Question 1

Which structural feature of lipids is primarily responsible for their insolubility in water?

Accepted Answer

A high proportion of nonpolar C—C and C—H bonds

Question 2

A researcher creates two artificial membranes: Membrane A is made exclusively with a phospholipid that contains a long unsaturated hydrocarbon tail. Membrane B is made exclusively of a phospholipid in which the hydrocarbon tail is short and saturated. At room temperature, which membrane would be more fluid and which would allow water to pass through more readily?

Accepted Answer

Membrane A would be more fluid; Membrane A would allow water to pass more readily.

Question 3

Which of the following increases the strength of hydrophobic interactions in membranes and thus makes them less permeable to polar molecules?

Accepted Answer

Increasing the length of the hydrocarbon chains

Question 4

What is the primary role of fats (triacylglycerols) in cells?

Accepted Answer

Energy storage due to high-energy bonds in fatty acid chains

Question 5

Which part of a phospholipid molecule interacts with water when placed in an aqueous solution?

Accepted Answer

The polar phosphate-containing head group

Question 6

Why are phospholipids able to spontaneously form bilayers in water?

Accepted Answer

They are amphipathic, containing both hydrophilic heads and hydrophobic tails.

Question 7

Which of the following statements best describes the effect of cholesterol on membrane permeability?

Accepted Answer

Cholesterol decreases membrane permeability by increasing the density of the hydrophobic section.

Question 8

A planar bilayer contains equal amounts of saturated and unsaturated phospholipids. After measuring its permeability to glucose, you increase the proportion of unsaturated phospholipids. What will happen to the membrane’s permeability to glucose?

Accepted Answer

Permeability to glucose will increase.

Question 9

Region A has a low solute concentration. Region B has a high solute concentration. They are separated by a selectively permeable membrane that is impermeable to solute but allows passage of water. Which of the following is true?

Accepted Answer

Water moves from region A to region B via osmosis.

Question 10

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

Accepted Answer

The consumption of ATP to move sodium and potassium against their concentration gradients by the sodium-potassium pump

Question 11

Which equation best describes the net movement of molecules during diffusion?

Accepted Answer

$J = -D \frac{dC}{dx}$

Question 12

What is the main difference between facilitated diffusion and active transport?

Accepted Answer

Facilitated diffusion moves substances down their concentration gradient without energy input, while active transport moves substances against their gradient using energy.

Question 13

Which of the following best describes the amphipathic nature of transmembrane proteins?

Accepted Answer

Hydrophobic amino acids are found within the membrane interior, while hydrophilic amino acids are exposed to the aqueous environment.

Question 14

Which of the following transport processes is passive and requires a transport protein?

Accepted Answer

Facilitated diffusion

Question 15

What is the effect of decreasing temperature on membrane fluidity and permeability?

Accepted Answer

Membrane fluidity decreases, causing decreased permeability.

Question 16

Which of the following statements about the sodium-potassium pump ($Na^+/K^+$-ATPase) is correct?

Accepted Answer

It uses ATP to move $Na^+$ and $K^+$ ions against their concentration gradients.

Question 17

Secondary active transport (co-transport) relies on which of the following?

Accepted Answer

Electrochemical gradients established by primary active transport

Question 18

Which of the following best describes the fluid-mosaic model of membrane structure?

Accepted Answer

Membranes are dynamic mosaics of phospholipids and proteins, with some proteins spanning the membrane.

Question 19

Which of the following is NOT a function of lipids in cells?

Accepted Answer

Acting as enzymes to catalyze reactions

Chapter 6: Lipids, Membranes, and the First Cells – Structure, Function, and Biological Roles

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