Chapter 7 Test - AP Biology
- 1.
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
Correct Answer
C. Phospholipids and proteinsExplanation
Phospholipids and proteins are the major structural components of the cell membrane. Phospholipids form a lipid bilayer that makes up the basic structure of the membrane, with their hydrophilic heads facing outward and hydrophobic tails facing inward. Proteins are embedded within this lipid bilayer, serving various functions such as transport, communication, and structural support. Together, phospholipids and proteins create a selectively permeable barrier that regulates the movement of molecules in and out of the cell.Rate this question:
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- 2.
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.
Correct Answer
E. The hydrophobic interactions that hold the membrane together are weakest at this point.Explanation
When biological membranes are frozen and fractured, they tend to break along the middle of the bilayer because the hydrophobic interactions that hold the membrane together are weakest at this point.Rate this question:
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- 3.
All of the following molecules are part of the cell membrane except
- A.
Lipids.
- B.
Nucleic acids.
- C.
Proteins.
- D.
Phosphate groups.
- E.
Steroids.
Correct Answer
B. Nucleic acids.Explanation
The cell membrane is primarily composed of lipids, proteins, and phosphate groups. These molecules work together to form a selectively permeable barrier that regulates the movement of substances in and out of the cell. Steroids, although not explicitly mentioned in the question, are a type of lipid and therefore are part of the cell membrane. Nucleic acids, on the other hand, are not a major component of the cell membrane. They are mainly found in the nucleus and are responsible for storing and transmitting genetic information.Rate this question:
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- 4.
The original model for the bilayer structure of cell membranes, which was prepared in the 1920s, was based on which of the following?
- A.
Detailed electron micrographs of freeze-fractured membranes
- B.
The presence of proteins as a functional component of biological membranes
- C.
The observation that all membranes contain phospholipids and proteins
- D.
The understanding that phospholipids are amphipathic molecules
Correct Answer
D. The understanding that phospholipids are amphipathic moleculesExplanation
The original model for the bilayer structure of cell membranes was based on the understanding that phospholipids are amphipathic molecules. This means that they have both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. The model proposed that phospholipids arrange themselves in a double layer, with the hydrophilic heads facing the aqueous environment on both sides and the hydrophobic tails facing each other in the interior. This model provided a plausible explanation for the selective permeability and fluidity of cell membranes. The other options, such as electron micrographs and the presence of proteins, may have contributed to the understanding of cell membranes but were not the basis for the original model.Rate this question:
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- 5.
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.
Correct Answer
A. Enables the membrane to stay fluid more easily when cell temperature drops.Explanation
Cholesterol is a lipid molecule that is present in the plasma membranes of some animals. It plays a crucial role in maintaining the fluidity of the membrane. At lower temperatures, the phospholipids in the membrane tend to pack closely together, making the membrane less fluid. However, the presence of cholesterol prevents this packing by inserting itself between the phospholipids, thus maintaining the fluidity of the membrane even at lower temperatures. This is important for the proper functioning of the cell, as a more fluid membrane allows for the movement of molecules and facilitates various cellular processes.Rate this question:
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- 6.
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.
Correct Answer
A. They can move laterally along the plane of the membrane.Explanation
The fluid mosaic model of cell membranes states that phospholipids are able to move laterally along the plane of the membrane. This means that the phospholipids can freely move within the membrane, allowing for flexibility and fluidity. This movement is possible due to the fluid nature of the phospholipid bilayer. The other options are not true statements about membrane phospholipids according to the fluid mosaic model.Rate this question:
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- 7.
The lateral mobility (fluidity) of lipids and proteins in membranes is a consequence of
- A.
Lack of covalent bonds between the lipid and protein components of the membrane.
- B.
Weak hydrophobic interactions among the components in the interior of the membrane.
- C.
The presence of liquid water in the interior of the membrane.
- D.
Lack of covalent bonds between the lipids and proteins and weak hydrophobic interactions among the components in the interior of the membrane and
- E.
Lack of covalent bonds between lipids and proteins, weak hydrophobic interactions in the interior of the membrane, and the presence of liquid water in the interior of the membrane.
Correct Answer
D. Lack of covalent bonds between the lipids and proteins and weak hydrophobic interactions among the components in the interior of the membrane andExplanation
The correct answer is a combination of lack of covalent bonds between the lipids and proteins and weak hydrophobic interactions among the components in the interior of the membrane. This is because covalent bonds would restrict the movement of the lipids and proteins, while weak hydrophobic interactions allow for lateral movement within the membrane. The presence of liquid water in the interior of the membrane is not directly related to the lateral mobility of lipids and proteins.Rate this question:
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- 8.
