Question 1

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

Accepted Answer

Small hydrophobic molecules, such as oxygen and carbon dioxide, easily pass through cell membranes because they can dissolve in the phospholipid bilayer. Large hydrophobic molecules would not be as easily accommodated in the membrane. Large polar and hydrophilic molecules have trouble passing through the nonpolar phospholipid bilayer. Small ionic molecules would need help from transporter proteins to pass through the membrane. Large and hydrophilic molecules like proteins are too large to pass through the membrane without the help of transport proteins.

Question 2

Which of the following evolutionary adaptations would you expect to find in the cell membranes of Antarctic icefish?

Accepted Answer

Antarctic icefish live in extremely cold water and need a mechanism to prevent their cell membranes from becoming too rigid. Therefore, they have evolved to have a high percentage of unsaturated fatty acids in their cell membranes, which keeps them more fluid at low temperatures.

Question 3

The movement of the hydrophobic gas nitrous oxide (N₂O)(laughing gas)into a cell is an example of

Accepted Answer

Nitrous oxide is a small, hydrophobic molecule that can diffuse through the lipid bilayer of the cell membrane. This is an example of simple diffusion, where molecules move from an area of high concentration to an area of low concentration without the need for energy or a transport protein.

Question 4

The protein,lipid,and carbohydrate compositions of the cytoplasmic and extracellular sides of membranes are different from one another.Why is this the case?

Accepted Answer

The two sides of the cell membrane face different environments and have different functions, so they require different compositions to carry out those functions effectively. For example, the extracellular side of the membrane often contains glycoproteins and glycolipids for cell recognition and signaling, while the cytoplasmic side may have protein transporters and enzymes for cellular metabolism. This asymmetry is essential for proper membrane function.

Question 5

Which of the following is true of integral membrane proteins?

Accepted Answer

Integral membrane proteins are usually transmembrane proteins, which means they span the entire thickness of the membrane bilayer. They are embedded within the hydrophobic interior of the lipid bilayer and often have functional roles such as transport, enzyme activity, or cell signaling. They are not loosely bound to the surface of the bilayer and can be mobile within the bilayer.

Question 6

Which of the following molecules are localized on the exterior of a phospholipid bilayer?

Accepted Answer

Phosphate groups are polar and therefore hydrophilic, making them localized on the exterior of the phospholipid bilayer. Saturated and unsaturated fatty acids are nonpolar and therefore hydrophobic, making them located in the interior of the bilayer. Cholesterol is also located within the bilayer, contributing to its fluidity and stability.

Question 7

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

Accepted Answer

Weak hydrophobic interactions in the interior of the membrane are easily disrupted, allowing for lipids and proteins to move laterally within the membrane. This enables the membrane to be fluid and dynamic, facilitating various cellular processes. The other options are not correct because liquid water would hinder lateral movement, lipids and proteins do not repulse each other in the membrane, and hydrogen bonds with water primarily affect lipid behavior at the membrane surface.

Question 8

A protein that spans the phospholipid bilayer one or more times is

Accepted Answer

A protein that spans the phospholipid bilayer one or more times is called a transmembrane protein. Therefore, choice A is the correct answer. Glycoproteins have carbohydrate chains attached to them, peripheral proteins are attached to the surface of the membrane, and extracellular matrix proteins are located outside the cell membrane.

Question 9

When biological membranes are frozen and then fractured,they tend to break along the middle of the bilayer.The best explanation for this is that

Accepted Answer

The hydrophobic interactions between the non-polar fatty acid tails of the two phospholipid monolayers are the weakest interactions in the membrane. These interactions are responsible for holding the two layers together and the middle of the bilayer is where these weak interactions occur. Therefore, when biological membranes are frozen and fractured, they tend to break along the middle of the bilayer.

Question 10

The primary structural components of the cell membrane are

Accepted Answer

The primary structural components of the cell membrane are phospholipids and proteins. The phospholipids make up the lipid bilayer of the membrane and the proteins serve a variety of functions such as transport and cell signaling. While cholesterol may play a role in membrane fluidity and glycoproteins may be present on the surface of the membrane, they are not the primary structural components. Cellulose is not a component of the cell membrane as it is a structural component of plant cell walls.

Question 11

Several species of bacteria and archaea live in hot springs and deep sea thermal vents where the water temperature exceeds 90°C (194°F).Which of the following evolutionary adaptations would you expect to find in the cell membranes of these thermophilic organisms?

Accepted Answer

Thermophilic organisms living in hot environments have adapted to their extreme conditions by incorporating more saturated fatty acids into their cell membranes. Saturated fatty acids have straight tails that can pack tightly together, making the membrane more stable and less likely to melt at high temperatures.

Question 12

An integral membrane protein would have to be

Accepted Answer

An integral membrane protein must cross the hydrophobic interior of the lipid bilayer and therefore must be amphipathic with at least one hydrophobic and one hydrophilic region. This allows it to interact with both the water and lipid portions of the membrane. It may also contain alpha helix structural domains, but this is not a requirement for all integral membrane proteins.

Question 13

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

Accepted Answer

The double bonds in unsaturated fatty acids create kinks in their tails and prevent adjacent lipids from packing tightly together, increasing the fluidity of the membrane. This is not seen in saturated fatty acids that have straight tails, making them pack together more tightly and resulting in a less fluid membrane.

Question 14

Based on the fluid mosaic model of cell membranes,which of the following statements about membrane phospholipids is true?

