidity?

Accepted Answer

The presence of cis-double bonds creates kinks, preventing tight packing.

Question 6

A researcher uses fluorescent dye to label phospholipids in a cell membrane. Over time, the dye spreads laterally but not vertically. What property of the membrane does this demonstrate?

Accepted Answer

Phospholipids undergo lateral diffusion within the same leaflet.

Question 7

Which of the following best describes the orientation of cholesterol in the plasma membrane?

Accepted Answer

Cholesterol's polar head aligns with the polar heads of phospholipids, and its rigid ring structure inserts among the fatty acid tails.

Question 8

Lipid rafts are specialized microdomains in the plasma membrane. Which of the following is TRUE about lipid rafts?

Accepted Answer

They are regions enriched in cholesterol and sphingolipids, often involved in cell signaling.

Question 9

Which equation best represents the relationship between the number of cholesterol molecules and phospholipids in a typical animal cell membrane?

Accepted Answer

$$n_{cholesterol} \approx n_{phospholipid}$$

Question 10

Which of the following statements about membrane proteins is correct?

Accepted Answer

Transmembrane proteins have both hydrophobic and hydrophilic regions.

Question 11

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

Accepted Answer

The membrane will become less fluid and more rigid.

Question 12

Which of the following best describes the role of lipid droplets in cells?

Accepted Answer

They store triacylglycerols and phospholipids for membrane synthesis and as an energy source.

Question 13

Which of the following scenarios would be energetically UNFAVORABLE for a phospholipid bilayer?

Accepted Answer

A planar bilayer with edges exposed to water.

Question 14

Which of the following is a consequence of the amphipathic nature of phospholipids?

Accepted Answer

They form micelles or bilayers in aqueous environments.

Question 15

Which of the following best explains why liposomes are used in drug delivery systems?

Accepted Answer

Liposomes can encapsulate hydrophilic drugs in their aqueous interior and hydrophobic drugs in their bilayer.

Question 16

A cell membrane contains phosphatidylcholine, sphingomyelin, and cholesterol. Which of the following is TRUE about their arrangement?

Accepted Answer

Phosphatidylcholine and sphingomyelin can cluster together to form lipid rafts enriched in cholesterol.

Question 17

Which of the following experimental techniques can be used to study the lateral mobility of lipids in membranes?

Accepted Answer

Fluorescent dye labeling and fluorescence recovery after photobleaching (FRAP)

Question 18

Which of the following is a correct statement about the structure of sphingomyelin?

Accepted Answer

It contains a sphingosine backbone.

Question 19

Which of the following best describes the difference between transmembrane and peripheral membrane proteins?

Accepted Answer

Transmembrane proteins span the lipid bilayer, while peripheral proteins associate with the membrane surface.

Question 20

If a cell is placed in a solution containing a fluorescently labeled phospholipid, which process would allow the label to appear on both leaflets of the bilayer over time?

Accepted Answer

Flip-flop movement mediated by flippase enzymes

Membrane Structure: Composition and Organization of Biological Membranes

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