What 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 increasing the percentage of unsaturated phospholipids and increasing the percentage of cholesterol molecules in the membrane
- E.
By increasing the percentage of unsaturated phospholipids, increasing the percentage of cholesterol molecules, and decreasing the number of hydrophobic proteins in the membrane
Correct Answer
A. By increasing the percentage of unsaturated phospholipids in the membraneExplanation
One of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold is by increasing the percentage of unsaturated phospholipids in the membrane. Unsaturated phospholipids have double bonds in their fatty acid tails, which creates kinks in the structure of the membrane. These kinks prevent the phospholipids from packing tightly together, maintaining the fluidity of the membrane even at low temperatures. By increasing the percentage of unsaturated phospholipids, the membrane is able to adapt and remain functional in extremely cold conditions.Rate this question:
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- 9.
The surface of an integral membrane protein would be best described as
- A.
Hydrophilic.
- B.
Hydrophobic.
- C.
Amphipathic.
- D.
Completely covered with phospholipids.
- E.
Exposed on only one surface of the membrane.
Correct Answer
C. Amphipathic.Explanation
The surface of an integral membrane protein is best described as amphipathic because it contains both hydrophilic and hydrophobic regions. This allows the protein to interact with both the aqueous environment inside and outside of the cell membrane. The hydrophilic regions are attracted to water, while the hydrophobic regions repel water. This unique property of amphipathic proteins is crucial for their function in transporting molecules across the membrane and maintaining the integrity of the cell membrane.Rate this question:
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- 10.
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.
Correct Answer
D. Integral proteins.Explanation
When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. This process exposes the internal structures of the membrane, including the integral proteins. Integral proteins are embedded within the phospholipid bilayer and are responsible for various functions such as transporting molecules across the membrane and cell signaling. The bumps seen on the fractured surface of the membrane in an electron micrograph are the integral proteins, indicating their presence and distribution within the membrane structure.Rate this question:
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- 11.
All of the following are functions of integral membrane proteins except
- A.
Protein synthesis.
- B.
Active transport.
- C.
Hormone reception.
- D.
Cell adhesion.
- E.
Cytoskeleton attachment.
Correct Answer
A. Protein synthesis.Explanation
Integral membrane proteins are proteins that are embedded within the lipid bilayer of cell membranes. They play a crucial role in various cellular functions such as active transport, hormone reception, cell adhesion, and cytoskeleton attachment. However, protein synthesis is not a function of integral membrane proteins. Protein synthesis occurs in the ribosomes, which are either free in the cytoplasm or attached to the endoplasmic reticulum. Therefore, the correct answer is protein synthesis.Rate this question:
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- 12.
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 a kink in the fatty acid tail, forcing adjacent lipids to be further apart.
- B.
Unsaturated fatty acids have a higher cholesterol content.
- C.
Unsaturated fatty acids permit more water in the interior of the membrane.
- D.
The double bonds block interaction among the hydrophilic head groups of the lipids.
- E.
The double bonds result in a shorter fatty acid tail.
Correct Answer
A. The double bonds form a kink in the fatty acid tail, forcing adjacent lipids to be further apart.Explanation
The presence of double bonds in unsaturated fatty acids causes a kink in the fatty acid tail. This kink forces the adjacent lipids to be further apart from each other. As a result, the overall structure of the lipid bilayer is disrupted, making it more fluid at lower temperatures. This increased fluidity allows for better movement of molecules and maintains the functionality of the membrane even in colder conditions.Rate this question:
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- 13.
Which of the following is correct about 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.
Correct Answer
C. They are usually transmembrane proteins.Explanation
Integral membrane proteins are usually transmembrane proteins, meaning they span across the entire lipid bilayer of the cell membrane. They have both hydrophobic and hydrophilic regions, allowing them to interact with the hydrophobic interior of the lipid bilayer as well as the aqueous environment both inside and outside of the cell. These proteins play a variety of roles in the cell, including transport of molecules across the membrane, cell signaling, and enzymatic activity, among others. They are not loosely bound to the surface of the bilayer, lack tertiary structure, or serve only a structural role in membranes. They can also exhibit mobility within the bilayer.Rate this question:
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- 14.
Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes?
- A.
Facilitated diffusion of molecules down their concentration gradients
- B.
Active transport of molecules against their concentration gradients
- C.
Maintaining the integrity of a fluid mosaic membrane
- D.
Maintaining membrane fluidity at low temperatures
- E.
A cell's ability to distinguish one type of neighboring cell from another
Correct Answer
E. A cell's ability to distinguish one type of neighboring cell from another -
- 15.
What is one of the functions of cholesterol in animal cell membranes?