Accepted Answer

According to the fluid mosaic model, membrane phospholipids are able to move laterally within the plane of the membrane. This lateral movement allows for the membrane to be dynamic and adaptable to changes in the environment. However, phospholipids do not frequently flip-flop between sides of the membrane, as it is energetically unfavorable. The membrane is also not an uninterrupted bilayer, as it contains various membrane proteins integrated into the phospholipid bilayer. Finally, phospholipids do not leave the bilayer and dissolve in the surrounding solution, as they are amphipathic molecules that are oriented with their hydrophilic heads facing outward towards the aqueous solutions and their hydrophobic tails facing inward towards the membrane interior.

Question 15

Cell membranes in plants that thrive in extreme cold are able to remain fluid by

Accepted Answer

Increasing the percentage of unsaturated phospholipids in the membrane allows for more kinks in the fatty acid tails, preventing them from packing tightly and solidifying at low temperatures. This helps to maintain membrane fluidity in extreme cold.

Question 16

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

Accepted Answer

Carrier proteins in a plasma membrane exhibit a specificity for a particular type of molecule, allowing them to selectively transport certain molecules across the membrane. This is a characteristic feature of carrier proteins. The other options listed are not necessarily true for all carrier proteins. Some may be peripheral membrane proteins, may not require cellular energy to function, and may not work against a concentration gradient.

Question 17

The sugars associated with glycoproteins and glycolipids of animal cell membranes

Accepted Answer

The sugars associated with glycoproteins and glycolipids in animal cell membranes act as markers that enable the immune system to distinguish between self and non-self cells, as well as allowing cells to recognize and interact with one another. They do not serve as an energy source or play a role in maintaining or decreasing membrane fluidity temperature.

Question 18

At human body temperature (37°C),cholesterol in membranes functions to

Accepted Answer

Cholesterol molecules at human body temperature prevent phospholipids from moving too much and make membrane less fluid-like. This enhances the strength of the cell's membrane.

Question 19

The fluid mosaic model of membrane structure suggests that membranes

Accepted Answer

The fluid mosaic model of membrane structure is widely accepted and suggests that membranes are composed of a fluid bilayer of phospholipids with proteins embedded in it. This model explains how membranes are dynamic and able to allow molecules to pass through them while still maintaining their structural integrity.

Question 20

Which of the following membrane proteins tend to lack hydrophobic regions on their surfaces?

Accepted Answer

Peripheral membrane proteins are found on the surface of the membrane and interact primarily with the polar head groups of lipids which are hydrophilic. They tend to lack hydrophobic regions on their surfaces. Transmembrane proteins and integral membrane proteins have hydrophobic regions because they span the entire lipid bilayer. Integrins are transmembrane proteins and have hydrophobic regions.

Quiz 5: Membrane Transport and Cell Signaling

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

Which of the following evolutionary adaptations would you expect to find in the cell membranes of Antarctic icefish?

The movement of the hydrophobic gas nitrous oxide (N₂O) (laughing gas) into a cell is an example of

The protein,lipid,and carbohydrate compositions of the cytoplasmic and extracellular sides of membranes are different from one another.Why is this the case?

Which of the following is true of integral membrane proteins?

Which of the following molecules are localized on the exterior of a phospholipid bilayer?

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

A protein that spans the phospholipid bilayer one or more times is

When biological membranes are frozen and then fractured,they tend to break along the middle of the bilayer.The best explanation for this is that

The primary structural components of the cell membrane are

Several species of bacteria and archaea live in hot springs and deep sea thermal vents where the water temperature exceeds 90°C (194°F) .Which of the following evolutionary adaptations would you expect to find in the cell membranes of these thermophilic organisms?

An integral membrane protein would have to be

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

Based on the fluid mosaic model of cell membranes,which of the following statements about membrane phospholipids is true?

Cell membranes in plants that thrive in extreme cold are able to remain fluid by

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

The sugars associated with glycoproteins and glycolipids of animal cell membranes

At human body temperature (37°C) ,cholesterol in membranes functions to

The fluid mosaic model of membrane structure suggests that membranes

Which of the following membrane proteins tend to lack hydrophobic regions on their surfaces?

Quiz 5: Membrane Transport and Cell Signaling

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

Which of the following evolutionary adaptations would you expect to find in the cell membranes of Antarctic icefish?

The movement of the hydrophobic gas nitrous oxide (N2O) (laughing gas) into a cell is an example of

The protein,lipid,and carbohydrate compositions of the cytoplasmic and extracellular sides of membranes are different from one another.Why is this the case?

Which of the following is true of integral membrane proteins?

Which of the following molecules are localized on the exterior of a phospholipid bilayer?

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

A protein that spans the phospholipid bilayer one or more times is

When biological membranes are frozen and then fractured,they tend to break along the middle of the bilayer.The best explanation for this is that

The primary structural components of the cell membrane are

Several species of bacteria and archaea live in hot springs and deep sea thermal vents where the water temperature exceeds 90°C (194°F) .Which of the following evolutionary adaptations would you expect to find in the cell membranes of these thermophilic organisms?

An integral membrane protein would have to be

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

Based on the fluid mosaic model of cell membranes,which of the following statements about membrane phospholipids is true?

Cell membranes in plants that thrive in extreme cold are able to remain fluid by

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

The sugars associated with glycoproteins and glycolipids of animal cell membranes

At human body temperature (37°C) ,cholesterol in membranes functions to

The fluid mosaic model of membrane structure suggests that membranes

Which of the following membrane proteins tend to lack hydrophobic regions on their surfaces?

The movement of the hydrophobic gas nitrous oxide (N₂O) (laughing gas) into a cell is an example of