AP Bio Chapter 2 AP Questions
Aldosterone (a steroid hormone) is a small, nonpolar, hydrophobic molecule that enters a target cell by moving across the plasma membrane, down a concentration gradient. Based on the information presented, how does aldosterone most likely enter target cells? A By simple diffusion B By facilitated diffusion C By active transport D By endocytosis
Answer A Correct. Small, nonpolar, hydrophobic molecules can enter a cell by moving across the plasma membrane and down a concentration gradient by simple diffusion.
Some cells, such as intestinal cells, exchange a lot of material with their surroundings. The surface-to-volume ratio of these cells affects the efficiency of material exchange. The table provides measurements of four different eukaryotic cells. Cell 1 2 3 4 Total surface area (μm2) 40 60 80 100 Total volume (μm3) 20 10 30 20 Based on the data, which cell is likely to be most effective in the exchange of materials? A Cell 1 B Cell 2 C Cell 3 D Cell 4
Answer B Correct. The surface area to volume calculation is 6010=6. Of the four cells, this one has the highest ratio of surface area to volume and is likely to be most effective in the exchange of materials.
Gaucher disease is an inherited disorder in which cells of the body are unable to break down a particular type of lipid, resulting in a buildup of the lipid in some tissues and organs. Based on the information provided, Gaucher disease results most directly from a defect in the function of which of the following organelles? A The smooth endoplasmic reticulum B The nucleus C The lysosome D The mitochondrion
Answer C Correct. The lysosome contains specific enzymes used to break down a variety of molecules and cellular waste products. A defect in the function of the lysosomal enzymes that are needed to break down lipids is the most direct cause of Gaucher disease.
A scientist is studying the various prokaryotic and eukaryotic species found floating in a sample of water taken from a marine ecosystem. Which cellular component will be found in the widest range of organisms in the sample? A The chloroplast, since all organisms need a source of energy. B The ribosome, since all organisms need to synthesize proteins. C The mitochondrion, since all organisms need to break down glucose. D The cell wall, since all marine organisms need them for support.
Answer B Correct. Ribosomes are found in all forms of life, allowing for comparison of the widest possible range of plankton species.
Researchers investigate the transport of a certain protein into cells by endocytosis. In an experiment, the researchers incubate the cells in the presence of the protein and measure the amount of the protein that is absorbed into the cells over a five-minute period. Based on their observations, what should the researchers do to further clarify how the availability of the protein outside the cells affects the rate of endocytosis of the protein? A Incubate the cells in the absence of the protein. B Incubate the cells in the presence of several different proteins. C Incubate the cells in the presence of several different concentrations of the protein. D Incubate the cells in the presence of the protein for several different lengths of time.
Answer C Correct. Changing the concentration of the protein will change the availability of the protein outside the cells.
Some viral infections can lead to the rupture of the lysosome membrane. Which prediction of the effect of this disruption of cellular compartmentalization is most likely correct? A Enzymes will be released that will specifically target the virus. B Cellular osmotic concentrations will change, preventing viral entry into the cell. C Hydrolytic enzymes will be released, which will cause cell death. D Intracellular digestion of organic materials will increase, which will increase the energy available to the cell for fighting the virus.
Answer C Correct. Hydrolytic enzymes will be released, resulting in cell death and preventing further viral reproduction.
A magnesium sulfate solution taken orally can cause a net movement of water into the large intestine, which results from water molecules diffusing through aquaporins embedded in the cells of the intestinal lining. By which of the following mechanisms do the water molecules most likely move into the large intestine? A By passive transport from an area of low osmolarity to an area of high osmolarity B By passive transport from an area of high osmolarity to an area of low osmolarity C By active transport from an area of low osmolarity to an area of high osmolarity D By active transport from an area of high osmolarity to an area of low osmolarity
Answer A Correct. Based on the information presented, the water molecules move through aquaporins by diffusing from an area of low osmolarity to an area of high osmolarity, which is an example of passive transport.
Which of the following observations best supports the claim that mitochondria evolved from once-free-living prokaryotic cells by the process of endocytosis? A Mitochondria produce ATP. B Mitochondria contain proteins. C Mitochondria exchange substances with the cytosol. D Mitochondria are surrounded by a double membrane.
Answer D Correct. The double membranes of mitochondria provide evidence that an ancestor of mitochondria, which was most likely a type of free-living aerobic bacterium, was ingested via endocystosis by a primitive eukaryotic cell.
