Chapter 7
When the system illustrated above reaches equilibrium, the sugar concentrations on both sides of the U-tube will be ________.
1.5 M glucose, 1.5 M glucose
Which of the following statements best describes some aspect of the function of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?
A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.
What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
Amphipathic nature
Which of the following statements is TRUE with regard to this animation?
Both sodium and potassium ions are transported against their concentration gradients. Submit
In what way do the membranes of a eukaryotic cell vary?
Certain proteins are unique to each membrane.
Drag the terms on the left to the appropriate blanks on the right to complete the sentence. Terms may be used more than once.
During osmosis, water diffuses across a selectively permeable membrane from the region of higher free water concentration and lower solute concentration to the side with lower free water concentration and higher solute concentration.
Which of the following statements correctly describes some aspect of exocytosis or endocytosis?
Exocytosis and endocytosis change the surface area of the plasma membrane.
If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?
Hypotonic
Which of the following statements best describes a characteristic feature of osmosis?
In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
Which of the following statements best describes a characteristic feature of a carrier protein in a plasma membrane?
It exhibits specificity for a particular type of molecule.
Which of the following statements best explains why the sodium-potassium pump is an electrogenic pump?
It generates voltage across the membrane.
Which of the following statements best describes a characteristic feature of diffusion?
It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
Which of the following is a major difference between prokaryotic and eukaryotic cells?
Most prokaryotic cells have no internal membranes; eukaryotic cells do.
Which of the following molecules would likely diffuse through the lipid bilayer of a plasma membrane most rapidly?
O2
Select the correct statement about osmosis.
Osmosis is the diffusion of water molecules across a selectively permeable membrane.
Three lab groups carried out an experiment to identify the concentration of sucrose in six solutions. Each unknown solution (1-6) contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and -1.0 M. Cubes of sweet potato (1 cm3) were soaked for 24 hours in each solution and weighed to determine the change in mass. Each data entry represents the average of three sample replicates expressed as percent change in mass following a 24-hour soak in the unknown solutions. From the data given, which statement below most accurately describes something that has occurred in response to a particular unknown solution?
Osmosis of water molecules from unknown solution 2 likely caused the increase in mass observed.
Which of the following particles could diffuse easily through a cell membrane?
Oxygen (O2)
Which of the following statements is true regarding potential energy?
Potential energy is the energy possessed by matter due to its location or structure. Submit
Which of the following statements best explains the observation that proton pumps are used by organisms in every domain of life?
Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
A semipermeable membrane is placed between the following solutions. Which solution will decrease in volume?
Solution A: 1.4% (m/v) starch
A semipermeable membrane is placed between the following solutions. Which solution will increase in volume?
Solution D: 12.4% (m/v) NaCl Submit
Which of the following statements best describes the normal tonicity conditions for typical plant and animal cells in their native environments?
The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution. Submit
Which of the following results is most likely result if a portion of an animal's blood is replaced with distilled water?
The animal's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.
What will happen to a red blood cell (RBC), which has an internal ion content of about 0.9%, if it is placed into a beaker of pure water?
The cell will swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.
Which statement is correct?
The contents of a red blood cell are hyperosmotic to distilled water.
Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.
The diverse proteins found in and attached to membranes perform many important functions. 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. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. Submit
Which of the following statements best describes how unsaturated fatty acids increase membrane fluidity at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
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.
Celery stalks that are immersed in fresh water for several hours become stiff. Which of the following statements best explains the observation that similar stalks left in a 0.15 M salt solution become limp?
The fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
Which of the following statements best describes the structure of a membrane based on the fluid mosaic model?
The membrane is composed of a fluid bilayer of phospholipids with embedded amphipathic proteins.
Which of the following statements best explains how the membranes in winter wheat are able to remain fluid in extremely cold temperatures?
The membranes contain an increased proportion of unsaturated phospholipids. Submit
How do membrane phospholipids interact with water?
The polar heads interact with water; the nonpolar tails do not.
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.
Which of the following statements best describes characteristic activities of a sodium-potassium pump?
The pump moves three sodium ions out of a cell and two potassium ions into a cell using energy from ATP hydrolysis. Submit
Which factors affect the rate of osmotic movement of water?
The rate of osmosis increases with increasing differences in solute concentrations between two solutions separated by a selectively permeable membrane. Submit
What would be observed by live-cell fluorescence microscopy immediately after HIV entry if HIV enters the cell by endocytosis first, and then later fuses with the endocytotic vesicle membrane?
The red fluorescent dye-labeled lipids will appear in the infected cell's interior. Submit
Cell membranes have distinct inside and outside faces. Which of the following statements is the most plausible explanation for the asymmetrical nature of the two layers of the membrane?
The two layers of a cell membrane face different environments and carry out different functions.
Which of the following statements about a typical plasma membrane is correct?
The two sides of the plasma membrane have different lipid and protein composition.
Which of the following is the most likely result when the system has reached equilibrium?
The water level will be higher in side A than in side B.
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 about the conditions shown in the U-shaped tube are true?
There is less free water in the right arm of the tube than in the left arm of the tube. Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane. Submit
When the interior of a cell is in equilibrium with its environment, which of the following statements best describes the relative movement of molecules that can diffuse through the plasma membrane?
There is random movement of molecules into and out of the cell.
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.
True or false? Osmosis is a type of diffusion.
