Chapter 7 Test - AP Biology

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.

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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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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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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.

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.

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.

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.

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.

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.

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.

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.

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".

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.

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.

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.

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.

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.

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."

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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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.