Question 1

The plasma membrane Na⁺/K⁺-ATPase pump A)is used to generate sodium and potassium gradients across the membrane. B)is a symporter. C)is a pump for active transport of K⁺ out of the cell and Na⁺ into the cell. D)is a pump for facilitated diffusion of K⁺ into the cell and Na⁺ out of the cell. E)does not require ATP.

Accepted Answer

The plasma membrane Na⁺/K⁺-ATPase pump is used to generate sodium and potassium gradients across the membrane through active transport, which requires the input of ATP.

Question 2

The movement of sucrose and H⁺ into the cell by the same membrane protein reflects the actions of what type of transporter? A)Voltage-gated channel. B)Mechanosensitive channel. C)Uniporter. D)Symporter. E)Antiporter.

Accepted Answer

The movement of both sucrose and H⁺ into the cell by the same membrane protein indicates that they are likely being transported together as a single unit, which suggests a symporter type of transporter. Uniporters transport only one type of molecule or ion, while antiporters transport two types of molecules or ions in opposite directions. Voltage-gated channels are gated based on changes in membrane potential, while mechanosensitive channels respond to mechanical stimuli such as pressure or tension.

Question 3

What process best characterizes Ca²⁺ movement from the cytosol (low Ca²⁺ concentration)into the endoplasmic reticulum (high Ca²⁺ concentration)? A)Calcium movement is spontaneous. B)Calcium movement involves active transport. C)Calcium movement occurs by facilitated diffusion using a transporter protein. D)Calcium movement does not require energy. E)Calcium movement occurs by passive diffusion.

Accepted Answer

Moving calcium ions (Ca2+) from a region of low concentration in the cytosol to a region of high concentration in the endoplasmic reticulum requires energy, which is characteristic of active transport mechanisms.

Question 4

________ bind two or more ions or molecules and transport them in opposite directions across a membrane.
A)Uniporters
B)Symporters
C)Antiporters
D)Dual transporters
E)Channel pumps

Accepted Answer

Antiporters bind two or more ions or molecules and transport them in opposite directions across a membrane. Uniporters transport only one ion or molecule, symporters transport two or more ions or molecules in the same direction, dual transporters can transport two or more ions or molecules in either the same or opposite direction, and channel pumps are not a recognized classification of transporters.

Question 5

The best way to describe cellular membranes are
A)fluid with lipid rafts.
B)solely composed of lipids.
C)composed of a single layer of amphipathic molecules.
D)selective to the transport of gases and small molecules only.
E)found in eukaryotes,but not prokaryotes.

Accepted Answer

Cellular membranes are composed mainly of lipids, but they are not solely composed of lipids. They are also fluid and contain lipid rafts, which are areas of the membrane that are denser in cholesterol and saturated fats and play a role in membrane organization and signaling.

Answer: E 
 Cellular membranes are found in both eukaryotes and prokaryotes.

Question 6

Following a meal,glucose must move from the gut lumen where there is a high glucose concentration into the intestinal cell where there is a relatively low level of glucose.This movement is called
A)passive diffusion.
B)facilitated diffusion.
C)active transport.
D)endocytosis.
E)exocytosis.

Accepted Answer

Glucose moves from an area of high concentration to an area of low concentration with the help of a carrier protein. This process is called facilitated diffusion.

Question 7

How might a plant cell compensate for the excessive membrane fluidity that occurs during prolonged exposures to elevated temperature?
A)Reduce membrane cholesterol content.
B)Alter the lipid composition to have longer fatty acyl tails and fewer double bonds.
C)Alter the lipid composition to have shorter fatty acyl tails and more double bonds.
D)Alter the lipid composition to have shorter and more unsaturated fatty acyl tails.
E)Reduce cholesterol content and alter the lipid composition to have shorter fatty acyl tails.

Accepted Answer

To compensate for excessive membrane fluidity at elevated temperatures, a plant cell can alter its lipid composition to have longer fatty acyl tails and fewer double bonds. Longer tails and saturation (lack of double bonds) increase the interaction between the fatty acids, thus reducing fluidity and stabilizing the membrane structure.

Question 8

The pressure required to stop water from moving across the membrane by osmosis is called
A)transport pressure.
B)crenation pressure.
C)atmospheric pressure.
D)osmotic pressure.
E)mechanical pressurE.

Accepted Answer

The pressure required to stop water from moving across the membrane by osmosis is called osmotic pressure. This pressure is generated by the solutes present in the solution on one side of the membrane, which draws water molecules across the membrane to equalize the concentration of solutes on both sides. The higher the concentration of solutes, the higher the osmotic pressure required to stop water flow.

Question 9

Cellular membranes are mosaic and
A)fluid.
B)rigid.
C)symmetrical.
D)highly permeable to large molecules.
E)polar.

Accepted Answer

Cellular membranes are constantly in motion and have a fluid nature, allowing for the movement of molecules and proteins within the membrane. This was first proposed by the fluid mosaic model of the cell membrane. Rigid and symmetrical membranes would limit the movement of molecules and proteins. Cellular membranes are selectively permeable and allow small molecules and ions to pass through but are less permeable to large molecules. Membranes are composed of both polar and nonpolar regions.