- A.
Facilitates transport of ions
- B.
Stores energy
- C.
Maintains membrane fluidity
- D.
Speeds diffusion
- E.
Phosphorylates ADP
Correct Answer
C. Maintains membrane fluidityExplanation
Cholesterol plays a crucial role in maintaining the fluidity of animal cell membranes. It helps regulate the fluidity by preventing the fatty acid chains of phospholipids in the membrane from packing too closely together. This prevents the membrane from becoming too rigid or too fluid, which could disrupt its integrity and function. By maintaining the appropriate fluidity, cholesterol ensures that the membrane remains flexible enough for various cellular processes, such as membrane transport and signal transduction, to occur efficiently.Rate this question:
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- 16.
What membrane-surface molecules are thought to be most important as cells recognize each other?
- A.
Phospholipids
- B.
Integral proteins
- C.
Peripheral proteins
- D.
Cholesterol
- E.
Glycoproteins
Correct Answer
E. GlycoproteinsExplanation
Glycoproteins are thought to be the most important membrane-surface molecules as cells recognize each other. These molecules are proteins that have attached carbohydrate chains. The carbohydrates on glycoproteins can act as recognition markers, allowing cells to identify and interact with each other. This recognition is crucial for various cellular processes such as immune response, cell adhesion, and cell signaling. Phospholipids, integral proteins, peripheral proteins, and cholesterol are also important components of cell membranes, but glycoproteins specifically play a key role in cell recognition.Rate this question:
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- 17.
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
Correct Answer
B. Cell-cell recognitionExplanation
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in cell-cell recognition. Oligosaccharides on the cell surface act as markers that allow cells to recognize and communicate with each other. Without these markers, the cell would have difficulty identifying and interacting with other cells, which is essential for various cellular processes such as immune response, tissue development, and cell signaling.Rate this question:
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- 18.
Which of the following adheres to the extracellular surface of animal cell plasma membranes?
- A.
Fibers of the extracellular matrix
- B.
Fibers of the cytoskeleton
- C.
The phospholipid bilayer
- D.
Cholesterol
- E.
Carrier proteins
Correct Answer
A. Fibers of the extracellular matrixExplanation
The extracellular matrix is a network of fibers that provides structural support to animal cells. It is located on the outside of the plasma membrane and helps to anchor cells together. The other options, such as the cytoskeleton, phospholipid bilayer, cholesterol, and carrier proteins, are all components found within the cell or embedded in the plasma membrane, not on the extracellular surface. Therefore, the correct answer is fibers of the extracellular matrix.Rate this question:
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- 19.
What kinds of molecules pass through a cell membrane most easily?
- A.
Large and hydrophobic
- B.
Small and hydrophobic
- C.
Large polar
- D.
Ionic
- E.
Monosaccharides such as glucose
Correct Answer
B. Small and hydrophobicExplanation
Small and hydrophobic molecules are able to pass through a cell membrane most easily because the cell membrane is made up of a phospholipid bilayer. This bilayer consists of hydrophobic tails that repel water and create a barrier, while the hydrophilic heads face the watery environment inside and outside the cell. Small and hydrophobic molecules can easily dissolve in the hydrophobic region of the membrane and pass through it, while larger polar and ionic molecules have difficulty crossing the hydrophobic barrier. Monosaccharides such as glucose, although small, are polar molecules and therefore have a harder time passing through the cell membrane compared to small and hydrophobic molecules.Rate this question:
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- 20.
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
- A.
It is a peripheral membrane protein.
- B.
It exhibits a specificity for a particular type of molecule.
- C.
It requires the expenditure of cellular energy to function.
- D.
It works against diffusion.
- E.
It has few, if any, hydrophobic amino acids.
Correct Answer
B. It exhibits a specificity for a particular type of molecule.Explanation
A characteristic feature of a carrier protein in a plasma membrane is that it exhibits a specificity for a particular type of molecule. Carrier proteins are responsible for transporting specific molecules across the plasma membrane, and they do so by binding to the molecule and undergoing a conformational change to transport it across the membrane. This specificity allows carrier proteins to selectively transport certain molecules while excluding others.Rate this question:
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- 21.
After a membrane freezes and then thaws, it often becomes leaky to solutes. The most reasonable explanation for this is that
- A.
Transport proteins become nonfunctional during freezing.
- B.
The lipid bilayer loses its fluidity when it freezes.
- C.
Aquaporins can no longer function after freezing.
- D.
The integrity of the lipid bilayer is broken when the membrane freezes.
- E.
The solubility of most solutes in the cytoplasm decreases on freezing.