Lysosomes digest food particles brought into a cell by endocytosis. After a vesicle containing food particles fuses with a lysosome, H+ ions are transported into the lysosome from the cytosol. This significantly lowers the pH of the lysosome relative to the cytosol and activates the enzymes that digest the particles. Which of the following best predicts what will happen to the lysosomal enzymes if the proteins that transport H+ ions from the cytosol into the lysosome are damaged? A The lysosomal enzymes will not become active, since there will be no active transport of H+ ions. B The lysosomal enzymes will not become active, since H+ ions will diffuse out of the lysosome. C The lysosomal enzymes will become active, since facilitated diffusion will move H+ ions into the lysosome. D The lysosomal enzymes will become active, since passive diffusion will move H+ ions into the lysosome.
Answer A Correct. Since the pH of the lysosome has to become lower than that of the cytosol, active transport is needed to move H+ ions into the lysosome, against the H+ ion concentration gradient, to activate the enzymes.
Figure 1. Testosterone movement across the cellular membrane The figure presents a cellular membrane bilayer. A point between two lipid molecules on the outer surface of the membrane is labeled 1. A protein associated only with the outer surface membrane is labeled 2. A channel protein embedded in the membrane is labeled 3. A solid appearing protein with an extracellular chain of sugars is embedded in the membrane and is labeled 4. Testosterone is a small steroid hormone that is important in cell signaling. Which of the following indicates where testosterone enters a cell and why it is able to cross at that point? A 1, because testosterone is nonpolar and can diffuse through the membrane. B 2, because testosterone covalently binds to a surface protein and transports into the cell. C 3, because testosterone dissolves in water and flows through the channel. D 4, because testosterone is filtered out of the extracellular fluid and taken into the cell by endocytosis.
Answer A Correct. Steroids such as testosterone are hydrophobic lipids. Therefore, testosterone can cross the hydrophobic inner region of the phospholipid bilayer.
Intravenous (IV) therapy is used for fluid replacement in instances of dehydration in humans and other animals. One type of IV fluid is essentially a saltwater solution. To determine the best concentration for therapy in people, a team of students is researching the effects of solutions of different salt concentrations on red blood cells. The following observations were made from three different red blood cell samples viewed under a microscope. The figure presents three blood cells. The left cell is swollen, the middle cell is of normal disc shape, and the right cell is shrunken and irregular. 0.3% Saline (Cells swell) 0.9% Saline (Cells unchanged) 1.5% Saline (Cells shrink) The team wants to extend the research project. What should the team of students do next to obtain data that are more conclusive? A Repeat the process with other salt concentrations. B Develop a model to explain why the cells react differently to different salt concentrations. C Repeat the process using red blood cells from other animals. D Develop an experimental procedure that uses a stain that makes the organelles of red blood cells more visible.
Answer A Correct. The figures illustrate the extremes of hypotonic (swollen cells) and hypertonic (shriveled cells) environments, so an extension would be to investigate the small range of acceptable salt concentrations in IV fluid solutions.
Stomata are pores on the surfaces of the leaves and stems of plants that regulate gas exchange between the plants and the atmosphere. Researchers found that the stomata density on the leaves of a species of plant change as the concentration of CO2 in the atmosphere changes. When grown at 350 ppm CO2 the plant has an average density of 300 stomata per mm2, but when grown at 400 ppm CO2 the plant has an average density of 250 stomata per mm2. Which of the following best describes how the ratio of the density of stomata (stomata per mm2) per CO2 concentration (ppm CO2) changes as the CO2 concentration increases? A The ratio decreases from 0.86 to 0.63, because fewer stomata are needed at higher CO2 concentrations. B The ratio decreases from 1.6 to 1.2, because fewer stomata are needed at higher CO2 concentrations. C The ratio increases from 0.63 to 0.86, because more stomata are needed at higher CO2 concentrations. D The ratio increases from 1.2 to 1.6, because more stomata are needed at higher CO2 concentrations.
Answer A Correct. The ratio of 300 stomata per mm2 to 350 ppm CO2 is 0.86, and the ratio of 250 stomata per mm2 to 400 ppm CO2 is 0.63. This reflects that fewer stomata are needed as the concentration of CO2 increases.
