Q: Which of the following equations correctly represents the electrochemical gradient for an ion across a membrane?

$$\text{Electrochemical gradient} = \text{concentration gradient} + \text{membrane potential}$$

Question 1

Which of the following statements best explains why ions such as Na$$^+$$ and K$$^+$$ cannot freely diffuse across a protein-free artificial lipid bilayer?

Accepted Answer

Ions are charged and the hydrophobic core of the bilayer is impermeable to charged molecules.

Question 2

Refer to the diagram showing the permeability of an artificial lipid bilayer. Which molecule would diffuse most rapidly across a protein-free lipid bilayer?

Accepted Answer

CO$$_2$$

Question 3

A cell is placed in a solution where the extracellular Na$$^+$$ concentration is much higher than the intracellular concentration. What prevents Na$$^+$$ from freely entering the cell?

Accepted Answer

The lipid bilayer is impermeable to inorganic ions without specific transport proteins.

Question 4

Which of the following best describes the difference between a channel and a transporter protein?

Accepted Answer

Channels form hydrophilic pores for passive diffusion, while transporters undergo conformational changes to move specific solutes.

Question 5

Which of the following equations correctly represents the electrochemical gradient for an ion across a membrane?

Accepted Answer

$$	ext{Electrochemical gradient} = 	ext{concentration gradient} + 	ext{membrane potential}$$

Question 6

Which of the following is a real-life example of active transport in animal cells?

Accepted Answer

Na$$^+/K$^+$$ ATPase pumping Na$$^+$$ out and K$$^+ in $$using ATP hydrolysis

Question 7

A mutation disables the Na$$^+/K$^+$$ ATPase in a neuron. What is the most likely immediate effect?

Accepted Answer

The cell will lose its ability to maintain a low intracellular Na$$^+$$ and high K$$^+$$ concentration.

Question 8

Which of the following best explains why K$$^+$$ leak channels are important for the resting membrane potential in animal cells?

Accepted Answer

They allow K$$^+ to $$flow out of the cell, leaving behind unbalanced negative charges.

Question 9

Which of the following is true about the selectivity of ion channels?

Accepted Answer

Ion channels select ions based on size and charge, with a selectivity filter that fits specific ions.

Question 10

A patient is diagnosed with a genetic defect in aquaporin proteins. Which physiological process would be most directly affected?

Accepted Answer

Rapid movement of water across cell membranes

Question 11

Which of the following best describes the mechanism of a symport transporter?

Accepted Answer

It couples the movement of two solutes in the same direction, one down its gradient and one against.

Question 12

Which of the following scenarios best illustrates the concept of an electrochemical gradient driving secondary active transport?

Accepted Answer

Na$$^+$$ flows into a cell down its gradient, providing energy for glucose uptake against its gradient.

Question 13

Which of the following is NOT a feature of ion channel gating?

Accepted Answer

Channels require ATP hydrolysis to open and close.

Question 14

Patch-clamp recording is a technique used to:

Accepted Answer

Measure the electrical current through a single ion channel.

Question 15

Which of the following best explains why K$$^+$$ passes through K$$^+$$ channels 10,000 times more readily than Na$$^+$$?

Accepted Answer

The selectivity filter of the channel precisely fits the dehydrated K$$^+$$ ion, but not Na$$^+.$$

Question 16

Which of the following is a direct consequence of the Na$$^+/K$^+$$ ATPase activity in animal cells?

Accepted Answer

The cytosol maintains a low Na$$^+$$ and high K$$^+$$ concentration compared to the extracellular fluid.

Question 17

Which of the following best describes the role of the Ca$$^{2+}$$ ATPase in muscle cells?

Accepted Answer

It pumps Ca$$^{2+}$$ out of the cytosol into the sarcoplasmic reticulum, allowing muscle relaxation.

Question 18

Which of the following is a unique feature of plant, fungal, and bacterial cells regarding membrane transport?

Accepted Answer

They rely on H$$^+$$ pumps to create electrochemical gradients for active transport.

Membrane Transport Proteins and Ion Channels: Structure, Function, and Genetic Relevance

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