Chapter 7 Test - AP Biology

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1/75 Questions

Which of the following statements is correct about diffusion?
- It is very rapid over long distances.
- It requires an expenditure of energy by the cell.
- It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
- It is an active process in which molecules move from a region of lower concentration to one of higher concentration.
- It requires integral proteins in the cell membrane.

About This Quiz

This Chapter 7 Test in AP Biology focuses on the structural components and properties of cell membranes. It assesses understanding of phospholipids, proteins, and the fluid mosaic model, crucial for students aiming to excel in advanced biology studies.

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2.

Which of the following types of molecules are the major structural components of the cell membrane?
- Phospholipids and cellulose
- Nucleic acids and proteins
- Phospholipids and proteins
- Proteins and cellulose
- Glycoproteins and cholesterol
Correct Answer

A. Phospholipids and proteins

Explanation

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.

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3.

What kinds of molecules pass through a cell membrane most easily?
- Large and hydrophobic
- Small and hydrophobic
- Large polar
- Ionic
- Monosaccharides such as glucose
Correct Answer

A. Small and hydrophobic

Explanation

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.

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4.

Match the labeled component of the cell membrane with its description: glycolipid
- A
- B
- C
- D
- E
Correct Answer

A. B
5.

The movement of a substance across a biological membrane against its concentration gradient with the help of energy input is
- Diffusion.
- Active transport.
- Osmosis.
- Facilitated diffusion.
- Exocytosis.
Correct Answer

A. 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.

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6.

What is one of the functions of cholesterol in animal cell membranes?
- Facilitates transport of ions
- Stores energy
- Maintains membrane fluidity
- Speeds diffusion
- Phosphorylates ADP
Correct Answer

A. Maintains membrane fluidity

Explanation

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.

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1
7.

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?
- Isotonic
- Hypertonic
- Hypotonic
- Flaccid
- Turgid
Correct Answer

A. Isotonic

Explanation

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.

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8.

All of the following processes take material into cells except
- Pinocytosis.
- Endocytosis.
- Exocytosis.
- Active transport.
- Carrier-facilitated diffusion.
Correct Answer

A. 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.

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1
9.

All of the following membrane activities require energy from ATP hydrolysis except
- Facilitated diffusion.
- Active transport.
- Na+ ions moving out of the cell.
- Proton pumps.
- 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.

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10.

The interior of the phospholipid bilayer is
- Composed of fatty acids.
- Hydrophobic.
- Composed of cholesterol.
- Hydrophilic.
- Water.
Correct Answer

A. Hydrophobic.

Explanation

The interior of the phospholipid bilayer is hydrophobic because it is composed of fatty acids. Fatty acids are nonpolar molecules, meaning they do not have a charge and are not attracted to water. This makes them repel water and form a barrier within the bilayer that prevents water-soluble substances from easily passing through.

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11.

White blood cells engulf bacteria through what process?
- Exocytosis
- Phagocytosis
- Pinocytosis
- Osmosis
- Receptor-mediated exocytosis
Correct Answer

A. Phagocytosis

Explanation

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.

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12.

Match the labeled component of the cell membrane with its description: peripheral protein
- A
- B
- C
- D
- E
Correct Answer

A. D

Explanation

The correct answer is D because a peripheral protein is a type of protein that is loosely attached to the surface of the cell membrane. It is not embedded within the lipid bilayer like integral proteins. Peripheral proteins play various roles in cell signaling, transport of molecules, and cell adhesion. They can also act as enzymes or receptors.

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13.

Oxygen crosses a plasma membrane by
- Osmosis.
- Phagocytosis.
- Active transport.
- Pinocytosis.
- Passive transport.
Correct Answer

A. Passive transport.

Explanation

Passive transport is the movement of molecules across a membrane without the need for energy. Oxygen, being a small molecule, can passively diffuse across the plasma membrane from an area of high concentration to an area of low concentration. This process is known as simple diffusion, which is a type of passive transport. Osmosis is the movement of water molecules across a membrane, not applicable to oxygen. Phagocytosis and pinocytosis involve the engulfment of particles or fluids, respectively, by the cell, which is not how oxygen crosses the plasma membrane. Active transport requires energy to move molecules against their concentration gradient, which is not the case for oxygen.

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14.

Water passes quickly through cell membranes because
- The bilayer is hydrophilic.
- It moves through hydrophobic channels.
- Water movement is tied to ATP hydrolysis.
- It is a small, polar, charged molecule.
- It moves through aquaporins in the membrane.
Correct Answer

A. 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.

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15.

