Question 1

The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is
A)to facilitate diffusion of molecules down their concentration gradients.
B)to actively transport molecules against their concentration gradients.
C)to maintain the integrity of a fluid mosaic membrane.
D)to maintain membrane fluidity at low temperatures.
E)to mediate cell-to-cell recognition.

Accepted Answer

Polysaccharides attached to glycoproteins and glycolipids of animal cell membranes function primarily in cell-to-cell recognition, facilitating interactions and signaling between cells. While membrane fluidity and integrity are important properties of cell membranes, they are not directly dependent on the presence of polysaccharides. Similarly, active transport and diffusion are facilitated by membrane proteins rather than polysaccharides.

Question 2

Which of the following is true of the evolution of cell membranes?
A)Cell membranes have stopped evolving now that they are fluid mosaics.
B)Cell membranes cannot evolve if the membrane proteins do not.
C)The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids.
D)All components of membranes evolve in response to natural selection.
E)An individual organism selects its preferred type of cell membrane for particular functions.

Accepted Answer

All components of membranes, including lipids, proteins, and carbohydrates, can evolve in response to natural selection. This evolution can occur in response to changes in environmental conditions or in response to the need for new cell functions. Therefore, choice D is the correct answer. The other choices are not accurate because cell membranes can still evolve, membrane proteins are not the only driving force behind membrane evolution, and individual organisms do not select their own preferred type of cell membrane.

Question 3

Which of the following types of molecules are the major structural components of the cell membrane?
A)phospholipids and cellulose
B)nucleic acids and proteins
C)phospholipids and proteins
D)proteins and cellulose
E)glycoproteins and cholesterol

Accepted Answer

Phospholipids and proteins are the major structural components of the cell membrane. Phospholipids form the lipid bilayer that makes up the framework of the membrane, while proteins are embedded in the lipid bilayer and perform various functions such as transporting molecules into and out of the cell and providing structural support. While cellulose is a structural molecule in plant cell walls, it is not a major component of the cell membrane. Nucleic acids are genetic material and do not contribute to the cell membrane structure. Glycoproteins and cholesterol are present in the membrane, but are not major structural components.

Question 4

The presence of cholesterol in the plasma membranes of some animals
A)enables the membrane to stay fluid more easily when cell temperature drops.
B)enables the animal to remove hydrogen atoms from saturated phospholipids.
C)enables the animal to add hydrogen atoms to unsaturated phospholipids.
D)makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.
E)makes the animal more susceptible to circulatory disorders.

Accepted Answer

Cholesterol helps maintain the fluidity of the plasma membrane by preventing phospholipids from packing too tightly together in cold temperatures, without compromising its structural integrity.

Question 5

In order for a protein to be an integral membrane protein, it would have to be
A)hydrophilic.
B)hydrophobic.
C)amphipathic, with at least one hydrophobic region.
D)completely covered with phospholipids.
E)exposed on only one surface of the membrane.

Accepted Answer

An integral membrane protein must have at least one hydrophobic region in order to embed itself into the hydrophobic interior of the phospholipid bilayer. Additionally, it must have at least one hydrophilic region in order to interact with the aqueous environment on either side of the membrane. Therefore, an integral membrane protein must be amphipathic, with both hydrophobic and hydrophilic regions.

Question 6

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
A)The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
B)Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in membranes.
C)Unsaturated fatty acids are more polar than saturated fatty acids.
D)The double bonds block interaction among the hydrophilic head groups of the lipids.
E)The double bonds result in shorter fatty acid tails and thinner membranes.

Accepted Answer

The double bonds in unsaturated fatty acids create kinks in the fatty acid tails, preventing them from packing tightly and increasing the fluidity of the membrane at lower temperatures.

Question 7

Cell membranes are asymmetrical. Which of the following is the most likely explanation?
A)The cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium.
B)Cell membranes communicate signals from one organism to another.
C)The two sides of a cell membrane face different environments and carry out different functions.
D)The "innerness" and "outerness" of membrane surfaces are predetermined by genes.
E)Proteins can only be associated with the cell membranes on the cytoplasmic side.

