AP Bio Chapter 2 AP Questions

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 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.

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.

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.