The membrane activity most nearly opposite to exocytosis is
- Plasmolysis.
- Osmosis.
- Facilitated diffusion.
- Phagocytosis.
- Active transport.
Correct Answer

A. 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.

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16.

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?
- The double bonds form a kink in the fatty acid tail, forcing adjacent lipids to be further apart.
- Unsaturated fatty acids have a higher cholesterol content.
- Unsaturated fatty acids permit more water in the interior of the membrane.
- The double bonds block interaction among the hydrophilic head groups of the lipids.
- 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.

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17.

Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
- CO2
- An amino acid
- Glucose
- K+
- Starch
Correct Answer

A. CO2

Explanation

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.

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18.

Match the labeled component of the cell membrane with its description: cholesterol
- A
- B
- C
- D
- E
Correct Answer

A. E
19.

Five dialysis bags, constructed from a semi-permeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. Which line represents the bag that contained a solution isotonic to the 0.6 molar solution at the beginning of the experiment?
- A
- B
- C
- D
- E
Correct Answer

A. C

Explanation

The line that represents the bag that contained a solution isotonic to the 0.6 molar solution at the beginning of the experiment is line C. This is because an isotonic solution has the same concentration of solutes as the surrounding solution. In this case, the bag in line C showed no change in mass over time, indicating that the concentration of solutes inside the bag was the same as the concentration of solutes in the surrounding 0.6 M sucrose solution.

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20.

The presence of cholesterol in the plasma membranes of some animals
- Enables the membrane to stay fluid more easily when cell temperature drops.
- Enables the animal to remove hydrogen atoms from saturated phospholipids.
- Enables the animal to add hydrogen atoms to unsaturated phospholipids.
- Makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.
- 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.

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21.

Match the labeled component of the cell membrane with its description: fiber of the extracellular matrix
- A
- B
- C
- D
- E
Correct Answer

A. A

Explanation

The correct answer is A because the fiber of the extracellular matrix is a component of the cell membrane. It provides structural support and helps in cell adhesion and communication.

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22.

Match the labeled component of the cell membrane with its description: microfilament of the cytoskeleton
- A
- B
- C
- D
- E
Correct Answer

A. C

Explanation

C is the correct answer because microfilaments are a component of the cytoskeleton. The cytoskeleton is a network of protein filaments that provides structural support and helps with cell movement. Microfilaments, also known as actin filaments, are the thinnest filaments of the cytoskeleton and are involved in various cellular processes such as cell division, cell shape maintenance, and cell movement.

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23.

Which of the following factors would tend to increase membrane fluidity?
- A greater proportion of unsaturated phospholipids
- A greater proportion of saturated phospholipids
- A lower temperature
- A relatively high protein content in the membrane
- A greater proportion of relatively large glycolipids compared to lipids having smaller molecular masses
Correct Answer

A. A greater proportion of unsaturated phospholipids

Explanation

A greater proportion of unsaturated phospholipids would tend to increase membrane fluidity because unsaturated phospholipids have double bonds in their fatty acid tails, which introduce kinks in the hydrocarbon chains. These kinks prevent the phospholipids from packing tightly together, increasing the spaces between them and allowing for greater movement and fluidity of the membrane.

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24.

All of the following molecules are part of the cell membrane except
- Lipids.
- Nucleic acids.
- Proteins.
- Phosphate groups.
- Steroids.
Correct Answer

A. 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.

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25.

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

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26.

In what way do the various membranes of a eukaryotic cell differ?
- Phospholipids are found only in certain membranes.
- Certain proteins are unique to each membrane.
- Only certain membranes of the cell are selectively permeable.
- Only certain membranes are constructed from amphipathic molecules.
- Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.
Correct Answer

A. Certain proteins are unique to each membrane.

Explanation

The various membranes of a eukaryotic cell differ in terms of the proteins that are present in each membrane. Certain proteins are unique to each membrane, meaning that they are specific to a particular membrane and are not found in other membranes. This diversity of proteins allows each membrane to have different functions and perform specific tasks within the cell.

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27.

An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
- Transporting ions against an electrochemical gradient
- Cell-cell recognition
- Maintaining fluidity of the phospholipid bilayer
- Attaching to the cytoskeleton
- Establishing the diffusion barrier to charged molecules
Correct Answer

A. Cell-cell recognition

Explanation

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.

