Question 1

Which of the following best describes the structure of a phospholipid molecule in a biological membrane?

Accepted Answer

The head region is polar and the tail region is non-polar.

Question 2

What is the primary reason that phospholipids spontaneously form bilayers in aqueous environments?

Accepted Answer

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

Question 3

Which type of molecule would most easily pass through a pure phospholipid bilayer without the aid of membrane proteins?

Accepted Answer

Non-polar molecules such as $O_2$ and hydrocarbons.

Question 4

How does the presence of double bonds in the hydrocarbon tails of phospholipids affect membrane permeability?

Accepted Answer

Double bonds create kinks, preventing close packing and increasing membrane permeability.

Question 5

A cell is placed in a solution and begins to swell. Which of the following best describes the tonicity of the solution relative to the cell?

Accepted Answer

The solution is hypotonic to the cell.

Question 6

Which of the following statements about osmosis is correct?

Accepted Answer

Osmosis is the diffusion of water across a selectively permeable membrane.

Question 7

If the temperature of a membrane decreases, what is the most likely effect on membrane fluidity and permeability?

Accepted Answer

Fluidity and permeability both decrease.

Question 8

Which of the following best explains why cholesterol is important in animal cell membranes at physiological temperatures?

Accepted Answer

Cholesterol restrains phospholipid movement, making the membrane less fluid.

Question 9

Which of the following is a function of membrane proteins?

Accepted Answer

They can facilitate the transport of specific molecules across the membrane.

Question 10

A researcher observes that a certain ion moves across a membrane only when a specific protein is present, and the movement is down its concentration gradient. What type of transport is this?

Accepted Answer

Facilitated diffusion

Question 11

Which of the following best describes the movement of $Na^+$ and $K^+$ ions by the sodium-potassium pump?

Accepted Answer

$Na^+$ is pumped out and $K^+$ is pumped in, both against their concentration gradients using ATP.

Question 12

Which of the following would most likely increase the permeability of a cell membrane to water?

Accepted Answer

Increasing the number of aquaporin proteins in the membrane.

Question 13

A vesicle containing a 0.5 M solution of glucose is placed in a beaker containing a 1.0 M solution of glucose. What will happen to the vesicle?

Accepted Answer

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

Question 14

Which of the following factors would decrease the fluidity of a cell membrane?

Accepted Answer

Increasing the length of phospholipid tails.

Question 15

Which of the following is true about the selective permeability of phospholipid bilayers?

Accepted Answer

Small non-polar molecules cross quickly, while large polar or charged molecules cross slowly or not at all.

Question 16

A cell is placed in an isotonic solution. What will happen to the net movement of water?

Accepted Answer

There will be no net movement of water.

Question 17

Which of the following best describes facilitated diffusion?

Accepted Answer

Movement of molecules down their concentration gradient through a membrane protein, without energy input.

Question 18

Which of the following is NOT a function of the plasma membrane?

Accepted Answer

Synthesizing DNA for cell division.

Question 19

Which of the following statements about membrane proteins is correct?

Accepted Answer

Integral membrane proteins span the membrane and have hydrophobic regions.

Question 20

A cell uses ATP to move $K^+$ ions into the cell and $Na^+$ ions out of the cell, both against their concentration gradients. What type of transport is this?

Accepted Answer

Active transport

Membranes: Structure, Function, and Permeability

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