Chapter 7: Membrane Structure and Function

Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.

1. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. 2. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. 3. The diverse proteins found in and attached to membranes perform many important functions.

Which of the following statements about the conditions shown in the U-shaped tube are true?

1. There is less free water in the right arm of the tube than in the left arm of the tube. 2. Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane.

Which statement is correct?

The cytoplasm of a red blood cell is hypertonic to a solution of pure water.

If the pores in the selectively permeable membrane became larger, but still not large enough to let the sugar pass through, what would happen during osmosis in the U-shaped tube compared to what is shown in the figure?

The final water levels would be the same as shown in the figure, but the solutions would reach near equal concentrations faster.

How do membrane phospholipids interact with water?

The polar heads interact with water; the nonpolar tails do not.

You are working on a team that is designing a new drug. The drug molecule is large and polar. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?

The presence of a transport protein that allows the drug to pass

Which of the following statements about osmosis is correct?

The presence of aquaporins (proteins that form water channels in the membrane) speeds up the process of osmosis.

If more sugar were added to the solution on the left side of the tube, what would happen to the water level on the right side of the tube?

The water level would go down.

Which of the following statements describes the role of the transport protein in facilitated diffusion?

Transport proteins allow solutes to move passively down their concentration gradients across the membrane.

What happens when two solutions separated by a selectively permeable membrane reach osmotic equilibrium?

Water molecules move between the two solutions, but there is no net movement of water across the membrane.

Which of the following molecular movements is due to diffusion or osmosis?

When a plant cell is placed in concentrated salt water, water moves out of the cell.

In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function.

a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell

If the concentration of phosphate in the cytosol is 2.0 mM, and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol?

active transport

Active and passive transport of solutes across a membrane typically differ in which of the following ways?

active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy

Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. When is this true: Orange die moves independently of purple dye.

always

Are the following true for only channels, only carriers, or both channels and carriers? 1. Transport solutes down a concentration or electrochemical gradient. 2. Are integral membrane proteins. 3. Provide a hydrophilic path across the membrane.

both channels and carriers

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into the following solution. Indicate whether crenation, hemolysis, or neither will occur: Solution A: 3.21% (m/v) NaCl

crenation

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into the following solution. Indicate whether crenation, hemolysis, or neither will occur: Solution D: 6.97% (m/v) glucose

crenation

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into the following solution. Indicate whether crenation, hemolysis, or neither will occur: Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl

crenation

During osmosis, water diffuses across a selectively permeable membrane from the region of higher ____ concentration and lower ____ concentration to the side with lower ____ concentration and higher ____ concentration.

free water, solute, free water, solute

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into the following solution. Indicate whether crenation, hemolysis, or neither will occur: Solution B: 1.65% (m/v) glucose

hemolysis

A red blood cell placed in a hypertonic solution will shrink in a process called crenation. A red blood cell placed in a hypotonic solution will swell and potentially burst in a process called hemolysis. To prevent crenation or hemolysis, a cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution inside the cell, which contains several different solutes. A red blood cell is placed into the following solution. Indicate whether crenation, hemolysis, or neither will occur: Solution C: distilled H2O

hemolysis

Endocytosis moves materials _____ a cell via _____.

into, membranous vesicles

Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. When is this true: Purple dye moves only from side B to side A.

never

Hydrophobic substances like salad oil are

nonpolar molecules that do not have an affinity for water molecules

Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. When is this true: There is no net movement of purple dye.

only at equilibrium

Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. When is this true: Concentration gradients exist that drive diffusion of both dyes.

only before equilibrium is reached

Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. When is this true: There is a net movement of orange dye from side A to side B.

only before equilibrium is reached

Are the following true for only channels, only carriers, or both channels and carriers? 1. Undergo a change in shape to transport solutes across the membrane. 2. Transport primarily small polar organic molecules.

only carriers

Are the following true for only channels, only carriers, or both channels and carriers? 1. Allow water molecules and small ions to flow quickly across the membrane. 2. Provide a continuous path across the membrane.

only channels

A white blood cell engulfing a bacterium is an example of _____.

phagocytosis

A semipermeable membrane is placed between the following solutions: Solution A-1.4% (m/v) starch and Solution B-7.62% (m/v) starch. Which solution will decrease in volume?

solution A

A semipermeable membrane is placed between the following solutions: Solution C-9% (m/v) NaCl and Solution D-12.4% (m/v) NaCl. Which solution will increase in volume?

solution D

You can recognize the process of pinocytosis when _____.

the cell is engulfing extracellular fluid

The permeability of a biological membrane to a specific polar solute may depend on which of the following?

the types of transport proteins in the membrane

Which of the following best describes the structure of a biological membrane?

two layers of phospholipids, with proteins either crossing the layers or on the surface of the layers

Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism?

water, lipids, carbon dioxide, and oxygen