Accepted Answer

The two sides of a cell membrane face different environments and carry out different functions. The outer layer faces the extracellular environment while the inner layer faces the cytoplasm. This results in different types of lipids and proteins being present on each side, which allows for different functions to be carried out on each side of the membrane.

Question 8

Which of the following is true of integral membrane proteins?
A)They lack tertiary structure.
B)They are loosely bound to the surface of the bilayer.
C)They are usually transmembrane proteins.
D)They are not mobile within the bilayer.
E)They serve only a structural role in membranes.

Accepted Answer

Integral membrane proteins are usually transmembrane proteins that span the entire lipid bilayer. This allows them to interact with both the hydrophobic tails of the phospholipids and the aqueous environment of the cytoplasm or extracellular space. Therefore, option C is the correct answer. Options A, B, D, and E are all false statements about integral membrane proteins.

Question 9

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
A)transporting ions against an electrochemical gradient
B)cell-cell recognition
C)maintaining fluidity of the phospholipid bilayer
D)attaching to the cytoskeleton
E)establishing the diffusion barrier to charged molecules

Accepted Answer

Oligosaccharides on the external surface of the plasma membrane are involved in cell-cell recognition and communication. They act as markers that identify the cell as self or nonself, which is important for processes such as immune response and tissue development. Without these markers, the cell would have difficulty communicating and interacting with other cells.

Question 10

A protein that spans the phospholipid bilayer one or more times is
A)a transmembrane protein.
B)an integral protein.
C)a peripheral protein.
D)an integrin.
E)a glycoprotein.

Accepted Answer

A protein that spans the phospholipid bilayer one or more times is called a transmembrane protein. Integral proteins are another term for transmembrane proteins. Peripheral proteins do not span the bilayer, but are instead attached to the surface of the membrane. Integrins are a type of transmembrane protein that help cells attach to the extracellular matrix. Glycoproteins are proteins that are attached to carbohydrates and can be found on both the surface and within the membrane.

Question 11

In a Paramecium, cell surface integral membrane proteins are synthesized
A)in the cytoplasm by free ribosomes.
B)by ribosomes in the nucleus.
C)by ribosomes bound to the rough endoplasmic reticulum.
D)by ribosomes in the Golgi vesicles.
E)by ribosomes bound to the inner surface of the plasma membrane.

Accepted Answer

Integral membrane proteins are synthesized by ribosomes bound to the rough endoplasmic reticulum, which is responsible for protein sorting and membrane synthesis. In Paramecium, this is where the cell surface integral membrane proteins would be synthesized.

Question 12

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?
A)They can move laterally along the plane of the membrane.
B)They frequently flip-flop from one side of the membrane to the other.
C)They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.
D)They are free to depart from the membrane and dissolve in the surrounding solution.
E)They have hydrophilic tails in the interior of the membrane.

Accepted Answer

According to the fluid mosaic model, membrane phospholipids can move laterally along the plane of the membrane, which contributes to the fluidity of the membrane. Option B is incorrect because although phospholipids can move laterally, the flip-flop motion is rare or requires the assistance of specific proteins. Option C is incorrect because membrane proteins are embedded within the lipid bilayer. Option D is incorrect because phospholipids are an essential component of the membrane and cannot depart from it. Option E is incorrect because the hydrophilic heads of phospholipids are oriented towards the exterior and interior of the membrane, while the hydrophobic tails are in the interior of the membrane.

Question 13

Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?
A)transmembrane proteins
B)integral proteins
C)peripheral proteins
D)integrins
E)glycoproteins

Accepted Answer

Peripheral proteins are not embedded within the hydrophobic portion of the lipid bilayer at all. They are attached to the surface of the membrane through noncovalent bonds and interact with integral proteins or the polar head groups of membrane lipids.

Question 14

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are
A)peripheral proteins.
B)phospholipids.
C)carbohydrates.
D)integral proteins.
E)cholesterol molecules.

Accepted Answer

Integral proteins are embedded within the phospholipid bilayer and will remain associated with one half of the membrane after it is freeze-fractured, resulting in the bumps that are observed in the electron micrograph. Peripheral proteins and carbohydrates are located on the surface of the membrane and will not necessarily be associated with the fractured surface of the bilayer. Phospholipids are the main components of the membrane and will be present on both halves after the fracture. Cholesterol molecules are also embedded within the bilayer but are not typically observed in freeze-fracture electron microscopy.

