Question 1

Which of the following molecules can most easily diffuse across the lipid bilayer of the cell membrane without the aid of a transport protein?

Accepted Answer

O$$_2$$

Question 2

A red blood cell is placed in a hypertonic solution. According to the golden rule of osmosis, what will happen to the cell?

Accepted Answer

It will shrivel as water moves out of the cell.

Question 3

Which of the following statements best describes facilitated diffusion?

Accepted Answer

It uses carrier or channel proteins to move molecules down their concentration gradient.

Question 4

Which property of aquaporins allows them to selectively permit water molecules but exclude ions?

Accepted Answer

Their internal architecture is so precise that even single mischarged ions cannot pass.

Question 5

A patient is given an intravenous solution that is hypotonic relative to their blood plasma. What is the most likely effect on their red blood cells?

Accepted Answer

Cells will swell and may burst due to water influx.

Question 6

Which of the following best explains why ions such as Na$$^+$$ and K$$^+$$ require channel proteins to cross the cell membrane?

Accepted Answer

Their charge prevents them from passing through the hydrophobic core of the lipid bilayer.

Question 7

Which of the following is a key difference between carrier proteins and channel proteins?

Accepted Answer

Carrier proteins undergo conformational changes for each molecule transported, while channel proteins form open pores.

Question 8

The GLUT family of transporters is responsible for which of the following cellular processes?

Accepted Answer

Facilitated diffusion of glucose down its concentration gradient

Question 9

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

Accepted Answer

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

Question 10

A mutation causes a carrier protein to become locked in the occluded state. What is the most likely consequence?

Accepted Answer

The protein will be unable to transport solutes, blocking their passage.

Question 11

Which of the following best describes the role of the lipid bilayer in membrane permeability?

Accepted Answer

It acts as a highly selective barrier, restricting the passage of most polar and charged molecules.

Question 12

Which scenario best illustrates the concept of tonicity?

Accepted Answer

A cell placed in a solution with equal solute concentration remains unchanged.

Question 13

Which of the following is true about ion channels?

Accepted Answer

They allow rapid, passive movement of specific ions across the membrane.

Question 14

A scientist observes that a certain molecule crosses the cell membrane only when a specific protein is present, and the process does not require energy. Which transport mechanism is most likely involved?

Accepted Answer

Facilitated diffusion

Question 15

Which of the following best explains why water can cross the cell membrane rapidly despite being polar?

Accepted Answer

Specialized channel proteins called aquaporins facilitate water movement.

Question 16

Which of the following is a defining feature of passive transport?

Accepted Answer

It moves molecules down their concentration gradient without energy input.

Question 17

A cell is placed in seawater (a hypertonic solution). Using the concept of osmosis, predict the direction of water movement and the fate of the cell.

Accepted Answer

Water will move out of the cell, causing it to shrivel (crenate).

Question 18

Which of the following best describes the selectivity of channel proteins?

Accepted Answer

They are highly selective, allowing only specific ions or water molecules to pass based on size and charge.

Question 19

Which of the following is NOT a characteristic of simple diffusion across the cell membrane?

Accepted Answer

It requires a transmembrane protein.

Question 20

Which of the following best explains why the rate of transport through channel proteins can exceed that of carrier proteins?

Accepted Answer

Channel proteins do not undergo conformational changes for each molecule transported.

Functions of the Cell Membrane: Transport, Endocytosis, and Exocytosis

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