The figure shows a representation of a protein embedded in a cell membrane. The numbers indicate different structural regions of the protein. The figure presents a cell membrane lipid bilayer. A protein is embedded in one half of the bilayer. The exposed surface of the protein that protrudes from the membrane is labeled 1, and the part of the protein that associates with the fatty acid tails in the interior of the membrane is labeled 2. Based on the figure, which of the following statements best describes the relationship between regions 1 and 2 of the protein? A Region 1 is hydrophilic because it interacts with the interior of the membrane, whereas region 2 is hydrophobic because it interacts with an aqueous environment. B Region 1 is hydrophilic because it interacts with an aqueous environment, whereas region 2 is hydrophobic because it interacts with the interior of the membrane. C Region 1 is hydrophobic because it interacts with the interior of the membrane, whereas region 2 is hydrophilic because it interacts with an aqueous environment. D Region 1 is hydrophobic because it interacts with an aqueous environment, whereas region 2 is hydrophilic because it interacts with the interior of the membrane.
Answer B Correct. A cell membrane is a phospholipid bilayer that separates one aqueous environment from another. The interior of a phospholipid bilayer is a hydrophobic environment. Because region 1 interacts with the aqueous environment on one side of the phospholipid bilayer, it is most likely hydrophilic. Because region 2 interacts with the interior of the phospholipid bilayer, it is most likely hydrophobic.
A study was conducted to understand the factors controlling the rate at which molecules or ions travel across cell membranes. An artificial membrane was created that was composed of a phospholipid bilayer only. The speed at which various substances crossed this membrane was measured. Some substances can pass through an actual cell membrane much faster than they passed through the artificial membrane in this study. Which of the following statements best explains this finding? A Actual cell membranes have a much thicker phospholipid bilayer than the artificial membrane does. B Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane. C Hydrophobic substances spend more time between the two layers of phospholipid in the artificial membrane than they do between the layers in an actual membrane. D Hydrophilic substances spend more time attached to the polar region of the phospholipids in the artificial membrane than they do attached to the polar region of the phospholipids in an actual membrane.
Answer B Correct. Actual cell membranes have a variety of embedded proteins that increase the movement of substances across the membrane by both active and passive transport.
In an experiment, researchers provided a radiolabeled amino acid to living plant cells. After one hour, the researchers determined the amount of the radiolabeled amino acid that was in each of several subcellular compartments. The results of the experiment are represented in the table. RELATIVE AMOUNTS OF RADIOLABELED AMINO ACID Nucleus Mitochondria Endoplasmic Reticulum Cytosol 2.1 2.7 1.9 1 Which of the following conclusions about the radiolabeled amino acid is best supported by the results of the experiment? A It was mostly incorporated into nucleic acids that store the biological information. B It was mostly incorporated into proteins that regulate and manage metabolic reactions. C It was mostly incorporated into lipids that help separate cells from their surrounding environment. D It was mostly incorporated into carbohydrates that form protective structures outside the cells.
Answer B Correct. Amino acids are the building block of proteins, and the data indicate that most of the radiolabeled amino acid was in the mitochondria. Therefore, the data best support the conclusion that most of the amino acid molecules were incorporated into proteins that regulate and manage the metabolic reactions that occur in mitochondria.
Beetroot cells contain a family of dark red pigments called betalains. The selectively permeable nature of the beetroot cells keeps the internal environment of the cell separate from the external environment of the cell. Researchers are interested in determining whether the selective permeability of beetroot cells is due to the cell membrane or if it is due to the cell wall. Exposure to cellulase is known to damage the structure of the cell wall. An experiment is set up in which beetroot cells are placed in an aqueous solution with cellulase and in one without cellulase. Which of the following results best refutes the alternative hypothesis that selective permeability is a consequence of the cell wall? A When beetroot cells are placed in a solution with cellulase, the solution turns dark red. B When beetroot cells are placed in a solution with cellulase, the solution remains clear. C When beetroot cells are placed in a solution, it turns dark red with or without cellulase present. D Since plant cells contain cell membranes, not cell walls, the alternate hypothesis cannot be tested.
Answer B Correct. Cellulase digests cellulose and damages the structure of the cell wall, not the cell membrane. The lack of color change in the solution indicates that the betalain is not leaking out of the beetroot cells even though the cell wall has been damaged. This refutes the alternative hypothesis.
