$$\text{Water diffuses from a region of low } [\text{solute}] \text{ to a region of high } [\text{solute}]$$

$$\text{K}^+ \, \text{in} \rightarrow \text{Na}^+ \, \text{out}$$

Question 1

Which of the following best describes the fluid mosaic model of the plasma membrane?

Accepted Answer

A mosaic of protein molecules bobbing in a fluid bilayer of phospholipids

Question 2

Which type of lipid tail increases membrane fluidity, and why?

Accepted Answer

Unsaturated fatty acid tails, because kinks prevent tight packing

Question 3

A cell is placed in a solution and swells until the cell wall opposes further uptake. What type of solution is the cell in?

Accepted Answer

Hypotonic solution

Question 4

Which of the following statements about membrane proteins is correct?

Accepted Answer

Integral proteins span the membrane and have both hydrophobic and hydrophilic regions

Question 5

What is the main function of transport proteins in the plasma membrane?

Accepted Answer

To allow passage of hydrophilic substances across the membrane, specific for the substance it moves

Question 6

Which equation best represents the movement of water during osmosis across a selectively permeable membrane?

Accepted Answer

$$	ext{Water diffuses from a region of low } [	ext{solute}] 	ext{ to a region of high } [	ext{solute}]$$

Question 7

A red blood cell placed in a hypertonic solution will:

Accepted Answer

Lose water and shrivel

Question 8

Facilitated diffusion differs from simple diffusion in that:

Accepted Answer

Facilitated diffusion uses transport proteins to move molecules down their concentration gradient

Question 9

Which of the following is true about active transport?

Accepted Answer

It moves substances against their concentration gradient and requires energy, usually in the form of ATP

Question 10

The sodium-potassium pump in animal cells exchanges which ions across the plasma membrane?

Accepted Answer

$$	ext{K}^+ \, 	ext{in} ightarrow 	ext{Na}^+ \, 	ext{out}$$

Question 11

Which of the following best explains why cholesterol affects membrane fluidity?

Accepted Answer

Increasing cholesterol within membranes stiffens the membrane, making it less fluid

Question 12

Which process allows large molecules, such as polysaccharides and proteins, to cross the plasma membrane?

Accepted Answer

Bulk transport via vesicles (exocytosis or endocytosis)

Question 13

A plant cell in a hypertonic environment will:

Accepted Answer

Lose water and undergo plasmolysis

Question 14

Which of the following is a function of membrane carbohydrates in cell-cell recognition?

Accepted Answer

They allow cells to recognize each other by binding to surface molecules on the extracellular surface

Question 15

Which of the following molecules can most easily cross the plasma membrane without assistance?

Accepted Answer

Small, nonpolar molecules such as $$	ext{O}_2$$ and $$	ext{CO}_2$$

Question 16

Which of the following best describes the role of aquaporins in the plasma membrane?

Accepted Answer

They provide corridors that allow specific molecules or ions to cross the membrane

Question 17

Which equation best represents the effect of membrane potential on ion movement?

Accepted Answer

$$	ext{Voltage is created by differences in the distribution of anions and cations across a membrane}$$

Question 18

Which of the following is an example of coupled transport by a membrane protein?

Accepted Answer

The transport of sucrose against its concentration gradient with movement of $$	ext{H}^+$$ down its gradient

Question 19

Which of the following is true about ligand-gated ion channels in the plasma membrane?

Accepted Answer

They allow ions to pass only when a signal molecule binds and changes the channel’s shape

Cell Membranes: Structure, Function, and Transport Mechanisms

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