Question 15

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
A)the integral membrane proteins are not strong enough to hold the bilayer together.
B)water that is present in the middle of the bilayer freezes and is easily fractured.
C)hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing.
D)the carbon-carbon bonds of the phospholipid tails are easily broken.
E)the hydrophobic interactions that hold the membrane together are weakest at this point.

Accepted Answer

The hydrophobic interactions between the nonpolar fatty acid tails are weakest at the center of the bilayer, which is where the membrane tends to break when frozen and fractured.

Question 16

The fluid mosaic model of the membrane proposes that membranes
A)are a phospholipid bilayer.
B)are a phospholipid bilayer between two layers of hydrophilic proteins.
C)are a single layer of phospholipids and proteins.
D)consist of protein molecules embedded in a fluid bilayer of phospholipids.
E)consist of a mosaic of polysaccharides and proteins.

Accepted Answer

The fluid mosaic model of the membrane proposes that membranes consist of protein molecules embedded in a fluid bilayer of phospholipids. This model suggests that the membrane is flexible and dynamic, with molecules able to move within the lipid bilayer. This is consistent with the observed behavior of membranes in vivo.

Question 17

The formulation of a model for a structure or for a process serves which of the following purposes?
A)It asks a scientific question.
B)It functions as a testable hypothesis.
C)It records observations.
D)It serves as a data point among results.
E)It can only be arrived at after years of experimentation.

Accepted Answer

The formulation of a model for a structure or process serves as a testable hypothesis. A model is a simplified representation of a system or process that can be tested through experiments or observation. Therefore, it can be used to generate predictions that can be tested through empirical data.

Question 18

The cell membranes of Antarctic ice fish might have which of the following adaptations?
A)very long chain fatty acids
B)branched isoprenoid lipids
C)a high percentage of polyunsaturated fatty acids
D)a higher percentage of trans-fatty acids
E)no cholesterol

Accepted Answer

The cell membranes of Antarctic ice fish have a high percentage of polyunsaturated fatty acids, which enables them to remain fluid at low temperatures, allowing for proper cellular function in their cold environment.

Question 19

Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?
A)by increasing the percentage of unsaturated phospholipids in the membrane
B)by increasing the percentage of cholesterol molecules in the membrane
C)by decreasing the number of hydrophobic proteins in the membrane
D)by cotransport of glucose and hydrogen
E)by using active transport

Accepted Answer

Increasing the percentage of unsaturated phospholipids in the membrane allows it to remain fluid at colder temperatures because unsaturated fatty acids have kinks in their tails that prevent them from packing tightly together, making the membrane more fluid. Cholesterol can also help maintain fluidity, but it is not typically present in plant membranes like those of winter wheat. Choices C, D, and E are unrelated to membrane fluidity in cold temperatures.

Question 20

In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?
A)The membrane is only fluid across a very narrow temperature range.
B)Proteins rarely move, even though they possibly can do so.
C)Unsaturated lipids are excluded from the membranes.
D)The concentration of protein molecules is now known to be much higher.
E)The proteins are known to be made of only acidic amino acids.

Accepted Answer

The fluid mosaic model has been updated to reflect that the concentration of proteins in the membrane is much higher than initially thought. This adjustment acknowledges the complex and dense protein network within the membrane, which plays crucial roles in various cellular processes.

Quiz 7: Membrane Structure and Function

The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is

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

Which of the following types of molecules are the major structural components of the cell membrane?

The presence of cholesterol in the plasma membranes of some animals

In order for a protein to be an integral membrane protein, it would have to be

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

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

Which of the following is true of integral membrane proteins?

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?

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

In a Paramecium, cell surface integral membrane proteins are synthesized

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

Which of these are not embedded in the hydrophobic portion of the lipid bilayer at all?

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are

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 fluid mosaic model of the membrane proposes that membranes

The formulation of a model for a structure or for a process serves which of the following purposes?

The cell membranes of Antarctic ice fish might have which of the following adaptations?

Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?

In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?