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28.

The movement of potassium into an animal cell requires
- Low cellular concentrations of sodium.
- High cellular concentrations of potassium.
- An energy source such as ATP or a proton gradient.
- A cotransport protein.
- A gradient of protons across the plasma membrane.
Correct Answer

A. 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.

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29.

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?
- The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution.
- The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution.
- The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution.
- The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
- The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution.
Correct Answer

A. 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.

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30.

What are the membrane structures that function in active transport?
- Peripheral proteins
- Carbohydrates
- Cholesterol
- Cytoskeleton filaments
- Integral proteins
Correct Answer

A. Integral proteins

Explanation

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.

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31.

Five dialysis bags, constructed from a semi-permeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. Which line represents the bag with the highest initial concentration of sucrose?
- A
- B
- C
- D
- E
Correct Answer

A. A

Explanation

The correct answer is A because the line representing bag A shows the highest percent change in mass over time. This indicates that the bag with the highest initial concentration of sucrose is losing the most water through osmosis, causing it to shrink and decrease in mass. The bags with lower initial concentrations of sucrose would have less water loss and therefore show smaller percent changes in mass over time.

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32.

Endocytosis moves materials ________ a cell via ________.
- Into; facilitated diffusion
- Into; membranous vesicles
- Into; a transport protein
- Out of; diffusion
- Out of; membranous vesicles
Correct Answer

A. Into; membranous vesicles

Explanation

Endocytosis is a process where materials are taken into a cell by forming membranous vesicles. These vesicles are formed by the invagination of the cell membrane, enclosing the material to be transported. Therefore, the correct answer is "into; membranous vesicles".

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33.

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
- Spread in a continuous layer over the inner and outer surfaces of the membrane.
- Confined to the hydrophobic core of the membrane.
- Embedded in a lipid bilayer.
- Randomly oriented in the membrane, with no fixed inside-outside polarity.
- Free to depart from the fluid membrane and dissolve in the surrounding solution.
Correct Answer

A. Embedded in a lipid bilayer.

Explanation

According to the fluid mosaic model of membrane structure, proteins are embedded in a lipid bilayer. This means that proteins are not just spread over the inner and outer surfaces of the membrane, confined to the hydrophobic core of the membrane, randomly oriented in the membrane, or free to depart from the fluid membrane. Instead, they are integrated within the lipid bilayer, with parts of the protein molecule interacting with the hydrophobic tails of the lipids. This arrangement allows for a dynamic and fluid membrane structure where proteins can move laterally within the lipid bilayer.

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34.

Which of the following is correct about integral membrane proteins?
- They lack tertiary structure.
- They are loosely bound to the surface of the bilayer.
- They are usually transmembrane proteins.
- They are not mobile within the bilayer.
- They serve only a structural role in membranes.
Correct Answer

A. 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.

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35.

In a hypotonic solution an animal cell will
- Lyse.
- Experience turgor.
- Neither gain nor lose water.
- Shrivel.
- Lose water.
Correct Answer

A. Lyse.

Explanation

In a hypotonic solution, the concentration of solutes outside the cell is lower than inside the cell. This creates a concentration gradient that causes water to move into the cell through osmosis. As a result, the cell swells and may burst or lyse due to the excess water entering the cell. Therefore, the correct answer is "lyse."

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36.

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 integral membrane proteins are not strong enough to hold the bilayer together.
- Water that is present in the middle of the bilayer freezes and is easily fractured.
- Hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing.
- The carbon-carbon bonds of the phospholipid tails are easily broken.
- The hydrophobic interactions that hold the membrane together are weakest at this point.
Correct Answer

A. 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.

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37.

Of the following functions, which is most important for the glycoproteins and glycolipids of animal cell membranes?
- Facilitated diffusion of molecules down their concentration gradients
- Active transport of molecules against their concentration gradients
- Maintaining the integrity of a fluid mosaic membrane
- Maintaining membrane fluidity at low temperatures
- A cell's ability to distinguish one type of neighboring cell from another
Correct Answer

A. A cell's ability to distinguish one type of neighboring cell from another
38.

Cholesterol enters cells via
- Phagocytosis.
- Osmosis.
- Receptor-mediated endocytosis.
- Exocytosis.
- Pinocytosis.
Correct Answer

A. Receptor-mediated endocytosis.

Explanation

Cholesterol enters cells via receptor-mediated endocytosis. This process involves the binding of cholesterol to specific receptors on the cell surface, which triggers the formation of a vesicle that engulfs the cholesterol molecule. The vesicle then fuses with the cell's internal compartments, allowing the cholesterol to be transported into the cell. This mechanism ensures that cholesterol is selectively taken up by cells and is essential for maintaining cholesterol homeostasis in the body.

