Question 1

Which of the following best describes the difference between direct and indirect active transport as illustrated in the provided images?

Accepted Answer

Direct active transport couples solute movement to an exergonic chemical reaction, typically ATP hydrolysis, while indirect active transport couples solute movement to the movement of another ion down its gradient.

Question 2

The Na+/K+ ATPase is classified as which type of transport ATPase?

Accepted Answer

P-type ATPase

Question 3

In the Na+/K+ pump cycle, which event triggers the transition from the E1 to the E2 conformation?

Accepted Answer

Phosphorylation of the pump after Na+ ions are released to the outside

Question 4

Which of the following statements about the E2 conformation of the Na+/K+ pump is correct?

Accepted Answer

It binds K+ strongly and Na+ weakly.

Question 5

A cell uses a Na+/glucose symporter to import glucose against its concentration gradient. What is the immediate energy source for this transport?

Accepted Answer

The Na+ gradient maintained by the Na+/K+ ATPase

Question 6

Given the equation $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$, what does a positive $$\Delta G_{	ext{inward}}$$ indicate about the direction of solute transport?

Accepted Answer

Transport is endergonic and requires energy input.

Question 7

A bacterium maintains an internal lactose concentration of 10 mM and an external concentration of 0.2 mM. Using $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$, what can be concluded about the energy requirement for lactose uptake?

Accepted Answer

Lactose uptake is endergonic and requires energy input.

Question 8

For charged solutes, the equation $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}} + zFV_m is $$used. What effect does a negative membrane potential ($$V_m) $$have on the inward transport of cations?

Accepted Answer

It makes $$\Delta G$$ more negative, favoring inward transport.

Question 9

In a nerve cell, the inward movement of Cl– ions is down the concentration gradient but up the charge gradient. Using $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}} + zFV_m$$, what is the net effect on $$\Delta G$$ for Cl– import if $$V_m is $$negative?

Accepted Answer

The negative membrane potential increases the energy required for Cl– import.

Question 10

Which of the following best explains why the Na+/K+ pump moves three Na+ ions out for every two K+ ions in?

Accepted Answer

To generate and maintain the membrane potential (Vm) of the cell.

Question 11

Which of the following is a real-world example of indirect active transport in human physiology?

Accepted Answer

The uptake of glucose in intestinal epithelial cells via Na+/glucose symport.

Question 12

If the relative transport rate of amino acids increases with increasing Na+ concentration, as shown in the provided graph, what does this suggest about the mechanism of amino acid uptake?

Accepted Answer

Amino acid uptake is coupled to Na+ transport via a symporter.

Question 13

Which of the following is NOT a function of V-type ATPases?

Accepted Answer

Synthesizing ATP in mitochondria.

Question 14

A cell is importing a positively charged solute (z = +1) with a negative membrane potential ($$V_m = -60 mV). $$Using $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}} + zFV_m$$, what is the effect of the membrane potential on the energetics of transport?

Accepted Answer

It makes the transport more energetically favorable.

Question 15

Which of the following best describes the role of ATP in the Na+/K+ pump mechanism?

Accepted Answer

ATP is hydrolyzed to provide energy for the conformational change that allows Na+ and K+ to be transported against their gradients.

Question 16

Which equation would you use to calculate the free energy change for the inward transport of an uncharged solute?

Accepted Answer

$$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$

Question 17

Which of the following is a plausible consequence if the Na+/K+ ATPase stopped functioning in a neuron?

Accepted Answer

The neuron would lose its membrane potential and be unable to transmit nerve impulses.

Question 18

Which of the following is true regarding the energetics of transport for uncharged solutes?

Accepted Answer

Only the concentration gradient is relevant for calculating $$\Delta G.$$

Question 19

If a cell needs to import a solute against both its concentration and electrical gradient, which type of transport mechanism is most likely required?

Accepted Answer

Direct active transport

Active Transport and Energetics of Membrane Transport in Cells

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