AP Biology : 2.6 Membrane Transport – Exam Style questions with Answer- MCQ

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Question

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/Explanation


Ans: A
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.

Question

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/Explanation

Ans: D
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.

Question

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/Explanation

Ans: C
Changing the concentration of the protein will change the availability of the protein outside the cells.

Question

Figure 1 shows a model of how a channel protein influences the movement of a particle across a cell’s plasma membrane.

The figure shows a section of a cell’s plasma membrane, with a channel protein embedded in the membrane and a concentration gradient across the membrane. Extracellular Space is indicated above the plasma membrane. Intracellular Space, cytosol, is indicated below the plasma membrane. Small hexagons represent a small particle. There are about six times as many hexagons in the extracellular space as in the intracellular space, and two hexagons are shown traversing the channel in the protein.

Figure 1. A section of a cell’s plasma membrane, showing a channel protein and a concentration gradient across the membrane

An investigator wants to understand whether a newly found membrane protein is involved in membrane transport of a certain particle. Which investigation will help determine whether the new membrane protein is a channel protein involved in membrane transport?

A. Add small nonpolar molecules to the extracellular space and measure the direction of particle movement of the molecules.

B. Measure the rate of extracellular fluid movement into the intracellular space.

C. Add more of the proteins to the plasma membrane and measure the rate of the particle movement.

D. Remove ATP from the intracellular space and measure the rate of the particle movement into the intracellular space.

▶️Answer/Explanation

Ans: C
If the movement of particles is mediated by the channel protein, then an increase in proteins in the cell membrane should influence the rate of particle movement across the membrane.

Question

Water is constantly diffusing into the cytosol of freshwater single-celled organisms. In order to maintain the proper solute concentrations in the cytosol, contractile vacuoles pump out the excess water. An experimenter placed single-celled organisms into various saline concentrations and recorded the ATP used by the contractile vacuole. The data are shown in the graph.

The figure presents the graph of a curve in a coordinate plane. The horizontal axis is labeled “Relative Salinity of Environment.” The vertical axis is labeled “Relative Use of A T P by the Contractile Vacuole.” The curve begins close to the top and slightly to the right of the vertical axis. The curve slopes downward and to the right at an incline that gradually becomes less steep as relative salinity of the environment increases. The curve ends a bit above the horizontal axis on the right side of the coordinate plane.
Of the following, which additional investigation can be used to determine when the cells are in an isotonic solution?
A. Decreasing the salinity of the environment a little at a time until the ATP usage reaches a maximum
B. Decreasing the salinity of the environment a little at a time until ATP usage reaches a minimum
C. Increasing the salinity of the environment a little at a time until ATP usage reaches a maximum
D. ncreasing the salinity of the environment a little at a time until the ATP usage reaches a minimum
▶️Answer/Explanation

Ans: D
If the environment is isotonic to the cell, the net flow of water due to diffusion is zero, and ATP is not used to pump water out of the cell.

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