Question 1

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

Accepted Answer

The hydrophilic heads interact with water while the hydrophobic tails avoid water, leading to bilayer formation.

Question 2

A researcher adds cholesterol to a synthetic phospholipid bilayer. What is the most likely effect on the membrane's permeability?

Accepted Answer

Permeability will decrease because cholesterol increases the packing density of the hydrophobic tails.

Question 3

Which of the following molecules would cross a pure phospholipid bilayer most rapidly?

Accepted Answer

A small nonpolar molecule such as $$\mathrm{O}_2$$

Question 4

A cell is placed in a hypertonic solution. What will happen to the cell and why?

Accepted Answer

The cell will shrink because water moves out of the cell.

Question 5

Which of the following statements about membrane proteins is correct according to the fluid-mosaic model?

Accepted Answer

Some proteins span the membrane and have both hydrophilic and hydrophobic regions.

Question 6

Which of the following best describes the difference between saturated and unsaturated fatty acids?

Accepted Answer

Unsaturated fatty acids have one or more double bonds, resulting in kinks that increase membrane fluidity.

Question 7

A mutation causes a cell to produce phospholipids with much longer saturated hydrocarbon tails. What is the most likely effect on the cell membrane?

Accepted Answer

The membrane will become less permeable and more rigid.

Question 8

Which of the following is an example of active transport across a membrane?

Accepted Answer

Movement of $$\mathrm{Na}^+$$ and $$\mathrm{K}^+$$ ions by the sodium-potassium pump using ATP.

Question 9

Which of the following best explains why facilitated diffusion does not require energy input?

Accepted Answer

It moves substances down their concentration gradient with the help of membrane proteins.

Question 10

A patient with cystic fibrosis has a defective CFTR protein. What is the direct consequence at the cellular level?

Accepted Answer

Chloride ions cannot leave the cell, leading to thick mucus secretions.

Question 11

Which of the following best describes the role of amphipathic molecules in membrane structure?

Accepted Answer

They have both hydrophilic and hydrophobic regions, allowing them to form bilayers.

Question 12

A vesicle containing a 0.2 M sucrose solution is placed in a beaker containing a 0.5 M sucrose solution. What will happen to the vesicle?

Accepted Answer

Water will move out of the vesicle, causing it to shrink.

Question 13

Which of the following equations best represents the movement of water during osmosis?

Accepted Answer

$$	ext{Water moves from regions of low solute concentration to high solute concentration}$$

Question 14

Which of the following is NOT a function of lipids in biological systems?

Accepted Answer

Acting as enzymes to catalyze reactions

Question 15

A scientist is studying a membrane protein that allows only potassium ions ($$\mathrm{K}^+) to $$pass through. What property of the protein is most responsible for this selectivity?

Accepted Answer

The specific arrangement of hydrophilic residues lining the pore

Question 16

Which of the following best describes secondary active transport (co-transport)?

Accepted Answer

It uses the energy stored in an electrochemical gradient to move another molecule against its gradient.

Question 17

Which of the following changes would most likely increase the fluidity of a cell membrane at room temperature?

Accepted Answer

Increasing the proportion of unsaturated fatty acids in phospholipids

Question 18

Which of the following statements about the sodium-potassium pump is correct?

Accepted Answer

It requires ATP to transport ions against their concentration gradients.

Question 19

A cell membrane is composed of phospholipids with short, unsaturated hydrocarbon tails. Which of the following is most likely true about this membrane?

Accepted Answer

It will have high permeability to small molecules.

Question 20

Which of the following best explains why liposomes are useful experimental systems for studying membrane permeability?

Accepted Answer

They are artificial vesicles with controlled lipid composition, allowing precise measurement of permeability.

Lipids, Membranes, and the First Cells: Chapter 6 Study Guide

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