True
True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.
True
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. Submit
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.
The force driving simple diffusion is ________, while the energy source for active transport is ________.
a concentration gradient; ATP hydrolysis Submit
Which of the following factors would tend to increase membrane fluidity?
a greater proportion of unsaturated phospholipids
If you are going to bake potatoes, and your potatoes are soft and dehydrated, they can be soaked in __________ to make them more firm before baking.
a hypotonic solution such as tap water Submit
Which of the following molecules would decrease the electrochemical gradient across a membrane?
a potassium channel
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
In which of the following circumstances would the cell or organism have the greatest need for osmoregulation?
a salmon moving from a river into an ocean
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 Submit
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
A cell that neither gains nor loses water while sitting in a solution is probably sitting in
an isotonic environment.
A defect in which of the following molecules would dramatically reduce the rate of diffusion of water across cell membranes?
aquaporins
An animal cell that lacks carbohydrates on the external surface of its plasma membrane would likely be impaired in which of the following functions?
cell-cell recognition
The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Because phosphate import depends on a pH gradient across the membrane, phosphate transport is most likely an example of which of the following transport processes?
cotransport
The movement of glucose into a cell against its concentration gradient is most likely to be accomplished by which of the following?
cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis
In some cells, there are many different ion electrochemical gradients across the plasma membrane even though there are usually only one or two types of proton pumps present in the membrane. The gradients of the other ions are most likely established by which of the following?
cotransport proteins
Which of the following is least likely to be important in holding the components of a biological membrane together?
covalent interactions between the phospholipid and protein components of the membrane
Based on the figure above, which of these experimental treatments would increase the rate of sucrose transport into a plant cell?
decreasing extracellular
Which of the following factors is a primary contributor underlying cause of familial hypercholesterolemia?
defective LDL receptors on the cell membranes
According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
embedded in a lipid bilayer.
Paramecium is a genus of protists that lives in water. It has organelles called contractile vacuoles that continually eliminate the excess water gained through osmosis. Knowing that Paramecia gain water through osmosis, we can deduce that they normally live in
freshwater lakes and ponds.
Identify Structure A.
glycoprotein
Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to diarrhea. Today these diseases are usually not fatal because of the development of which of the following types of treatments?
hydrating drinks with high concentrations of salt and glucose
This cell is in a(n) _____ solution.
hypertonic
You know that this cell is in a(n) _____ solution because it _____.
hypertonic solution ... lost water
You know that this cell is in a(n) _____ solution because the cell _____.
hypotonic ... swelled
Endocytosis moves materials _____ a cell via _____.
into ... membranous vesicles
Diffusion of ions across membranes through specific ion channels is driven by ________.
ion electrochemical gradients Submit
Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply.
lipids carbon dioxide oxygen
A human cell placed into a hypertonic solution is likely to
lose water by osmosis.
Which of the following organelles plays a primary role in the digestion of bacteria engulfed by white blood cells?
lysosomes
The voltage across a membrane is called the ________.
membrane potential
Which of the following membrane activities requires energy from ATP hydrolysis?
movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
Hydrophobic substances like salad oil are
nonpolar molecules that do not have an affinity for water molecules. Submit
In receptor-mediated endocytosis, membrane receptors bind to molecules outside of the cell. Immediately following endocytosis where will the membrane receptors be located?
on the inside surface of the vesicle
What name is given to the process by which water crosses a selectively permeable membrane?
osmosis
Facilitated diffusion is a type of _______.
passive transport
Which of the following cellular processes includes all of the others?
passive transport
Which of the following processes includes all the others?
passive transport
Which of the following types of molecules are most likely to be excluded from the hydrophobic portion of the phospholipid bilayer?
peripheral membrane proteins
A white blood cell engulfing a bacterium is an example of _____.
phagocytosis
Which of the following processes is used by white blood cells when engulfing bacteria?
phagocytosis
An organism with a cell wall would most likely be unable to take in materials through which of the following processes?
phagocytosis Submit
Identify Structure D.
phospholipid bilayer of membrane Submit
Which of the following statements best describes the difference between pinocytosis and receptor-mediated endocytosis?
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity Submit
When a person is dehydrated, his or her IV fluids
should be isotonic, because either a hypertonic or hypotonic IV would damage red blood cells.
Which of the following statements best describes the relationship between the solutions on both sides of the U-tube?
side A is isotonic to side B
Which of the following types of molecules will diffuse through a cell membrane most readily?
small hydrophobic molecules Submit
Which of the following types of molecules are least likely to diffuse through the phospholipid bilayer of a cell membrane?
small ions
What is the function of Structure E?
stabilization of the phospholipids
A human cell placed in a hypotonic environment would
take up water through osmosis. Submit
Many bacteria and fungi have a difficult time surviving on our food if the food is very salty. The best explanation for this is
that the salt in the food creates a hypertonic environment for the bacteria and fungi. Submit
You can recognize the process of pinocytosis when _____.
the cell is engulfing extracellular fluid
A new drug designed for the treatment of lung cancer must specifically enter the cytoplasm of lung cells while not entering the cells of other tissues. Which of the following characteristics would likely enhance the specificity of this drug?
the similarity of the drug molecule to other molecules normally transported lung cells
You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells.
the similarity of the drug molecule to other molecules that are transported into the target cells
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