In an experiment, researchers compared the growth of two different plants, plant X and plant Y. The researchers maintained the plants under nearly identical conditions and observed that plant X grew faster than plant Y. The researchers also observed that the inner mitochondrial membranes of plant X had more folds than did those of plant Y. Which of the following conclusions about increasing the number of folds in the inner mitochondrial membrane is best supported by the results of the experiment? A It increases the efficiency of photosynthesis, which results in faster cell growth. B It increases the surface area available for ATP production, which results in faster cell growth. C It increases the amount of space available for storing cellular wastes, which results in faster cell growth. D It increases the rate of protein transport to the plasma membrane, which results in faster cell growth.
Answer B Correct. The increased surface area of the folds will contain more ATP synthase, allowing for more efficient use of the chemiosmotic gradient and more efficient production of ATP. The observation that plant X grew faster than plant Y supports this conclusion.
Some membrane proteins help maintain the concentrations of ions inside a cell by transporting the ions across the cell's plasma membrane. Other membrane proteins form pores in the plasma membrane through which the ions can diffuse. A model showing the influence of membrane proteins on the movement of sodium (Na+) and potassium (K+) ions across a plasma membrane is presented in Figure 1. The figure presents a bilayer plasma membrane, which separates the cytosol from the extracellular region. In the cytosol, the concentration of N a plus is low, and the concentration of K plus is high. In the extracellular region, the concentration of N a plus is high, and the concentration of K plus is low. Three membrane proteins are embedded in the plasma membrane. One protein has a channel, through which N a plus leaks into the cytolsol from the extracellular region. Another protein has a channel, through which K plus leaks out from the cytosol into the extracellular region. A third protein is a pump protein, through which Na plus is pumped out from the cytosol to the extracellular region and K plus is pumped into the cytosol from the extracellular region. Figure 1. Section of a cell's plasma membrane, showing ion concentrations and membrane proteins Based on the model presented in Figure 1, which of the following changes will most likely result from a depletion of available ATP stores inside the cell? A The Na+ concentration outside the cell will increase. B The Na+concentration inside the cell will increase. C The K+ concentration inside the cell will increase. D The K+ concentration outside the cell will decrease.
Answer B Correct. Without ATP, the Na+ ions will continue to leak into the cell but will not be pumped out of the cell, resulting in a concentration increase inside the cell.
Figure 1 presents a dialysis bag immersed in a beaker of water. Figure 1 A student is using dialysis bags to model the effects of changing solute concentrations on cells. The student places one dialysis bag that contains 25 mL of distilled water into each of two beakers that are filled with 200 mL of distilled water. (Figure 1). The membrane of each dialysis bag membrane contains pores that allow small solutes such as monoatomic ions to pass through but are too small for anything larger to pass. After 30 minutes, 5 mL of a concentrated solution of albumin (a medium-sized, water-soluble protein) is added to one of the two beakers. Nothing is added to the other beaker. After two more hours at room temperature, the mass of each bag is determined. There is no change in the mass of the dialysis bag in the beaker to which no albumin was added. Which of the graphs below best represents the predicted change in mass over time of the dialysis bag in the beaker to which albumin was added? A The figure presents a graph in the coordinate plane. The horizontal axis is labeled Time, in minutes, and the numbers 0 through 150, in increments of 30, are indicated. The vertical axis is labeled Relative Mass of Dialysis Bag. The axis has an arrowhead at the top end, and no numbers are indicated along it. The graphed line begins at 0 minutes, about halfway up the vertical axis, and extends horizontally to the right until it ends at 150 minutes. A label indicates Albumin Added at 30 minutes. B The figure presents a graph in the coordinate plane. The horizontal axis is labeled Time, in minutes, and the numbers 0 through 150, in increments of 30, are indicated. The vertical axis is labeled Relative Mass of Dialysis Bag. The axis has an arrowhead at the top end, and no numbers are indicated along it. The graphed line begins at 0 minutes, about halfway up the vertical axis, and extends horizontally to the right until 30 minutes. A label indicates Albumin Added at 30 minutes. The graphed line starts to move downward and to the right at 30 minutes until it ends at 150 minutes, just above the horizontal axis. C The figure presents a graph in the coordinate plane. The horizontal axis is labeled Time, in minutes, and the numbers 0 through 150, in increments of 30, are indicated. The vertical axis is labeled Relative Mass of Dialysis Bag. The axis has an arrowhead at the top end, and no numbers are indicated along it. The graphed line begins at 0 minutes, about one third of the way up the vertical axis, and moves upward and to the right until it is about halfway up the vertical axis at 30 minutes. A label indicates Albumin Added at 30 minutes. The graphed line then moves downward and to the right until it ends at 150 minutes, about one third of the way up the vertical axis. D The figure presents a graph in the coordinate plane. The horizontal axis is labeled Time, in minutes, and the numbers 0 through 150, in increments of 30, are indicated. The vertical axis is labeled Relative Mass of Dialysis Bag. The axis has an arrowhead at the top end, and no numbers are indicated along it. The graphed line begins at 0 minutes, about halfway up the vertical axis, and extends horizontally to the right until 30 minutes. A label indicates Albumin Added at 30 minutes. The graphed line then moves upward and to the right until it ends at 150 minutes, near the top of the vertical axis.
