QCM : Cell Membrane Transport Mechanisms — 12 questions

Questions et réponses du QCM

1. What is a primary effect of the active transport process carried out by the Na⁺-K⁺ pump in cells?

It maintains ionic gradients essential for nerve and muscle function
It directly causes the diffusion of glucose into the cell
It facilitates passive water movement across the membrane
It prevents the movement of ions through channel proteins

It maintains ionic gradients essential for nerve and muscle function

Explication

The Na⁺-K⁺ pump actively transports Na⁺ out of and K⁺ into the cell, maintaining the ionic gradients necessary for nerve impulses, muscle contractions, and overall cellular homeostasis. This is a direct cause-effect relationship where active transport ensures ionic balance.

2. What is the primary role of simple diffusion in cellular transport?

To require membrane proteins for the transport of large polar molecules
To enable water to pass through aquaporins for passive water movement
To facilitate the passive movement of small, lipid-soluble molecules across the membrane along their concentration gradient
To actively move ions against their concentration gradient using energy

To facilitate the passive movement of small, lipid-soluble molecules across the membrane along their concentration gradient

Explication

Simple diffusion's main function is to allow small, hydrophobic molecules like O₂ and CO₂ to passively cross the lipid bilayer along their concentration gradient, without the need for energy or membrane proteins.

3. What does secondary active transport refer to?

Transport of molecules directly using ATP hydrolysis
Coupled transport of two different solutes where one is driven by the electrochemical gradient of the other
Movement of molecules along their concentration gradient without assistance
Passive movement of ions through channel proteins

Coupled transport of two different solutes where one is driven by the electrochemical gradient of the other

Explication

Secondary active transport involves the coupled movement of two different solutes across the membrane, where the movement of one solute is driven by the electrochemical gradient of another, without direct ATP hydrolysis. This distinguishes it from primary active transport, which directly uses ATP.

4. When was the function of the Na⁺-K⁺ pump, including its ATP consumption of about 25% of cellular ATP, first established in scientific research?

1970s
1950s
1990s
1920s

1950s

Explication

The Na⁺-K⁺ pump's role and its ATP consumption were first elucidated and established in the scientific literature during the 1950s, making this the correct chronological period.

5. What does lipid bilayer permeability refer to?

The property of the membrane that limits the passage of polar molecules and ions, mainly allowing small, hydrophobic molecules to diffuse through
The ability of the membrane to allow all molecules to pass freely without restriction
The capacity of membrane proteins to facilitate the transport of molecules across the membrane
The process by which water moves across the membrane via aquaporins

The property of the membrane that limits the passage of polar molecules and ions, mainly allowing small, hydrophobic molecules to diffuse through

Explication

Lipid bilayer permeability specifically refers to the membrane's property of restricting the passage of polar molecules and ions due to its hydrophobic core, allowing mainly small, hydrophobic molecules to diffuse freely.

6. What is the primary role of cytotic transport in cellular function?

To facilitate the passive movement of molecules through the lipid bilayer without membrane deformation
To allow water to passively diffuse across the membrane via aquaporins
To enable the cell to transport substances in or out by forming vesicles through membrane deformation
To maintain ionic gradients across the membrane through active transport mechanisms

To enable the cell to transport substances in or out by forming vesicles through membrane deformation

Explication

Cytotic transport's main function is to move substances in or out of the cell by deforming the plasma membrane to form vesicles or vacuoles, as seen in endocytosis and exocytosis. This process involves membrane deformation and vesicle formation, enabling cellular intake and secretion of substances, which is distinct from passive permeative processes.

7. How do membrane carrier proteins differ from channel proteins in facilitating diffusion?

Channel proteins actively pump ions against their concentration gradient.
Carrier proteins bind specific molecules and undergo conformational changes to transport them.
Carrier proteins form pores that allow ions to pass through passively.
Channel proteins bind molecules and change shape to transport them.

Carrier proteins bind specific molecules and undergo conformational changes to transport them.

Explication

Carrier proteins differ from channel proteins in that they bind specific molecules and undergo conformational changes to transport these molecules across the membrane, whereas channel proteins form pores that allow ions or molecules to passively diffuse through without changing shape.

8. How can understanding the ATP-driven Na⁺-K⁺ pump be applied in medical treatments?

Utilizing the pump to facilitate water movement across cell membranes
Using the pump to directly generate ATP in mitochondria
Applying the pump's mechanism to enhance passive diffusion of ions
Designing drugs that inhibit the pump to treat hypertension

Designing drugs that inhibit the pump to treat hypertension

Explication

The Na⁺-K⁺ pump is a target for certain drugs, such as cardiac glycosides, which inhibit its activity to increase cardiac contractility. Understanding its mechanism allows for therapeutic manipulation in conditions like heart failure and hypertension. The other options are incorrect because the pump does not generate ATP, does not directly facilitate passive diffusion, nor is it involved in water movement—these are functions of other processes or proteins.

9. What percentage of cellular ATP is consumed by the Na⁺-K⁺ pump?

75%
25%
10%
50%

25%

Explication

The Na⁺-K⁺ pump consumes approximately 25% of the cell's ATP, which is a key fact explicitly stated in the content.

10. Who is credited with the statement that the Na⁺-K⁺ pump consumes approximately 25% of cellular ATP?

Author unknown in the provided content.
Lodish et al.
Hille
Alberts et al.

Author unknown in the provided content.

Explication

The correct answer is 'Author unknown in the provided content' because the source explicitly states the fact about the Na⁺-K⁺ pump's ATP consumption but does not specify an author or a publication name, only referencing it as a key fact in the course outline.

11. What is a key feature of the Na⁺-K⁺ pump function?

It passively allows ions to diffuse across the membrane.
It synthesizes ATP to provide energy for cellular processes.
It actively transports Na⁺ out and K⁺ into the cell against their concentration gradients.
It forms channels that allow ions to flow freely.

It actively transports Na⁺ out and K⁺ into the cell against their concentration gradients.

Explication

The Na⁺-K⁺ pump's key feature is its active transport of sodium out of the cell and potassium into the cell against their concentration gradients, which is essential for maintaining cellular ionic balance and electrical excitability.

12. Who is credited with the discovery of aquaporins, the membrane proteins responsible for water movement across cell membranes?

Albert Einstein
Marie Curie
Peter Agre
Ludwig Boltzmann

Peter Agre

Explication

Peter Agre is credited with discovering aquaporins, the specialized water channel proteins that facilitate passive water movement across cell membranes. The other scientists listed are known for contributions in physics, chemistry, or radioactivity, not membrane water channels.

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Lipid bilayer permeability — limit?

Restricts passage of polar molecules and ions.

Passive transport types — examples?

Simple diffusion, facilitated diffusion, osmosis.

Simple diffusion — mechanism?

Small molecules pass directly through lipid bilayer.

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