In what way do the membranes of a eukaryotic cell vary?
Certain proteins are unique to each membrane.
According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly
embedded in a lipid bilayer.
Which of the following factors would tend to increase membrane fluidity?
a greater proportion of unsaturated phospholipids
Which of the following processes includes all others?
Which statement is correct?
The contents of a red blood cell are hypertonic to distilled water.
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.
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.
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.
Select the correct statement about osmosis.
Osmosis is the diffusion of water molecules across a selectively permeable membrane.
Based on Figure 7.18 in your textbook, which of these experimental treatments would increase the rate of sucrose transport into the cell?
decreasing extracellular pH
What is the function of Structure E?
stabilization of the phospholipids
Identify Structure D.
phospholipid bilayer of membrane
Identify Structure A.
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 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
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 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
For a protein to be an integral membrane protein, it would have to be _____.
amphipathic, with at least one hydrophobic region
You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane’s permeability to glucose?
Permeability to glucose will increase.
According to the fluid mosaic model of cell membranes, phospholipids _____.
can move laterally along the plane of the membrane
The membranes of winter wheat are able to remain fluid when it is extremely cold by _____.
increasing the percentage of unsaturated phospholipids in the membrane
Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions _____.
are less fluid than the surrounding membrane
Singer and Nicolson’s fluid mosaic model of the membrane proposed that membranes_____.
consist of protein molecules embedded in a fluid bilayer of phospholipids
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function?
Which of these are NOT embedded in the hydrophobic portion of the lipid bilayer at all?
Why are lipids and proteins free to move laterally in membranes?
There are only weak hydrophobic interactions in the interior of the membrane.
Which component is a peripheral protein?
Which component is cholesterol?
Which component is a protein fiber of the extracellular matrix?
Which component is a microfilament (actin filament) of the cytoskeleton?
Which component is a glycolipid?
Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane’s asymmetrical nature?
The two sides of a cell membrane face different environments and carry out different functions.
Which of the following is a reasonable explanation for why unsaturated fatty acids help keep a membrane more fluid at lower temperatures?
The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.
*Membranes consist of diverse proteins suspended in and attached to a phospholipid bilayer. Kinks in the unsaturated fatty acid tails of some phospholipids keep the membrane fluid, and a mosaic of proteins perform a variety of functions.
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
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.
Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
the similarity of the drug molecule to other molecules that are transported into the target cells
Structure A in this animation is a(n) _____.
Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?
B, C, and D
Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
Drag the labels to their appropriate locations in the figure.
First, drag labels to targets (a) and (b) to indicate whether these environments are hydrophilic or hydrophobic.
Next, drag the phospholipid layers to targets (c) and (d) to indicate how they are oriented in the plasma membrane.
Finally, drag labels to targets (e), (f), and (g) to indicate which portions of the membrane protein are hydrophilic and which are hydrophobic.
c. tail face down
d. tail face up
Drag the labels to fill in the table. Use only white labels for white targets, pink labels for pink targets, and blue labels for blue targets.
b. can cross easily
c. no transport protein required
e. have difficulty crossing the hydrophobic part
f. transport protein required to cross efficiently
h. have difficulty crossing the hydrophobic part
i. transport protein required to cross efficiently
What kinds of molecules pass through a cell membrane most easily?
small and hydrophobic
Which of the following most accurately describes selective permeability?
Only certain molecules can cross a cell membrane.
Which of the following is a characteristic feature of a carrier protein in a plasma membrane?
It exhibits a specificity for a particular type of molecule.
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly?
Which of the following allows water to move much faster across cell membranes?
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. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
similarity of the drug molecule to other molecules transported by the target cells
A semipermeable membrane is placed between the following solutions.
Which solution will decrease in volume?
Solution A: 1.4% (m/v) starch
Which solution will increase in volume?
Solution D: 12.4% (m/v) NaCl
A red blood cell has been placed into three different solutions. One solution is isotonic to the cell, one solution is hypotonic to the cell, and one solution is hypertonic to the cell. Determine which type of solution is in each beaker based on the cell’s reaction.
Drag each item to the appropriate bin.
*For a cell in an isotonic solution, water flows into the cell to the same extent that it flows out of the cell. If a cell is in a hypotonic solution, water flows into the cell, which causes it to swell and potentially burst. For a cell in a hypertonic solution, water flows out of the cell, which causes it to shrink.
A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur.
