Bio EOY

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. 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?

• The Na+ concentration outside the cell will increase.

• The Na+ concentration inside the cell will increase.

• The K+ concentration inside the cell will increase.

• The K+ concentration inside the cell will decrease.

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?

• Incubate the cells in the absence of the protein.

• Incubate the cells in the presence of several different proteins.

• Incubate the cells in the presence of several different concentrations of the protein.

• Incubate the cells in the presence of the protein for several different lengths of time.

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?

• Actual cell membranes have a much thicker phospholipid bilayer than the artificial membrane does.

• Actual cell membranes have a variety of proteins embedded in the membrane that are absent in the artificial membrane.

• 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.

• 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.

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?

• By passive transport from an area of low osmolarity to an area of high osmolarity

• By passive transport from an area of high osmolarity to an area of low osmolarity

• By active transport from an area of low osmolarity to an area of high osmolarity

• By active transport from an area of high osmolarity to an area of low osmolarity

What will cholesterol do to the fluidity of a plasma membrane when a cell is exposed to cooler conditions.

• Increase in fluidity

• Decrease in fluidity

• No change