Correct Answer
D. The integrity of the lipid bilayer is broken when the membrane freezes.Explanation
When a membrane freezes and then thaws, the most reasonable explanation for it becoming leaky to solutes is that the integrity of the lipid bilayer is broken. Freezing causes the water molecules within the membrane to expand and form ice crystals, which can disrupt the structure of the lipid bilayer. As a result, gaps or holes may form in the membrane, allowing solutes to pass through more easily. This explanation is supported by the fact that transport proteins, aquaporins, and the solubility of solutes in the cytoplasm are not directly related to the integrity of the lipid bilayer.Rate this question:
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- 22.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
- A.
CO2
- B.
An amino acid
- C.
Glucose
- D.
K+
- E.
Starch
Correct Answer
A. CO2Explanation
CO2 would likely move through the lipid bilayer of a plasma membrane most rapidly because it is a small, nonpolar molecule. The lipid bilayer is made up of phospholipids, which have hydrophobic tails that repel polar molecules like amino acids, glucose, and K+. However, CO2 is nonpolar and can easily dissolve in the lipid bilayer, allowing it to pass through rapidly. Starch, on the other hand, is a large, polar molecule that cannot easily pass through the hydrophobic interior of the lipid bilayer.Rate this question:
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- 23.
The selective permeability of biological membranes is dependent on which of the following?
- A.
The type of transport proteins that are present in the membrane
- B.
The lipid bilayer being permeable to primarily small, nonpolar molecules
- C.
The types of carbohydrates on the surface of the membrane
- D.
The type of transport proteins that are present in the membrane and the lipid bilayer being permeable to primarily small, nonpolar molecules
- E.
The type of transport proteins that are present in the membrane, the lipid bilayer being permeable to primarily small, nonpolar molecules, and the types of carbohydrates on the surface of the membrane
Correct Answer
D. The type of transport proteins that are present in the membrane and the lipid bilayer being permeable to primarily small, nonpolar moleculesExplanation
The correct answer is the type of transport proteins that are present in the membrane and the lipid bilayer being permeable to primarily small, nonpolar molecules. This is because transport proteins play a crucial role in facilitating the movement of specific molecules across the membrane. They can be selective and only allow certain molecules to pass through. Additionally, the lipid bilayer itself is composed of nonpolar fatty acid tails, which makes it impermeable to polar molecules but allows small, nonpolar molecules to pass through easily. Therefore, the combination of specific transport proteins and the permeability of the lipid bilayer determines the selective permeability of biological membranes.Rate this question:
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- 24.
Which of the following statements is correct about diffusion?
- A.
It is very rapid over long distances.
- B.
It requires an expenditure of energy by the cell.
- C.
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
- D.
It is an active process in which molecules move from a region of lower concentration to one of higher concentration.
- E.
It requires integral proteins in the cell membrane.
Correct Answer
C. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.Explanation
Diffusion is a passive process in which molecules move from a region of higher concentration to a region of lower concentration. This means that molecules naturally move down their concentration gradient, without the need for any energy expenditure by the cell. It is a fundamental process that allows for the movement of molecules and ions across cell membranes and is essential for various biological processes. Unlike active transport, diffusion does not require integral proteins in the cell membrane.Rate this question:
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- 25.
Water passes quickly through cell membranes because
- A.
The bilayer is hydrophilic.
- B.
It moves through hydrophobic channels.
- C.
Water movement is tied to ATP hydrolysis.
- D.
It is a small, polar, charged molecule.
- E.
It moves through aquaporins in the membrane.
Correct Answer
E. It moves through aquaporins in the membrane.Explanation
Water passes quickly through cell membranes because it moves through aquaporins in the membrane. Aquaporins are specialized channel proteins that facilitate the rapid movement of water molecules across the hydrophobic interior of the cell membrane. These proteins create a pathway for water to pass through, allowing it to move efficiently and quickly.Rate this question:
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- 26.
A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water, equal to the volume of blood lost, is transferred directly into one of his veins. What will be the most probable result of this transfusion?
- A.
It will have no unfavorable effect as long as the water is free of viruses and bacteria.
- B.
The patient's red blood cells will shrivel up because the blood fluid is hypotonic compared to the cells.
- C.
The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.
- D.
The patient's red blood cells will shrivel up because the blood fluid is hypertonic compared to the cells.
- E.
The patient's red blood cells will burst because the blood fluid is hypertonic compared to the cells.
Correct Answer
C. The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.Explanation
When distilled water, which is hypotonic compared to the cells, is transferred directly into the patient's veins, it will cause the red blood cells to swell. This is because the concentration of solutes inside the cells is higher than that of the water being infused, leading to an osmotic gradient that drives water into the cells. As a result, the red blood cells will take in water and expand, potentially causing them to burst if the swelling becomes too severe.Rate this question:
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- 27.
Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a salt solution become limp and soft. From this we can deduce that the cells of the celery stalks are
- A.
Hypotonic to both fresh water and the salt solution.
- B.
Hypertonic to both fresh water and the salt solution.
- C.
Hypertonic to fresh water but hypotonic to the salt solution.
- D.
Hypotonic to fresh water but hypertonic to the salt solution.
- E.
Isotonic with fresh water but hypotonic to the salt solution.
Correct Answer
C. Hypertonic to fresh water but hypotonic to the salt solution.Explanation
The cells of the celery stalks are hypertonic to fresh water because when immersed in fresh water, they become stiff and hard. This indicates that water is entering the cells, causing them to expand and become turgid. On the other hand, the cells are hypotonic to the salt solution because when immersed in it, they become limp and soft. This suggests that water is leaving the cells, causing them to shrink and lose their turgidity. Therefore, the cells of the celery stalks are hypertonic to fresh water but hypotonic to the salt solution.Rate this question:
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- 28.
A cell whose cytoplasm has a concentration of 0.02 molar glucose is placed in a test tube of water containing 0.02 molar glucose. Assuming that glucose is not actively transported into the cell, which of the following terms describes the tonicity of the external solution relative to the cytoplasm of the cell?
- A.
Isotonic
- B.
Hypertonic
- C.
Hypotonic
- D.
Flaccid
- E.
Turgid
Correct Answer
A. IsotonicExplanation
The external solution has the same concentration of glucose as the cytoplasm of the cell, which means there is no net movement of water across the cell membrane. This indicates that the tonicity of the external solution is isotonic relative to the cytoplasm of the cell.Rate this question:
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- 29.
Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
- A.
The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution.
- B.
The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution.
- C.
The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution.
- D.
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
- E.
The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution.
Correct Answer
D. The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.Explanation
In a hypotonic solution, the concentration of solutes outside the cell is lower than inside the cell. This causes water to move into the cell, resulting in the animal cell being in a hypotonic solution. On the other hand, in an isotonic solution, the concentration of solutes outside the cell is the same as inside the cell, leading to no net movement of water. This is the case for the animal cell. In a hypotonic solution, the concentration of solutes outside the cell is higher than inside the cell. This causes water to move out of the cell, resulting in the plant cell being in a hypotonic solution. Therefore, the correct statement is that the animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.Rate this question:
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- 30.
You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would not be a factor that determines whether the molecule enters the cell?
- A.
Size of the drug molecule
- B.
Polarity of the drug molecule
- C.
Charge on the drug molecule
- D.
Similarity of the drug molecule to other molecules transported by the target cells
- E.
Lipid composition of the target cells' plasma membrane
Correct Answer
E. Lipid composition of the target cells' plasma membraneExplanation
The lipid composition of the target cells' plasma membrane would not be a factor that determines whether the molecule enters the cell. The lipid composition refers to the types and proportions of different lipids present in the plasma membrane, which primarily affects the fluidity and stability of the membrane. However, the ability of a molecule to enter the cell is determined by factors such as its size, polarity, charge, and similarity to other molecules transported by the target cells.Rate this question:
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- 31.
All of the following membrane activities require energy from ATP hydrolysis except
- A.
Facilitated diffusion.
- B.
Active transport.
- C.
Na+ ions moving out of the cell.
- D.
Proton pumps.
- E.
Translocation of potassium into a cell.
Correct Answer
A. Facilitated diffusion.Explanation
Facilitated diffusion is the process by which molecules pass through a cell membrane with the help of transport proteins, but without the need for ATP hydrolysis. In facilitated diffusion, the molecules move down their concentration gradient, from an area of high concentration to an area of low concentration. On the other hand, active transport, Na+ ions moving out of the cell, proton pumps, and translocation of potassium into a cell all require ATP hydrolysis to move molecules against their concentration gradient, from an area of low concentration to an area of high concentration.Rate this question:
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- 32.
What are the membrane structures that function in active transport?
- A.
Peripheral proteins
- B.
Carbohydrates
- C.
Cholesterol
- D.
Cytoskeleton filaments
- E.
Integral proteins
Correct Answer
E. Integral proteinsExplanation
Integral proteins are membrane structures that function in active transport. They are embedded within the lipid bilayer of the cell membrane and play a crucial role in transporting molecules across the membrane against their concentration gradient. These proteins have specific binding sites for the molecules they transport and undergo conformational changes to facilitate the movement of these molecules across the membrane. Peripheral proteins, carbohydrates, cholesterol, and cytoskeleton filaments are not directly involved in active transport.Rate this question:
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- 33.