Solution A: 3.21% (m/v) NaCl
Solution B: 1.65% (m/v) glucose
Solution C: distilled H2O
Solution D: 6.97% (m/v) glucose
Solution E: 5.0% (m/v) glucose and 0.9%(m/v) NaCl
Drag each solution to the appropriate bin.
crenation: a d e
hemolysis: b c
What name is given to the process shown in this animation?
What name is given to the process by which water crosses a selectively permeable membrane?
This cell is in a(n) _____ solution.
You know that this cell is in a(n) _____ solution because the cell _____.
hypotonic … swelled
Click on the cell to start the animation. This plant cell is _____.
in a hypotonic solution
You know that this cell is in a(n) _____ solution because it _____.
hypertonic solution … lost water
The process shown in this animation is referred to as _____.
Structure A is a _____.
Structure B is a _____.
All molecules have energy that causes thermal motion. One result of thermal motion is diffusion: the tendency of substances to spread out evenly in the available space. Although the motion of each individual molecule is random, there can be directional motion of an entire population of 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. Initially (left image), the concentration of the orange dye is greater on side A, and the concentration of the purple dye is greater on side B. With time, the dye molecules diffuse to a final, equilibrium state (right image) where they are evenly distributed throughout the chamber.
Two diagrams showing a chamber containing purple and orange balls–one before diffusion and one after diffusion. The chamber is divided into two compartments by a membrane that is permeable to both purple and orange balls. The diagram on the left shows the initial condition, with 9 orange balls on the left side of the membrane and 3 orange balls on the right. There are 2 purple balls on the left and 6 purple balls on the right. The diagram on the right shows the equilibrium state after diffusion has occurred. There are 6 orange balls on the left and 6 orange balls on the right. There are 4 purple balls on the left and 4 purple balls on the right.
Drag the labels onto the table to indicate when each statement is true. Labels can be used once, more than once, or not at all.
only before equilibrium is reached
only before equilibrium is reached
only at equilibrium
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.
*Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all.
Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer.
Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer.
Polar molecules such as glucose and sucrose have very limited permeability.
Large molecules such as proteins cannot pass through the lipid bilayer.
Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.
Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers.
*Carrier proteins and channels are both transport proteins involved in facilitated diffusion, the passive transport of solutes across a membrane down their concentration or electrochemical gradient. As integral membrane proteins, both carriers and channels protect polar or charged solutes from coming into contact with the hydrophobic interior of the lipid bilayer. Furthermore, all transport proteins are specific for the solutes they transport, owing to the specificity of the interactions between the solute and the transport protein.
Which of the following factors does not affect membrane permeability?
The polarity of membrane phospholipids
How can a lipid be distinguished from a sugar?
Lipids are mostly nonpolar.
True or false? Osmosis is a type of diffusion.
What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
Which of the following particles could diffuse easily through a cell membrane?
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.
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?
Which of the following statements about osmosis is correct?
The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis.
In facilitated diffusion, what is the role of the transport protein?
Transport proteins provide a hydrophilic route for the solute to cross the membrane.
Which variable is the independent variable–the variable that was controlled by the researchers? Is the independent variable on the x-axis or the y-axis?
incubation time; on the x-axis
Which variable is the dependent variable–the variable that depended on the treatment and was measured by the researchers? Is the dependent variable on the x-axis or the y-axis?
concentration of radioactive glucose; on the y-axis
What do the red dots represent?
the concentration of radioactive glucose found in a 15-day-old guinea pig’s red blood cells after different incubation times
What do the blue dots represent?
the concentration of radioactive glucose found in a 1-month-old guinea pig’s red blood cells after different incubation times
What concentration of radioactive glucose did the researchers find in the red blood cells of a 15-day-old guinea pig after an incubation time of 30 minutes?
Identify the trend common to both the 15-day-old and 1-month-old guinea pigs’ red blood cells.
Both experienced the most rapid uptake of glucose at the beginning of the experiment.
What is the main difference between the trends for the 15-day-old and 1-month-old guinea pigs’ red blood cells?
The younger guinea pig’s cells took up more glucose than the older guinea pig’s cells at all incubation times.
Which of the following hypotheses is a reasonable explanation for the data represented in the graph?
The red blood cells of older guinea pigs have fewer glucose transporter proteins than the red blood cells of younger guinea pigs.
is a passive process in which molecules move from a region of higher concentration to a region of lower concentration
When a cell is in equilibrium with its environment, which of the following occurs for substances that can diffuse through the cell?