Question 10

Passive diffusion
A)is the process by which molecules move from an area of low concentration to an area of high concentration.
B)is a spontaneous process.
C)requires the presence of a transmembrane protein.
D)will occur so long as the membrane is freely permeable to the solute.
E)requires energy.

Accepted Answer

The answer of Passive diffusion
A)is the process by which molecules...

Question 11

Scientists unearth a Wooly Mammoth from the Siberian Ice Sheath and discover that a eukaryotic "amoeba"-like cell is still alive.Which component of the cell membrane might contribute to maintaining the fluidity of plasma membranes under freezing conditions?
A)Peripheral proteins
B)High levels of long fatty acyl tails within the lipid bilayer
C)High levels of unsaturated fatty acyl tails within the lipid bilayer
D)Absence of cholesterol
E)High levels of saturated fatty acyl tails within the lipid bilayer

Accepted Answer

High levels of unsaturated fatty acyl tails within the lipid bilayer contribute to maintaining fluidity of plasma membranes under freezing conditions. Unsaturated fatty acids have kinks in their tails due to double bonds, which prevent them from packing tightly together and create more space for movement. This prevents the membrane from becoming too rigid and potentially damaging the cell.

Question 12

What are the two major components of cell membranes?
A)Glycolipids and phospholipids
B)Cholesterol and proteins
C)Phospholipids and carbohydrates
D)Phospholipids and cholesterol
E)Phospholipids and proteins

Accepted Answer

The main components of cell membranes are phospholipids which form the bilayer structure of the membrane and proteins which are embedded within the phospholipid bilayer and perform various functions such as transport, signaling and structural support. While cholesterol is also present in cell membranes, it is not a major component and serves to stabilize the membrane structure. Carbohydrates are also present, but they are found attached to proteins or lipids on the exterior surface of the membrane and serve as recognition sites for cell-cell interactions. Glycolipids are a combination of carbohydrates and lipids, but they are not major components of cell membranes.

Question 13

The release of the protein insulin from pancreatic cells occurs by
A)endocytosis.
B)pinocytosis.
C)phagocytosis.
D)exocytosis.
E)receptor-mediated endocytosis.

Accepted Answer

Insulin is a protein hormone produced by the beta cells of the pancreas. When insulin is needed, it is released into the bloodstream by exocytosis, which is the process of fusing insulin-containing vesicles with the plasma membrane and releasing their contents outside the cell. This allows insulin to be transported to its target tissues, where it can bind to its receptor and signal for glucose uptake. The other options (A, B, C, E) are all types of endocytosis, which is the process of internalizing substances into the cell. This is the opposite of exocytosis and is not involved in insulin release.

Question 14

An artificial membrane vesicle is mixed with several peripheral membrane proteins and analyzed by freeze-fracture electron microscopy.What will be seen in the resulting image?
A)Bumps will be visible on both layers
B)Bumps will be visible only in the extracellular face (E face)
C)Bumps will be visible in the protoplasmic face (P face)
D)No bumps will be visible in either face

Accepted Answer

Peripheral membrane proteins do not integrate into the lipid bilayer; instead, they are loosely attached to the outer or inner surfaces of the membrane. Freeze-fracture electron microscopy primarily reveals structures within the membrane itself, such as transmembrane proteins or the bilayer's organization. Since peripheral proteins are not embedded within the membrane, they would not be visible as bumps in either the protoplasmic (P) or extracellular (E) faces in the freeze-fracture images.

Question 15

Water diffuses through certain organs such as the kidneys and bladder much faster than would occur by passive diffusion through a lipid bilayer alone.What accounts for this more rapid rate of water transport in these organs?
A)The composition of lipids changes to promote water transport.
B)Presence of aquaporin channels for facilitated diffusion of water.
C)Presence of a water pump.
D)Presence of an ATP-driven enzyme for water transport.
E)The presence of molecules that bind water and change its membrane permeability properties.

Accepted Answer

The presence of aquaporin channels allows for facilitated diffusion of water, resulting in a more rapid rate of water transport compared to passive diffusion through a lipid bilayer alone.

Question 16

Cell surface molecules are labeled with a fluorescent tag and then a portion of them are bleached with a laser beam.What would one observe after the cell is incubated for a few minutes?
A)The bleached molecules would disappear into the cell.
B)The bleached molecules would diffuse laterally through the membrane and intermix with unbleached molecules.
C)The bleached molecules would remain in the spot where bleaching occurred.
D)All the bleached molecules would flip-flop across the cell membrane.
E)The bleached molecules would be released from the cell.

Accepted Answer

After bleaching a portion of the cell surface molecules, the bleached molecules would diffuse laterally through the membrane and intermix with unbleached molecules over time. This process is known as fluorescence recovery after photobleaching (FRAP) and is commonly used to study the dynamics of cell surface molecules. Option A and Option E are not correct as bleached molecules would not disappear into the cell or be released from the cell. Option C is not correct as the bleached molecules would not remain in the spot where bleaching occurred. Option D is not correct as all the bleached molecules would not flip-flop across the cell membrane.

