Question 1

Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

Accepted Answer

The answer of Which of the following is most likely...

Question 2

Water passes quickly through cell membranes because

Accepted Answer

Water passes quickly through cell membranes because it moves through aquaporins in the membrane, which are specific protein channels that allow the facilitated diffusion of water molecules. The aquaporin pores are too narrow for larger polar molecules to pass through, which is why water can move quickly and selectively through these channels.

Question 3

Which of the following statements is correct about diffusion?

Accepted Answer

Diffusion is a passive process in which particles move from an area of higher concentration to an area of lower concentration. It does not require the cell to expend energy. Option A is incorrect because while diffusion is rapid over short distances, it becomes slower as the distance increases. Option B is incorrect because diffusion is passive and does not require energy. Option D is incorrect because it describes active transport, not diffusion. Option E is incorrect because not all types of diffusion require integral proteins in the cell membrane.

Question 4

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 5

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 three sodium ions out of the cell for every two potassium ions pumped into the cell. This creates an electrochemical gradient across the membrane, which helps to maintain the resting potential of the cell.

Question 6

What is the voltage across a membrane called?

Accepted Answer

The voltage across a membrane is called the membrane potential. This refers to the difference in electric potential between the inside and outside of cells, which is created by the uneven distribution of ions across the cell membrane.

Question 7

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 8

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 is higher outside of the red blood cells in seawater compared to inside the cells. This creates a hypertonic environment for the red blood cells, which leads to water leaving the cells through osmosis. This will cause the cells to shrink and collapse, leading to cell death.

Question 9

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 transport two different molecules across the membrane at the same time. One molecule moves down its concentration gradient, which provides the energy to transport the other molecule against its concentration gradient. Therefore, the gradient of one ion can be used to transport another ion against its own gradient, generating an electrochemical gradient for that ion. This process is known as secondary active transport, and it relies on the presence of cotransport proteins to account for the gradients of many ions across the plasma membrane.

Question 10

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, meaning that they only bind to and transport specific substances across the membrane.

Question 11

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

Accepted Answer

CO₂ is a nonpolar molecule and is able to dissolve in the lipid bilayer, moving through it quickly. The other molecules listed are polar and therefore have a harder time passing through the hydrophobic interior of the lipid bilayer.

Question 12

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

Accepted Answer

Tidepool animals such as anemones are exposed to a constantly changing environment of salt and water concentrations. Therefore, they require osmoregulation to maintain proper balance of salt and water in their cells.

Question 13

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 placed in a hypotonic solution, water moves into the cell due to the concentration gradient. This causes the vacuole to expand and put pressure on the cell wall, resulting in the cell becoming turgid. However, if the solution is too hypotonic, the cell may burst.

Question 14

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 answer of Celery stalks that are immersed in fresh...

Question 15

The movement of potassium into an animal cell requires

Accepted Answer

The movement of a substance from an area of low concentration to an area of high concentration (against the concentration gradient) requires an energy source such as ATP. In this case, potassium is moving into the cell against its concentration gradient, so an energy source is necessary.

Question 16

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

Accepted Answer

Typically, animal cells are in isotonic solutions where the concentration of solutes outside and inside the cell is the same. Plant cells, on the other hand, are in hypotonic solutions where the concentration of solutes outside the cell is lower than inside the cell. This is due to the presence of a cell wall that prevents the plant cell from bursting. Therefore, the correct statement is that the animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution, which is described in choice D.

Question 17

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

Accepted Answer

Small and hydrophobic molecules can pass through the cell membrane most easily because they can dissolve in the lipid bilayer. Large polar molecules and ions have a difficult time passing through the hydrophobic interior of the membrane, while monosaccharides require transport proteins to facilitate their passage.

Question 18

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

Accepted Answer

The interior of the membrane is hydrophobic, which means there are only weak hydrophobic interactions that allow lipids and proteins to move laterally in the membrane. This movement is essential for membrane function, such as the movement of proteins to interact with other molecules or to form signaling complexes. The other options are incorrect because the presence of water, repulsion between lipids and proteins, the positioning of hydrophilic portions, and the actions of other molecules do not explain the lateral movement of lipids and proteins in membranes.

Question 19

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

Accepted Answer

Na⁺ ions moving out of a mammalian cell bathed in physiological saline requires energy from ATP hydrolysis because it is moving against its concentration gradient. This is an example of active transport, which requires energy input. The other activities listed do not require ATP hydrolysis, as they either involve movement down a concentration gradient (A, D) or movement of a small, uncharged molecule (B, E).

Question 20

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

Accepted Answer

Nitrous oxide gas is a small, nonpolar molecule that is able to diffuse freely across the lipid bilayer of a cell's plasma membrane without the need for a transport protein or energy input. This process is known as simple diffusion, which is a type of passive transport.

Quiz 7: Membrane Structure and Function