The movement of a substance across a biological membrane against its concentration gradient with the help of energy input is
- A.
Diffusion.
- B.
Active transport.
- C.
Osmosis.
- D.
Facilitated diffusion.
- E.
Exocytosis.
Correct Answer
B. Active transport.Explanation
Active transport is the process in which a substance is moved across a biological membrane against its concentration gradient, meaning from an area of lower concentration to an area of higher concentration. This process requires the input of energy, usually in the form of ATP. Diffusion, osmosis, and facilitated diffusion do not involve the movement of substances against their concentration gradients, and exocytosis refers to the release of substances from a cell rather than their movement across a membrane. Therefore, the correct answer is active transport.Rate this question:
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- 34.
Carrier molecules in the membrane and metabolic energy are required for
- A.
Osmosis.
- B.
Facilitated diffusion.
- C.
Active transport.
- D.
Facilitated diffusion and active transport.
- E.
Facilitated diffusion, active transport, and osmosis.
Correct Answer
C. Active transport.Explanation
Active transport is the process by which cells move molecules or ions across the cell membrane against their concentration gradient, requiring the use of carrier molecules in the membrane and metabolic energy. Osmosis, on the other hand, is the passive movement of water molecules across a selectively permeable membrane, and facilitated diffusion is the passive movement of molecules across a membrane with the help of specific carrier proteins. Therefore, active transport is the only process that requires both carrier molecules and metabolic energy.Rate this question:
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- 35.
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?
- A.
Simple diffusion
- B.
Phagocytosis
- C.
Active transport pumps
- D.
Exocytosis
- E.
Facilitated diffusion
Correct Answer
E. Facilitated diffusionExplanation
The cells lining the small intestine rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. This indicates that the movement of glucose is not solely relying on simple diffusion, as glucose diffuses slowly through artificial phospholipid bilayers. Phagocytosis and exocytosis are not involved in the transport of glucose. Active transport pumps require energy to move substances against their concentration gradient, which is not mentioned in the given information. Therefore, the most probable transport mechanism functioning in the intestinal cells is facilitated diffusion, where specific carrier proteins assist in the movement of glucose across the cell membrane.Rate this question:
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- 36.
The main difference(s) between facilitated diffusion and active transport is (are)
- A.
Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient.
- B.
Facilitated diffusion does not rely on cellular energy and active transport does.
- C.
Facilitated diffusion uses channel or carrier proteins and active transport does not.
- D.
Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient and does not rely on cellular energy and active transport does.
- E.
Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient, facilitated transport does not rely on cellular energy and active transport does, and facilitated transport uses channel or carrier proteins and active transport does not.
Correct Answer
E. Facilitated diffusion moves substances down their concentration gradient and active transport moves them against their gradient, facilitated transport does not rely on cellular energy and active transport does, and facilitated transport uses channel or carrier proteins and active transport does not.Explanation
Facilitated diffusion and active transport have several main differences. Firstly, facilitated diffusion moves substances down their concentration gradient, while active transport moves them against their gradient. Additionally, facilitated diffusion does not rely on cellular energy, whereas active transport does. Furthermore, facilitated diffusion uses channel or carrier proteins to transport substances, while active transport does not rely on these proteins. Therefore, the correct answer is that facilitated diffusion moves substances down their concentration gradient, does not rely on cellular energy, and uses channel or carrier proteins, while active transport moves substances against their gradient, relies on cellular energy, and does not use channel or carrier proteins.Rate this question:
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- 37.
What is the voltage across a membrane called?
- A.
Water potential
- B.
Chemical gradient
- C.
Membrane potential
- D.
Osmotic potential
- E.
Electrochemical gradient
Correct Answer
C. Membrane potentialExplanation
The voltage across a membrane is called the membrane potential. This refers to the electrical potential difference that exists between the inside and outside of a cell or organelle, caused by the uneven distribution of ions across the membrane. It plays a crucial role in various cellular processes, including the transmission of nerve impulses and the movement of ions and molecules across the membrane.Rate this question:
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- 38.
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
- A.
Cotransport proteins.
- B.
Ion channels.
- C.
Carrier proteins.
- D.
Ion channels and carrier proteins.
- E.
Cotransport proteins, ion channels, and carrier proteins.
Correct Answer
A. Cotransport proteins.Explanation
The electrochemical gradients of many ions across the plasma membrane are most likely accounted for by cotransport proteins. These proteins use the energy from the movement of one molecule down its concentration gradient to transport another molecule against its concentration gradient. This allows for the establishment of concentration gradients for multiple ions, even though there are only one or two electrogenic pumps present in the membrane.Rate this question:
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- 39.