Answer B Correct: The graph indicates no change in the mass of the dialysis bag for the first 30 minutes in an isotonic environment and then shows a decrease in mass when the environment became hypertonic with the addition of albumin.
The cell membrane is selectively permeable due to its structure. Thus, the internal environment of the cell is distinct from the external environment of the cell. One biologist hypothesizes that small nonpolar molecules readily pass through the membrane. Another biologist alternatively hypothesizes that these types of molecules require channel and transport proteins that are embedded in the membrane in order to move across the membrane. Which of the following data would best refute this alternative hypothesis? A Ethanol is found in the cytosol of cells when they are briefly exposed to a ten percent ethanol solution. B Cells become oxygen deficient when membrane protein activity is blocked. C CO2 and N2 movement in and out of cells is unaffected when membrane protein activity is blocked. D Sodium ions cannot move across the cell membrane when membrane protein activity is blocked.
Answer C Correct. Both CO2 and N2 are small nonpolar molecules. Their ability to enter and leave cells normally when membrane protein activity is blocked would refute the alternative hypothesis.
Which of the following transport mechanisms will be affected most directly by a temporary shortage of ATP molecules inside the cell? A The movement of water molecules through aquaporins B The diffusion of oxygen molecules across the plasma membrane C The transport of glucose molecules against a concentration gradient D The facilitated diffusion of Ca2+ ions into the cell
Answer C Correct. The active transport of glucose molecules against a concentration gradient requires an input of energy. Biological processes that require an input of energy typically incorporate the hydrolysis of ATP, an energy-rich molecule.
Hereditary spherocytosis (HS) is a disorder of red blood cells that causes the cells to be smaller and spherical instead of having the usual flattened, biconcave shape. The average diameter of normal red blood cells is 7.2μm, and the average diameter of red blood cells in a person with HS was found to be 6.7μm. The normal red blood cell has an average surface area of 136μm2 and an average volume of 91μm3. Which of the following provides an accurate calculation of the surface area to volume ratio of an HS red blood cell, as well as a prediction of its effect on the efficient transferring of oxygen compared to a normal red blood cell? A The ratio is 0.45, and the cells are more efficient at transferring oxygen. B The ratio is 1.12, and the cells are less efficient at transferring oxygen. C The ratio is 0.89, and the cells are less efficient at transferring oxygen. D The ratio is 141, and the cells are more efficient at transferring oxygen.
Answer C Correct. The correct calculation of the surface area to volume ratio of the HS cell is 0.89. This ratio is less than the ratio found in a normal red blood cell, 1.49, so the cell would be less efficient at transferring oxygen.
Certain bacteria can use both ethyl alcohol and acetate as sources of nutrients. In an experiment where both nutrients are available to a bacterial population, the following results were obtained and graphed. The figure presents two curves in the first quadrant of a coordinate plane, titled "Movement of Nutrients into Bacterial Cells." The horizontal axis is labeled Concentration Outside Cells, in milimolarity, and the numbers 0.1, 1.0, 10.0, and 100.0 are indicated at equal intervals. The vertical axis is labeled Rate of Entry of Substance, in micromoles per minute, and the numbers 10, 100, and 1,000 are indicated at equal intervals. The first curve, labeled Acetate, is a straight line that begins at the point 0.1 milimolar, 1.5 micromoles per minute, and moves upward and to the right, passing through the point 1.0 milimolar, 10.4 micromoles per minute. The curve then passes through the point 10.0 milimolars, 107 micromoles per minute, and ends at the point 100.0 milimolars, 1,020 micromoles per minute. The second curve, labeled Ethyl Alcohol, begins at the point 0.1 millimolar, 7 micromoles per minute, and moves gradually upward and to the right, passing through the point 1.0 millimolar, 20 micromoles per minute. It then passes through the point 10.0 millimolar, 35 micromoles per minute, and ends at the point 100.0 milimolar, 50 micromoles per minute. What additional procedure would best help determine whether these movements are due to active transport or to passive transport? A Repeat the original experiment, but at three different temperatures. Compare the transport rates among the three temperatures. B Repeat the original experiment, but add a substance known to block movement of molecules across aquaporins. Compare the rates on the two graphs. C Use two additional treatments, one containing only ethyl alcohol and one containing only acetate. Compare the graphs of these two treatments with the original graph. D Use two additional treatments, one containing only ethyl alcohol and one containing only acetate. Include a substance known to block ATP use by the plasma membrane. Compare the graphs of these two treatments to the original graph.