Question 17

Which membrane component is most important for allowing large,charged molecules to pass through the membrane?
A)Peripheral proteins
B)Cholesterol
C)Glycosylated lipids
D)Transmembrane proteins
E)Carbohydrate channels

Accepted Answer

Transmembrane proteins are the most important for allowing large, charged molecules to pass through the membrane. These proteins have hydrophilic regions that function as channels, allowing the charged molecules to pass through the hydrophobic interior of the membrane.

Question 18

In order to study a cell at lower temperatures,a researcher must artificially increase its membrane fluidity.What would be a reasonable strategy for increasing plasma membrane fluidity at low temperatures?
A)Decrease the composition of cholesterol in the plasma membrane
B)Increase the composition of phospholipids with saturated fatty acid chains
C)Decrease the composition of phospholipids with unsaturated fatty acid chains
D)Decrease the length of the phospholipid fatty acyl tail.
E)All of the above strategies are reasonable

Accepted Answer

Decreasing the length of the phospholipid fatty acyl tails increases membrane fluidity by reducing the van der Waals forces between the tails, making the membrane more fluid at lower temperatures.

Question 19

Acetylcholine binds this membrane protein,which subsequently opens to allow sodium to enter the cell.Acetylcholine exerts its effect on what type of transport protein?
A)Ligand-gated channel
B)Voltage-gated channel
C)Mechanosensitive-gated channels
D)Uniporter
E)Symporter

Accepted Answer

Acetylcholine binds to a specific receptor on a ligand-gated ion channel, causing it to open and allowing sodium ions to enter the cell. This is a common mechanism for many neurotransmitters in the nervous system.

Question 20

Sodium concentrations are higher outside and glucose concentrations are higher inside the cell.Using the same membrane protein for Na⁺ and glucose transport,what is it called when a Na⁺ electrochemical gradient is used to drive glucose transport into the cell against its concentration gradient? A)Primary active transport B)Secondary active transport C)Primary facilitated diffusion D)Secondary facilitated diffusion E)Passive diffusion

Accepted Answer

This is an example of secondary active transport, where the electrochemical gradient of one molecule (sodium) is used to drive the transport of another molecule (glucose) against its concentration gradient. In this case, the membrane protein is acting as a symporter, simultaneously transporting the two molecules in the same direction. Primary active transport would require the direct use of ATP to drive the transport, while facilitated diffusion (whether primary or secondary) does not involve the use of energy to move molecules against their concentration gradient. Passive diffusion refers to the movement of molecules down their concentration gradient without the use of a membrane protein.

Quiz 5: Membrane Structure, Transport, and Cell Junctions

The plasma membrane Na⁺/K⁺-ATPase pump

The movement of sucrose and H⁺ into the cell by the same membrane protein reflects the actions of what type of transporter?

What process best characterizes Ca²⁺ movement from the cytosol (low Ca²⁺ concentration) into the endoplasmic reticulum (high Ca²⁺ concentration) ?

________ bind two or more ions or molecules and transport them in opposite directions across a membrane.

The best way to describe cellular membranes are

Following a meal,glucose must move from the gut lumen where there is a high glucose concentration into the intestinal cell where there is a relatively low level of glucose.This movement is called

How might a plant cell compensate for the excessive membrane fluidity that occurs during prolonged exposures to elevated temperature?

The pressure required to stop water from moving across the membrane by osmosis is called

Cellular membranes are mosaic and

Passive diffusion

Scientists unearth a Wooly Mammoth from the Siberian Ice Sheath and discover that a eukaryotic "amoeba"-like cell is still alive.Which component of the cell membrane might contribute to maintaining the fluidity of plasma membranes under freezing conditions?

What are the two major components of cell membranes?

The release of the protein insulin from pancreatic cells occurs by

An artificial membrane vesicle is mixed with several peripheral membrane proteins and analyzed by freeze-fracture electron microscopy.What will be seen in the resulting image?

Water diffuses through certain organs such as the kidneys and bladder much faster than would occur by passive diffusion through a lipid bilayer alone.What accounts for this more rapid rate of water transport in these organs?

Cell surface molecules are labeled with a fluorescent tag and then a portion of them are bleached with a laser beam.What would one observe after the cell is incubated for a few minutes?

Which membrane component is most important for allowing large,charged molecules to pass through the membrane?

In order to study a cell at lower temperatures,a researcher must artificially increase its membrane fluidity.What would be a reasonable strategy for increasing plasma membrane fluidity at low temperatures?

Acetylcholine binds this membrane protein,which subsequently opens to allow sodium to enter the cell.Acetylcholine exerts its effect on what type of transport protein?

Sodium concentrations are higher outside and glucose concentrations are higher inside the cell.Using the same membrane protein for Na⁺ and glucose transport,what is it called when a Na⁺ electrochemical gradient is used to drive glucose transport into the cell against its concentration gradient?