The sodium-potassium pump is called an electrogenic pump because it
- A.
Pumps equal quantities of Na+ and K+ across the membrane.
- B.
Pumps hydrogen ions out of the cell.
- C.
Contributes to the membrane potential.
- D.
Ionizes sodium and potassium atoms.
- E.
Is used to drive the transport of other molecules against a concentration gradient.
Correct Answer
C. Contributes to the membrane potential.Explanation
The sodium-potassium pump is called an electrogenic pump because it contributes to the membrane potential. This pump actively transports three sodium ions out of the cell and two potassium ions into the cell. This creates an imbalance of positive charges, with more positive charges outside the cell than inside. This difference in charge across the cell membrane is what creates the membrane potential, which is essential for various cellular processes such as nerve impulses and muscle contractions.Rate this question:
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- 40.
If a membrane protein in an animal cell is involved in the cotransport of glucose and sodium ions into the cell, which of the following is most likely not true?
- A.
The sodium ions are moving down their electrochemical gradient.
- B.
Glucose is entering the cell against its concentration gradient.
- C.
Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.
- D.
The higher sodium ion concentration outside the cell is the result of an electrogenic pump.
- E.
A substance that blocked sodium ions from binding to the cotransport protein would also block the transport of glucose.
Correct Answer
C. Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.Explanation
The statement "Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell" is most likely not true. This is because the cotransporter is specifically involved in the cotransport of glucose and sodium ions, suggesting that the movement of sodium ions is dependent on the presence of glucose. Therefore, if glucose is not present outside the cell, it is unlikely that sodium ions would be able to move down their electrochemical gradient through the cotransporter.Rate this question:
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- 41.
The movement of potassium into an animal cell requires
- A.
Low cellular concentrations of sodium.
- B.
High cellular concentrations of potassium.
- C.
An energy source such as ATP or a proton gradient.
- D.
A cotransport protein.
- E.
A gradient of protons across the plasma membrane.
Correct Answer
C. An energy source such as ATP or a proton gradient.Explanation
The movement of potassium into an animal cell requires an energy source such as ATP or a proton gradient. This is because potassium ions are positively charged and therefore require energy to move against their concentration gradient into the cell. ATP provides the necessary energy for active transport of potassium ions, while a proton gradient can also drive the movement of potassium ions through facilitated diffusion. Both mechanisms require energy to transport potassium into the cell.Rate this question:
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- 42.
Ions diffuse across membranes down their
- A.
Chemical gradients.
- B.
Concentration gradients.
- C.
Electrical gradients.
- D.
Electrochemical gradients.
- E.
Concentration gradients and chemical gradients.
Correct Answer
D. Electrochemical gradients.Explanation
Ions diffuse across membranes down their electrochemical gradients. This means that they move from areas of higher concentration to areas of lower concentration, as well as from areas of higher electrical charge to areas of lower electrical charge. This combined effect of concentration and electrical gradients determines the direction and rate of ion movement across the membrane.Rate this question:
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- 43.
Which of the following characterizes the sodium-potassium pump?
- A.
Sodium ions are pumped out of a cell against their gradient.
- B.
Potassium ions are pumped into a cell against their gradient.
- C.
The pump protein undergoes a conformational change.
- D.
Sodium ions are pumped out of a cell against their gradient and potassium ions are pumped into a cell against their gradient.
- E.
Sodium ions are pumped out of a cell against their gradient, potassium ions are pumped into a cell against their gradient, and the pump protein undergoes a conformational change.
Correct Answer
E. Sodium ions are pumped out of a cell against their gradient, potassium ions are pumped into a cell against their gradient, and the pump protein undergoes a conformational change.Explanation
The sodium-potassium pump is a transport protein found in the cell membrane that actively transports sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients. This process requires energy in the form of ATP and is essential for maintaining the electrochemical gradient across the cell membrane. Additionally, the pump protein undergoes a conformational change during the transport process, allowing it to alternate between binding and releasing sodium and potassium ions.Rate this question:
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- 44.
What mechanisms do plants use to load sucrose produced by photosynthesis into specialized cells in the veins of leaves?
- A.
An electrogenic pump
- B.
A proton pump
- C.
A contransport protein
- D.
An electrogenic pump and a contransport protein
- E.