Answer D Correct. Active transport requires the availability of ATP. If the nutrients are actively transported, blocking ATP use should reduce the rate of transport along the whole concentration range. If these two graphs are the same as the original graph, the transport is passive. Separation of the nutrients eliminates the possibility that the two transport processes could interfere with each other.
Researchers have proposed a model of chloroplast evolution. According to the model, chloroplasts evolved from a small prokaryotic organism that was engulfed by an ancestral eukaryote. The engulfed prokaryote then formed an endosymbiotic relationship with the eukaryotic host. Which of the following observations best supports the model? A Chloroplasts are separated from other subcellular compartments by semipermeable membranes. B Prokaryotic and eukaryotic organisms both acquire nutrients from the surrounding environment. C Eukaryotes evolved after prokaryotes and have more complex structures. D Chloroplasts and some prokaryotes share similar photosynthetic reactions.
Answer D Correct. Photosynthesis is a feature of only a limited number of organisms, including cyanobacteria, algae, and plants. The fact that this specialized process is similar in prokaryotes, such as cyanobacteria, and in eukaryotes, such as algae and plants, provides evidence in support of the model.
A certain type of specialized cell contains an unusually large amount of rough endoplasmic reticulum (ER). Which of the following functions is this cell type most likely specialized to perform? A The production and secretion of steroids B The destruction of toxic materials produced in other cells of the organism C The synthesis of polysaccharides for energy storage D The production and secretion of proteins
Answer D Correct. The cytosolic surface of the rough ER is covered by ribosomes that synthesize proteins that are then transported into the rough ER, then to the Golgi complex, and finally out of the cell.
Researchers conducted an experiment to investigate the effects of a valinomycin treatment on skeletal muscle cells. Valinomycin is a naturally occurring substance that can be used as a drug. The results of the experiment are presented in the table. Relative Rates of ATP Production Time after Treatment Untreated Cells Valinomycin-Treated Cells 5 minutes 1.0 0.3 10 minutes 7.7 2.7 Which of the following claims about the effects of the valinomycin treatment is best supported by the data presented in the table? A The valinomycin treatment caused an increase in the activity of the rough endoplasmic reticulum. B The valinomycin treatment caused an increase in the activity of the Golgi complex. C The valinomycin treatment caused a decrease in the activity of the lysosome. D The valinomycin treatment caused a decrease in the activity of the mitochondria.
Answer D Correct. The data indicate that the valinomycin treatment caused a decrease in the relative rate of ATP production, which likely resulted from impaired mitochondrial function.
A group of mutations, known as MT-ND1, have been identified in mitochondrial DNA. These mutations are associated with a number of debilitating diseases stemming from the production of nonfunctional proteins in the mitochondria. Which of the following cellular deficiencies would most likely be related to these MT-ND1 mutations? A The cell is unable to synthesize most proteins required for normal cell functions. B The cell is unable to break down toxic materials and would accumulate large volumes of these materials. C The cell is able to synthesize proteins, but the proteins would not fold properly and would not contain the correct molecular tags for export from the cell. D The cell is unable to complete reactions related to electron transport and ATP production.
Answer D Correct. The electron transport chain and ATP production are associated with proteins in the inner membrane of the mitochondrion. Nonfunctional proteins in the mitochondrion are likely to result in reduced ATP production.
