97. Which of the following statements are correct?
A. Lipid bilayer lacking proteins is highly impermeable to all the charged molecules.
B. Channels have specific binding pockets for the solute molecules they allow to pass.
C. Transporters allow solutes to cross a membrane at much slower rates than do channels.
D. The plasma membrane of many animal cells contains open 𝐾
+ channels, yet the 𝐾
+
concentration in the cytosol is much higher than outside the cell.
E. The membrane potential of an axon temporarily becomes more negative when an action
potential excites it.
A. A, C, D
B. A, C, E
C. A, B, E
D. B, D, E

Detailed Explanation:

The movement of molecules across biological membranes is a complex process that plays a critical role in maintaining cellular function. Membrane transport involves various mechanisms such as passive diffusion, facilitated diffusion, and active transport. Here, we’ll assess the key statements related to membrane transport and determine which ones are correct.

A. Lipid Bilayer Lacking Proteins is Highly Impermeable to All Charged Molecules

This statement is correct. The lipid bilayer of cell membranes is composed primarily of phospholipids, which are hydrophobic. This hydrophobic nature makes the lipid bilayer impermeable to charged molecules, which are hydrophilic. Without proteins (such as transporters or channels) embedded in the membrane, charged molecules cannot pass through the lipid bilayer efficiently.

B. Channels Have Specific Binding Pockets for the Solute Molecules They Allow to Pass

This statement is incorrect. Channels typically form pores or passages that allow specific ions or molecules to move across the membrane based on size and charge. Unlike transporters, which actively bind to the solute and undergo conformational changes, channels do not have specific binding pockets for solute molecules. Instead, they provide a passage for the solute to diffuse through.

C. Transporters Allow Solutes to Cross a Membrane at Much Slower Rates than Do Channels

This statement is correct. Transporters facilitate the movement of solutes across membranes through conformational changes, which occur at a slower rate compared to channels. Channels allow rapid movement of ions or molecules across the membrane, while transporters function more slowly, often requiring energy (ATP) for active transport.

D. The Plasma Membrane of Many Animal Cells Contains Open K+ Channels, Yet the K+ Concentration in the Cytosol is Much Higher Than Outside the Cell

This statement is correct. Potassium (K⁺) channels in the plasma membrane are indeed open in many animal cells, allowing the movement of K⁺ ions. However, the concentration of K⁺ ions is much higher inside the cell compared to the outside. This gradient is maintained by the sodium-potassium pump (Na⁺/K⁺ ATPase), which actively transports K⁺ into the cell while pumping Na⁺ out.

E. The Membrane Potential of an Axon Temporarily Becomes More Negative When an Action Potential Excites It

This statement is incorrect. When an action potential excites an axon, the membrane potential temporarily becomes more positive (depolarization) due to the influx of Na⁺ ions into the cell. Afterward, the membrane repolarizes (becomes more negative) as K⁺ ions exit the cell. The temporary more negative state occurs during repolarization, not depolarization.

Conclusion:

After evaluating the statements, we can conclude that the correct answers are:

• A. Lipid bilayer lacking proteins is highly impermeable to all charged molecules.

• C. Transporters allow solutes to cross a membrane at much slower rates than do channels.

• D. The plasma membrane of many animal cells contains open K⁺ channels, yet the K⁺ concentration in the cytosol is much higher than outside the cell.

Thus, the correct answer is:

A. A, C, D

Final Answer:

A. A, C, D