An electrogenic pump, a proton pump, and a contransport protein
Correct Answer
E. An electrogenic pump, a proton pump, and a contransport proteinExplanation
Plants use multiple mechanisms to load sucrose produced by photosynthesis into specialized cells in the veins of leaves. One mechanism is an electrogenic pump, which helps create an electrical potential difference across the cell membrane. Another mechanism is a proton pump, which transports protons across the membrane. Additionally, plants use a cotransport protein, which helps transport sucrose along with other ions or molecules. These three mechanisms work together to efficiently load sucrose into the specialized cells in the veins of leaves.Rate this question:
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- 45.
The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on?
- A.
It will be on the cytoplasmic side of the ER.
- B.
It will be on the side facing the interior of the ER.
- C.
It could be facing in either direction because the orientation of proteins is scrambled in the Golgi apparatus.
- D.
It doesn't matter, because the pump is not active in the ER.
- E.
Not enough information is provided to answer this question.
Correct Answer
A. It will be on the cytoplasmic side of the ER.Explanation
The correct answer is that the ATP binding site will be on the cytoplasmic side of the ER. This is because the sodium-potassium pump requires cytoplasmic ATP to function, indicating that the ATP binding site needs to be accessible from the cytoplasmic side of the ER membrane.Rate this question:
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- 46.
Which of the following statements about membrane structure and function is false?
- A.
Diffusion of gases is faster in air than across membranes.
- B.
Diffusion, osmosis, and facilitated diffusion do not require any direct energy input from the cell.
- C.
The types of proteins that are exposed on one side of a membrane are nearly identical to those exposed on the other side of the membrane.
- D.
Voltage across the membrane depends on an unequal distribution of ions across the plasma membrane.
- E.
Special membrane proteins can cotransport two solutes by coupling diffusion down a concentration gradient to transport against the concentration gradient.
Correct Answer
C. The types of proteins that are exposed on one side of a membrane are nearly identical to those exposed on the other side of the membrane.Explanation
The types of proteins that are exposed on one side of a membrane are not nearly identical to those exposed on the other side of the membrane. Membrane proteins can have different functions and structures depending on their location and role in the cell. Some proteins may be embedded in the membrane, while others may be attached to the surface. Additionally, proteins can have specific functions such as transporters, receptors, or enzymes, which can vary on each side of the membrane.Rate this question:
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- 47.
All of the following processes take material into cells except
- A.
Pinocytosis.
- B.
Endocytosis.
- C.
Exocytosis.
- D.
Active transport.
- E.
Carrier-facilitated diffusion.
Correct Answer
C. Exocytosis.Explanation
Exocytosis is the process by which cells release materials out of the cell. It involves the fusion of vesicles containing the materials with the cell membrane, causing the contents to be expelled outside of the cell. In contrast, pinocytosis, endocytosis, active transport, and carrier-facilitated diffusion all involve the uptake of materials into the cell.Rate this question:
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- 48.
An organism with a cell wall would have the most difficulty doing which process?
- A.
Diffusion
- B.
Osmosis
- C.
Active transport
- D.
Phagocytosis
- E.
Exocytosis
Correct Answer
D. PhagocytosisExplanation
An organism with a cell wall would have the most difficulty doing phagocytosis because phagocytosis is a process where a cell engulfs and internalizes solid particles or other cells. The presence of a cell wall would hinder the flexibility and ability of the organism to engulf and internalize particles, making phagocytosis difficult.Rate this question:
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- 49.
The membrane activity most nearly opposite to exocytosis is
- A.
Plasmolysis.
- B.
Osmosis.
- C.
Facilitated diffusion.
- D.
Phagocytosis.
- E.
Active transport.
Correct Answer
D. Phagocytosis.Explanation
Phagocytosis is the process by which cells engulf and internalize solid particles or large molecules. It is the opposite of exocytosis, which is the process of releasing substances from a cell. While osmosis, facilitated diffusion, and active transport are all types of membrane activities, they are not directly opposite to exocytosis. Plasmolysis, on the other hand, is the shrinkage of a cell due to the loss of water, which is unrelated to exocytosis. Therefore, phagocytosis is the most nearly opposite activity to exocytosis.Rate this question:
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- 50.
White blood cells engulf bacteria through what process?
- A.
Exocytosis
- B.
Phagocytosis
- C.
Pinocytosis
- D.
Osmosis
- E.
Receptor-mediated exocytosis
Correct Answer
B. PhagocytosisExplanation
White blood cells engulf bacteria through a process called phagocytosis. Phagocytosis is a cellular process where the cell engulfs solid particles, such as bacteria, by extending its membrane around them and forming a vesicle called a phagosome. The phagosome then fuses with lysosomes, which contain digestive enzymes, to form a phagolysosome. Within the phagolysosome, the bacteria are broken down and destroyed. This process is an important defense mechanism of the immune system to eliminate harmful pathogens.Rate this question:
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