Q: Which equation correctly represents the net rate of simple diffusion across a membrane?

$$v_{\text{inward}} = P \Delta [S]$$

Question 1

Which of the following statements best explains why oxygen (O$$_2) $$and carbon dioxide (CO$$_2) $$can readily cross the plasma membrane of erythrocytes by simple diffusion?

Accepted Answer

They are small, nonpolar molecules that can dissolve in the lipid bilayer.

Question 2

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

Accepted Answer

Water will enter the cell, increasing turgor pressure and making the cell firm.

Question 3

Which equation correctly represents the net rate of simple diffusion across a membrane?

Accepted Answer

$$v_{	ext{inward}} = P \Delta [S]$$

Question 4

Which of the following is a key difference between facilitated diffusion and simple diffusion?

Accepted Answer

Facilitated diffusion requires membrane proteins, while simple diffusion does not.

Question 5

A patient with cystic fibrosis has a mutation in the CFTR protein. What is the primary physiological consequence of this mutation?

Accepted Answer

Impaired chloride ion transport leads to thick, dehydrated mucus in the airways.

Question 6

Which of the following best describes the function of aquaporins in cell membranes?

Accepted Answer

They form hydrophilic channels that allow rapid passage of water molecules.

Question 7

Why does the rate of facilitated diffusion reach a maximum at high substrate concentrations?

Accepted Answer

Transport proteins become saturated and cannot increase the rate further.

Question 8

Which of the following transport mechanisms is illustrated by the reciprocal exchange of Cl$$^-$$ and HCO$$_3^-$$ ions in erythrocytes?

Accepted Answer

Antiport facilitated diffusion

Question 9

A cell without a cell wall is placed in a hypertonic solution. What is the most likely cellular response?

Accepted Answer

The cell will shrink as water leaves the cell.

Question 10

Which of the following statements about porins is correct?

Accepted Answer

Porins form large, less specific channels in the outer membranes of bacteria, mitochondria, and chloroplasts.

Question 11

Which of the following best describes the alternating conformation model of carrier proteins?

Accepted Answer

Carrier proteins switch between two conformations, exposing the solute-binding site to opposite sides of the membrane.

Question 12

Which of the following is NOT a property of simple diffusion?

Accepted Answer

Saturable kinetics

Question 13

Which of the following is a real-life example of facilitated diffusion?

Accepted Answer

Glucose uptake into erythrocytes via GLUT1 transporter

Question 14

Which of the following factors does NOT directly affect the permeability coefficient ($$P) in $$the rate equation for simple diffusion?

Accepted Answer

The concentration gradient of the solute

Question 15

Which of the following is true about the movement of ions across membranes?

Accepted Answer

It is determined by both the concentration gradient and the charge gradient (electrochemical potential).

Question 16

Which of the following is a function of ion channels in nerve cells?

Accepted Answer

Facilitating electrical signaling by allowing rapid passage of specific ions

Question 17

Which of the following best describes symport transport?

Accepted Answer

Two solutes are transported in the same direction across the membrane.

Question 18

Which of the following processes is responsible for the movement of water from chamber B to chamber A in the osmosis diagram?

Accepted Answer

Osmosis, due to higher solute concentration in chamber A

Question 19

Which of the following is a property shared by both facilitated diffusion and active transport, but not by simple diffusion?

Accepted Answer

Requirement for membrane proteins

Question 20

Which of the following would most likely occur if a cell with a defective GLUT1 transporter was exposed to high extracellular glucose?

Accepted Answer

Glucose uptake into the cell would be severely reduced, leading to low intracellular glucose.

Transport Across Membranes: Overcoming the Permeability Barrier

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