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39.

Which of the following processes includes all others?
- Osmosis
- Diffusion of a solute across a membrane
- Facilitated diffusion
- Passive transport
- Transport of an ion down its electrochemical gradient
Correct Answer

A. Passive transport

Explanation

Passive transport is the correct answer because it is a broad term that encompasses all the other processes mentioned. Osmosis, diffusion of a solute across a membrane, facilitated diffusion, and transport of an ion down its electrochemical gradient are all types of passive transport. Passive transport refers to the movement of molecules or ions across a membrane without the need for energy input. Therefore, passive transport includes all the other processes mentioned as they are all examples of passive movement of substances across a membrane.

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40.

The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half filled with a solution of 2 M sucrose and 1 M glucose. Side B is half filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal. Initially, in terms of tonicity, the solution in side A with respect to that in side B is
- Hypotonic.
- Plasmolyzed.
- Isotonic.
- Saturated.
- Hypertonic.
Correct Answer

A. Isotonic.

Explanation

The solution in side A is isotonic to the solution in side B because the initial liquid levels on both sides are equal. Isotonic solutions have the same concentration of solutes, so there is no net movement of water across the membrane.

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41.

What membrane-surface molecules are thought to be most important as cells recognize each other?
- Phospholipids
- Integral proteins
- Peripheral proteins
- Cholesterol
- Glycoproteins
Correct Answer

A. Glycoproteins

Explanation

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.

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42.

All of the following are functions of integral membrane proteins except
- Protein synthesis.
- Active transport.
- Hormone reception.
- Cell adhesion.
- 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.

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43.

Which of the following characterizes the sodium-potassium pump?
- Sodium ions are pumped out of a cell against their gradient.
- Potassium ions are pumped into a cell against their gradient.
- The pump protein undergoes a conformational change.
- Sodium ions are pumped out of a cell against their gradient and potassium ions are pumped into a cell against their gradient.
- 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

A. 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.

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44.

Which of the following adheres to the extracellular surface of animal cell plasma membranes?
- Fibers of the extracellular matrix
- Fibers of the cytoskeleton
- The phospholipid bilayer
- Cholesterol
- Carrier proteins
Correct Answer

A. Fibers of the extracellular matrix

Explanation

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.

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45.

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?
- It will have no unfavorable effect as long as the water is free of viruses and bacteria.
- The patient's red blood cells will shrivel up because the blood fluid is hypotonic compared to the cells.
- The patient's red blood cells will swell because the blood fluid is hypotonic compared to the cells.
- The patient's red blood cells will shrivel up because the blood fluid is hypertonic compared to the cells.
- The patient's red blood cells will burst because the blood fluid is hypertonic compared to the cells.
Correct Answer

A. 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.

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1
46.

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
- It is a peripheral membrane protein.
- It exhibits a specificity for a particular type of molecule.
- It requires the expenditure of cellular energy to function.
- It works against diffusion.
- It has few, if any, hydrophobic amino acids.
Correct Answer

A. 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.

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47.

Which of the following statements about membrane structure and function is false?
- Diffusion of gases is faster in air than across membranes.
- Diffusion, osmosis, and facilitated diffusion do not require any direct energy input from the cell.
- 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.
- Voltage across the membrane depends on an unequal distribution of ions across the plasma membrane.
- Special membrane proteins can cotransport two solutes by coupling diffusion down a concentration gradient to transport against the concentration gradient.
Correct Answer

A. 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.

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48.

Carrier molecules in the membrane and metabolic energy are required for
- Osmosis.
- Facilitated diffusion.
- Active transport.
- Facilitated diffusion and active transport.
- Facilitated diffusion, active transport, and osmosis.
Correct Answer

A. 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.

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49.

Ions diffuse across membranes down their
- Chemical gradients.
- Concentration gradients.
- Electrical gradients.
- Electrochemical gradients.
- Concentration gradients and chemical gradients.
Correct Answer

A. 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.

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Chapter 7 Test - AP Biology

Which of the following statements is correct about diffusion?

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