Question 1

The sodium-potassium pump is called an electrogenic pump because it

Accepted Answer

The sodium-potassium pump contributes to the membrane potential by actively transporting 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, creating an electrochemical gradient. This makes it an electrogenic pump.

Answer: A, D, and E are incorrect

A) The pump does not pump equal quantities of Na⁺ and K⁺, but rather pumps out 3 Na⁺ ions for every 2 K⁺ ions it pumps in.
B) The pump does not pump out hydrogen ions.
D) The pump does not ionize sodium and potassium atoms.
E) The pump is not used to drive the transport of other molecules against a concentration gradient, but rather maintains the concentration gradients of Na⁺ and K⁺ by using ATP.

Question 2

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are

Accepted Answer

The cells of the celery stalks are hypertonic to fresh water, causing water to enter the cells and make them stiff. In the salt solution, the cells are hypotonic, causing water to leave the cells and making them limp.

Question 3

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?

Accepted Answer

Facilitated diffusion is the most probable mechanism because it allows for the rapid movement of glucose across cell membranes through specific transport proteins, bypassing the slow diffusion through the phospholipid bilayer.

Question 4

Nitrous oxide gas molecules diffusing across a cell's plasma membrane is an example of

Accepted Answer

Nitrous oxide gas molecules are small, uncharged particles that can passively diffuse across the plasma membrane through the hydrophobic lipid bilayer, which constitutes the majority of the membrane's structure. This process is known as simple diffusion or passive transport, and does not require the input of energy or the presence of specific transport proteins (as in facilitated diffusion or active transport). Osmosis refers specifically to the diffusion of water molecules across a selectively permeable membrane, while cotransport involves the coordinated movement of two or more substances across a membrane.

Question 5

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?

Accepted Answer

CO₂ is a small, nonpolar molecule that can easily move through the hydrophobic interior of the lipid bilayer without much resistance. As such, it would likely move through the membrane most rapidly compared to the other choices, which are either larger or polar.

Question 6

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

Accepted Answer

Carrier proteins exhibit specificity for a particular type of molecule, allowing them to selectively transport molecules across the plasma membrane.

Question 7

When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur?

Accepted Answer

When a plant cell is submerged in a hypotonic solution (lower concentration of solutes), water will move into the cell by osmosis, causing the cell to expand and become turgid. This is because the plant cell has a cell wall that prevents it from bursting or lysing, unlike animal cells. Plasmolysis occurs when a plant cell is in a hypertonic solution (higher concentration of solutes), causing the cell to lose water and shrink. Flaccid occurs when a plant cell is in an isotonic solution (equal concentration of solutes), causing no net movement of water in or out of the cell.

Question 8

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of

Accepted Answer

The answer of The phosphate transport system in bacteria imports...

Question 9

Why are lipids and proteins free to move laterally in membranes?

Accepted Answer

The interior of the membrane is largely composed of hydrophobic tails of the phospholipids. This results in weak hydrophobic interactions which allow for free lateral movement of lipids and proteins. The hydrophilic heads of the phospholipids face the aqueous environment both inside and outside of the cell membrane.

Question 10

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

Accepted Answer

In normal tonicity conditions, animal cells are in an isotonic solution, meaning that the concentration of solutes inside the cell is equal to the concentration of solutes outside of the cell. Plant cells are in a hypotonic solution, meaning that the concentration of solutes outside of the cell is lower than the concentration inside of the cell. This helps maintain the turgor pressure and shape of the plant cell. Therefore, option D is the correct choice.

Question 11

In which of the following would there be the greatest need for osmoregulation?

Accepted Answer

Tidepool animals such as anemones live in an environment with rapidly changing salt concentrations due to tidal cycles. Therefore, they would need to regulate their water and salt balance through osmoregulation.

Question 12

Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?

Accepted Answer

The concentration of NaCl in seawater is much higher than in mammalian blood. Therefore, when red blood cells are transferred to seawater, water will leave the cells due to osmosis, causing them to shrivel and collapse.

Question 13

In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by

Accepted Answer

Cotransport proteins can use the energy stored in the electrochemical gradient of one ion to drive the transport of another ion/molecule against its concentration gradient. This mechanism can account for the gradient of other ions without the need for additional electrogenic pumps.

Question 14

Which of the following statements is correct about diffusion?

Accepted Answer

Diffusion is a passive process in which molecules move from a region of higher concentration to a region of lower concentration, without the need for energy expenditure by the cell. Option A is incorrect because diffusion occurs over short distances. Option B is incorrect because diffusion is a passive process that does not require energy expenditure. Option D is incorrect because it describes active transport, which is the movement of molecules against their concentration gradient and requires energy expenditure. Option E is incorrect because integral proteins are only required for facilitated diffusion, which is a specific type of passive transport.

Question 15

Which of the following is true of the evolution of cell membranes?

Accepted Answer

All components of cell membranes, including lipids and proteins, are subject to natural selection and can evolve over time. This is because cell membranes play crucial roles in determining what goes in and out of cells, as well as cell signaling and communication. Therefore, changes in membrane components can have significant impacts on an organism's survival and reproductive success.

Question 16

Water passes quickly through cell membranes because

Accepted Answer

Water passes quickly through cell membranes via aquaporins, which are specialized channels that allow for facilitated diffusion of water molecules.

Question 17

Cell membranes are asymmetrical. Which of the following is the most likely explanation?

Accepted Answer

The asymmetry of cell membranes is due to the different environments and functions of the two sides of the membrane. For example, the cytoplasmic side of the membrane interacts with the cytoskeleton and regulates intracellular signaling, while the extracellular side interacts with the extracellular matrix and mediates cell-cell communication.

Question 18

What kinds of molecules pass through a cell membrane most easily?

Accepted Answer

Small and hydrophobic molecules pass through a cell membrane most easily because they can dissolve in the phospholipid bilayer of the membrane, which is also hydrophobic. This allows them to move across the membrane without the need for assistance from transport proteins or other mechanisms. Large polar molecules, ionic molecules, and monosaccharides such as glucose cannot pass through the membrane as easily because they cannot dissolve in the hydrophobic interior of the membrane.

Question 19

What is the voltage across a membrane called?

Accepted Answer

The voltage across a membrane is called the membrane potential. This is the difference in electric potential between the interior and exterior of a cell membrane, which is caused by the distribution of ions across the membrane.

Answer: E
 The membrane potential is part of the electrochemical gradient, which refers to the combined effect of the membrane potential and the concentration gradient of ions across the membrane. The electrochemical gradient influences the movement of ions and other molecules across the membrane.

Question 20

Which of the following membrane activities require energy from ATP hydrolysis?

Accepted Answer

Moving the Na⁺ ions against their concentration gradient requires energy in the form of ATP hydrolysis. A is incorrect because facilitated diffusion does not require energy from ATP hydrolysis. B is incorrect because movement of water into a cell by osmosis does not require energy. D is incorrect because movement of glucose down its concentration gradient does not require energy from ATP hydrolysis. E is incorrect because movement of carbon dioxide across the membrane occurs by simple diffusion and does not require energy from ATP hydrolysis.

Quiz 7: Membrane Structure and Function