Question 1

Osmosis does not occur if the concentration gradients for water and solutes are absent in a system.

Accepted Answer

Osmosis is the movement of water across a semipermeable membrane from an area of high concentration to an area of low concentration. If there are no concentration gradients for water or solutes, there will be no net movement of water and osmosis will not occur.

Question 2

Placing pure water around cells causes the cells to swell because the cytosol has a lower osmotic pressure than the pure water.

Accepted Answer

The answer of Placing pure water around cells causes the...

Question 3

At resting membrane potential, passive and active forces exactly balance each other so there is no net movement of ions across the membrane.

Accepted Answer

At resting membrane potential, the passive diffusion of ions down their concentration gradient is balanced by the active transport of ions against their concentration gradient, so there is no net movement of ions across the membrane.

Question 4

Dephosphorylation of the Na⁺-K⁺ pump causes three Na+ ions to move out of a cell against a concentration gradient.

Accepted Answer

Dephosphorylation of the Na⁺-K⁺ pump causes two K⁺ ions to move into the cell, not Na⁺ ions to move out. The movement of three Na⁺ ions out of the cell occurs during the phosphorylation step.

Question 5

With secondary active transport, sodium ions move along a concentration gradient but against an electrical gradient.

Accepted Answer

The answer of With secondary active transport, sodium ions move...

Question 6

Most of a membrane potential is established by the passive movement of different cations into and out of a cell.

Accepted Answer

The movement of different cations, such as sodium (Na+), potassium (K+), and chloride (Cl-), across the cell membrane through ion channels and other transporters creates a concentration gradient that contributes to the establishment of a membrane potential. This process is passive and does not require energy input from the cell. However, active transport mechanisms, such as the sodium-potassium pump, also play a role in maintaining the membrane potential by actively moving ions against their concentration gradients.

Question 7

At equilibrium, when no net diffusion of Na⁺ or K⁺ is occurring through the membrane, Na+-K⁺ pumps do not have to pump Na⁺ or K⁺.

Accepted Answer

Even at equilibrium, the Na+-K+ pumps must continue to operate to maintain the concentration gradients of Na+ and K+ across the membrane, as these ions can still leak through the membrane.

Question 8

In cystic fibrosis, defective chloride channels allow too many chloride ions to enter the cell, causing the cell to become hypertonic to the ECF and swell.

Accepted Answer

In cystic fibrosis, defective chloride channels result in a decreased amount of chloride exiting the cell, causing the cell to become hypotonic to the ECF and dehydrated, not hypertonic and swollen.

Question 9

Large protein anions do not leave the cell because there is no concentration or electrical gradient to drive it outward.

Accepted Answer

The answer of Large protein anions do not leave the...

Question 10

According to the Nernst equation, the equilibrium potential for a given ion decreases as the difference in concentration of the ion outside and inside the cell increases.

Accepted Answer

The answer of According to the Nernst equation, the equilibrium...

Question 11

Net sodium movement into the cell occurs passively, whereas net sodium movement out of the cell occurs actively.

Accepted Answer

This statement is true. Net sodium movement into the cell occurs passively due to the concentration gradient, while net sodium movement out of the cell requires energy and occurs actively through the use of the sodium-potassium pump.

Question 12

Under normal conditions, the movement of potassium into a cell always requires the splitting of ATP.

Accepted Answer

The movement of potassium into a cell is an example of active transport, which always requires energy in the form of ATP.

Question 13

At resting membrane potential, sodium and potassium ions are no longer moving across the membrane.

Accepted Answer

At resting membrane potential, there is a continual movement of sodium and potassium ions across the membrane through leak channels. This movement helps establish and maintain the resting membrane potential.

Question 14

At the equilibrium potential for K⁺, the concentration and electrical gradients for K⁺ are in opposition to each other and exactly balance each other so there is no net movement of K⁺.

Accepted Answer

This statement accurately describes the concept of equilibrium potential, which is the point at which there is no net movement of ions across the cell membrane because the electrical and concentration gradients are exactly balanced.

Question 15

Leak channels for sodium are closed during the resting potential but open with appropriate stimulation.

Accepted Answer

The answer of Leak channels for sodium are closed during...

Question 16

Carriers that perform facilitated diffusion or secondary active transport of glucose do not split ATP.

Accepted Answer

Facilitated diffusion and secondary active transport do not require ATP hydrolysis, so carriers that perform these processes do not split ATP.

Question 17

If a cell begins to swell after being placed into a salt solution, the salt solution must have a lower osmotic pressure than the cytosol.

Accepted Answer

The answer of If a cell begins to swell after...

Question 18

A membrane potential of -50 mV is greater than a membrane potential of -70 mV.

Accepted Answer

The answer of A membrane potential of -50 mV is...

Question 19

The SGLT and GLUT carriers do not split ATP.

Accepted Answer

SGLT (sodium glucose cotransporter) and GLUT (glucose transporter) are both facilitative glucose transporters and do not require ATP to transport glucose across the cell membrane. SGLT uses the energy of the electrochemical gradient of sodium ions to transport glucose against its concentration gradient, while GLUT transports glucose down its concentration gradient.

Question 20

Sodium-potassium pumps indirectly provide the energy source for SGLT carriers in intestinal cells.

Accepted Answer

Sodium-potassium pumps actively transport ions against their concentration gradient, creating a gradient of energy that can be used by other transporters such as SGLT carriers to move glucose against its concentration gradient. Therefore, sodium-potassium pumps indirectly provide the energy source for SGLT carriers in intestinal cells.

Quiz 3: The Plasma Membrane and Membrane Potential