Two competing hypotheses exist regarding the cell membrane structure. One hypothesis states that membrane structure is static and membrane components throughout the bilayer are rigidly bound. Alternatively, the other hypothesis states that cell membranes are a fluid mosaic in which membrane components may drift within the bilayer around the surface of the cell. An experiment is set up in which membrane proteins of two different cells are fluorescently labeled with two different colors and then fused as shown in Figure 1. The figure presents a model of a cell fusion experiment. There are two cells, and the membranes of each cell have proteins embedded in them. The membrane proteins in one cell are colored grey, and the membrane proteins in the other cell are colored black. The figure shows the grey cell and the black cell beginning to merge. Figure 1. Model of initiation of cell fusion experiment Which of the following results, one hour after membrane fusion, best supports the alternative hypothesis that the cell membrane is a fluid mosaic? A The figure presents a model of a cell. The membrane of the cell has only grey proteins embedded in it. B The figure presents a model of a cell. The membrane of the cell has only black proteins embedded in it. C The figure presents a model of a cell. The membrane of the cell has both grey proteins and black proteins embedded in it. The black proteins are concentrated in one area of the cell membrane, and the grey proteins are concentrated in a separate area of the cell membrane. D The figure presents a model of a cell. The membrane of the cell has both grey proteins and black proteins embedded in it. The grey proteins and black proteins are distributed throughout the cell membrane, and are not concentrated in particular areas.
Answer D Correct. The membrane proteins from each cell have mixed and drifted within the bilayer, which supports the fluid mosaic model of cell membranes. Cell membranes consist of a structural framework of phospholipid molecules that is embedded with proteins and steroids that may flow around the surface of the cell within the bilayer.
Cholesterol is a naturally occurring substance that helps regulate the fluidity of a cell's plasma membrane. A cholesterol molecule can be represented as having a polar head and a nonpolar region, as shown in the figure. The figure presents a cholesterol molecule. A black dot indicates the polar head, which is attached to a nonpolar region that is represented by a sequence of four hexagons or a pentagon, each of which shares one side with the previous and/or next component of the region. Which of the following models shows how cholesterol molecules most likely interact with the phospholipid bilayer of a cell's plasma membrane? A The figure presents a phospholipid bilayer and cholesterol molecules. The polar head of each cholesterol molecule is situated between the heads of the phospholipids, and the nonpolar region extends out and away from the membrane. B The figure presents a phospholipid bilayer and cholesterol molecules. Each cholesterol molecule lies flat against the outer surface of the membrane so that the polar head and nonpolar region of each molecule are both in contact with the phospholipid heads. C The figure presents a phospholipid bilayer and cholesterol molecules. The cholesterol molecules are located in the interior of the membrane and separate the two layers of the bilayer from each other. D The figure presents a phospholipid bilayer and cholesterol molecules. The polar head of each cholesterol molecule is situated between the heads of the phospholipids, and the nonpolar region extends into the interior of the membrane between the phospholipid tails.
Answer D Correct. The model correctly shows the polar heads of the cholesterol molecules interacting with the polar heads of the phospholipids. Also, the model correctly shows the nonpolar regions of the cholesterol molecules interacting with the hydrophobic interior of the phospholipid bilayer.
Euglenids are single-cell eukaryotes that live in aquatic environments. The chloroplasts found inside euglenids are enveloped by three membranes, as represented in Figure 1. The inner membrane of euglenid chloroplasts resembles the thylakoid membrane. The figure presents a Euglenid. A chloroplast is labeled inside the euglenid. There is also an enlarged zoomed-in figure of a portion of the chloroplast. The three membranes of the envelope that surrounds the chloroplast are labeled Chloroplast Envelope, and the innermost membrane of the three is labeled Inner Membrane. The zoom-in also shows a portion of a thylakoid inside the chloroplast itself, and a label points to the thylakoid membrane. Figure 1. Simplified diagram of a euglenid, showing the structure of the chloroplast envelope Which of the following claims about the origin of the euglenid chloroplast is best supported by the three-membrane structure of the envelope? A It originated from the spontaneous assembly of organic molecules into a lipid bilayer inside a free-living prokaryote. B It originated from the fusion of the plasma membranes of two different free-living photosynthetic prokaryotes. C It originated from the incorporation of a photosynthetic prokaryote into a eukaryotic cell by a single endosymbiotic event. D It originated from the incorporation of a photosynthetic prokaryote into a eukaryotic cell by two endosymbiotic events.
Answer D Correct. The three-membrane structure of the chloroplast envelope best supports the claim presented in this answer choice. The three-membrane structure most likely resulted from two endosymbiotic events, with the middle membrane originating from the first event and the outer membrane originating from the second event.