There is random movement of substances into and out of the cell.
Which of the following is true of osmosis?
In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
Refer t o the figure. Initially, in terms of tonicity, the solution in side A with respect to the solution in side B is _____.
Refer to the figure. After the system reaches equilibrium, what changes are observed?
The water level is higher in side A than in side B.
A patient was involved a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled waterequal to the volume of blood lostis added to the blood directly via one of his veins. What will be the most probable result of this transfusion?
The patient’s red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.
Refer to the figure. At the beginning of the experiment,
side A is hypotonic to side B.
Refer to the figure. If you examine side A after three days, you should find _____.
a decrease in the concentration of NaCl and a decrease in the water level
Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?
Which line in the graph represents the bag with the highest initial concentration of sucrose?
Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes?
Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.
is hypotonic and the salt solution is hypertonic to the cells of the celery stalks
What will happen to a red blood cell (RBC), which has an internal ion concentration of about 0.9 percent, if it is placed into a beaker of pure water?
The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.
Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in _____.
an isotonic solution, and the plant cell is in a hypotonic solution
In which of the following would there be the greatest need for osmoregulation?
a salmon moving from a river into an ocean
When a plant cell, such as one from a rose stem, is submerged in a very hypotonic solution, what is likely to occur?
The cell will become turgid.
Three lab groups carried out an experiment to identify the correct molarities for five solutions. Each unknown 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. Each data entry represents the average of 3 sample replications of 1 cm3 sweet potato cubes expressed as percent change in mass after an overnight (24 hr) soak in the unknown solutions. From the data given, which statement most accurately describes what is occurring in response to a particular unknown solution.
Osmosis of water molecules from unknown solution A likely caused the increase in mass observed.
Which of the following statements is TRUE with regard to this animation?
Both sodium and potassium ions are transported against their concentration gradients.
Complete the diagram below using the following steps.
Drag the correct white label to the white target, indicating how many ions move through the pump and in which directions.
Drag the pink labels to the pink targets, indicating the relative concentrations of Na+ and K+ inside and outside the cell.
Drag the blue labels to the blue targets, indicating the relative charges inside and outside the cell.
**Active transport by the sodium-potassium pump follows this cycle.
The number one, corresponding to step one in a diagram below the text. Three Na+ ions from the cytosol bind to the pump.
The number two, corresponding to step two in the diagram below the text. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP.
The number three, corresponding to step three in the diagram below the text. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell.
The number four, corresponding to step four in the diagram below the text. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released.
The number five, corresponding to step five in the diagram below the text. Release of the phosphate group causes another conformational change in the pump.
The number six, corresponding to step six in the diagram below the text. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.
A diagram showing six steps of active transport in the sodium-potassium pump. Each numbered step corresponds to the text above.
The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane.
The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane.
Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.
*The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell.
The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell.
The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.
Complete the diagram below using the following steps.
Drag the pink labels to the pink targets, indicating the relative concentration of glucose inside and outside the cell.
Drag the correct white label to the white target, indicating the direction that Na+ ions and glucose move through the cotransporter.
Drag the blue labels to complete the sentences on the right, indicating how Na+ ions and glucose move through the cotransporter relative to their electrochemical and concentration gradients.
In cotransport, the energy required to move one solute against its concentration or electrochemical gradient is provided by an ion moving into the cell down its electrochemical gradient. The ion that moves into the cell down its gradient is usually the same ion that is pumped out of the cell by an active transport pump: for example, Na+ in animal cells using the sodium-potassium pump, or H+ in plants and prokaryotes using the proton pump.
In the case of the glucose-sodium cotransporter in animals, Na+ moves back into the cell down its electrochemical gradient, providing the energy for glucose to move into the cell against its concentration gradient. The energy for glucose transport into the cell is supplied indirectly by the sodium-potassium pump’s hydrolysis of ATP, and directly by the Na+ electrochemical gradient created by the pump.
What distinguishes facilitated diffusion from simple diffusion?
Membrane proteins help move molecules across the membrane.
Which of the following transporters does not use passive transport to move molecules across a membrane?
True or false? Active transport differs from passive transport in that active transport does not require an input of energy.
Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration?
Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?
The charge on the other side of the membrane is generally the opposite of the ion’s charge.
True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell for every two potassium ions pumped out of the cell.
Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration outside the cell. What type of transport is used to move lactose into 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?
The movement of glucose into a cell against a 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
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 sodium-potassium pump _____.
move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle
Which of the following membrane activities requires energy from ATP?
movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
The voltage across a membrane is called the _____.
Ions diffuse across membranes through specific ion channels down _____.
their electrochemical gradients
Which of the following would increase the electrochemical gradient across a membrane?
a proton pump
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. Phosphate import depends on a pH gradient across the membrane (more acidic outside the cell than inside the cell). Phosphate transport is an example of _____.
In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by _____.
Which of the following is most likely true 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.
Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?
Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
Several epidemic microbial diseases of earlier centuries incurred high death rates because they resulted in severe dehydration due to vomiting and diarrhea. Today they are usually not fatal because we have developed which of the following?
hydrating drinks with high concentrations of salts and glucose
The force driving simple diffusion is _____, while the energy source for active transport is _____.
the concentration gradient; ATP
Endocytosis moves materials _____ a cell via _____.
into … membranous vesicles
Click on the vesicle to start the animation. This is an animation of _____.
Click on the brown debris to start the animation. This is an animation of _____.
Click on the extracellular fluid to start the animation. You know that this process is _____ because _____.
pinocytosis … the cell is engulfing extracellular fluid
Click on the receptor protein to start the animation. This is an animation of _____.
A white blood cell engulfing a bacterium is an example of _____.
Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both.
*In exocytosis, substances are transported to the plasma membrane in vesicles derived from the endomembrane system. These vesicles fuse with the plasma membrane, releasing the enclosed substances outside the cell.
In endocytosis, substances are taken into the cell by folding in of the plasma membrane and pinching off of the membrane to form a vesicle. Notice that in both exocytosis and endocytosis, the transported substances never actually cross the plasma membrane as they leave or enter the cell.
Which of the following correctly describes some aspect of exocytosis or endocytosis?
Exocytosis and endocytosis change the surface area of the plasma membrane.
An organism with a cell wall would most likely be unable to take in materials through _____.
White blood cells engulf bacteria using _____.
Familial hypercholesterolemia is characterized by _____.
defective LDL receptors on the cell membranes
The difference between pinocytosis and receptor-mediated endocytosis is that _____.
pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis?
on the inside surface of the vesicle
A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in _____.
In an HIV-infected cell producing HIV virus particles, the viral glycoprotein is expressed on the plasma membrane. How do the viral glycoproteins get to the plasma membrane? They are synthesized _____.
by ribosomes in the rough ER and arrive at the plasma membrane in the membrane of secretory vesicles
What would be observed by live-cell fluorescence microscopy immediately after HIV entry if HIV is endocytosed first, and then later fuses with the endocytotic vesicle membrane?
The red fluorescent dye-labeled lipids will appear in the infected cell’s interior.
Which of the following is NOT a function of membrane proteins?
energy, carbon, and nitrogen storage
Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals?
Membrane proteins with short sugar chains form identification tags that are recognized by other cells.
Which of the following statements concerning carbohydrates associated with the plasma membrane is correct?
Membrane carbohydrates function primarily in cell-cell recognition.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found?
on the outside (external) surface of the membrane
Can you label some components associated with the plasma membrane and identify the functions of membrane proteins?
a. phospholipid bilayer
b. fibers of extracellular matrix (ECM)
c. enzymatic activity
d. microfilaments of cytoskeleton
e. attachment to ECM and cytoskeleton
f. signal transduction
h. intercellular junctions
i. cell-cell recognition
Can you match the processes involved in membrane transport to their descriptions?
Which of the following processes and organelles account for the replacement of lipids and proteins lost from the plasma membrane?
exocytosis and smooth ER and rough ER
Which of the following statements about cotransport of solutes across a membrane is correct?
Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.
The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution?
Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside of the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. Which of the following statements about this mechanism is accurate?
To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.
A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition?
Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease.
Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein?
The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time.
Which of the following statements about passive transport is correct?
Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule.
In active transport,
molecules move across the plasma membrane against their concentration gradient.
A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of
Water crosses the plasma membrane
through facilitated diffusion or diffusion.
The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of
The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of
Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells?
Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall.
Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B. and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.
B … the diffusion gradient in cell B is steeper
Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true?
The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane.
The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
a hypertonic sucrose solution
Which of the following cell structures exhibits selective permeability between a cell and its external environment?
the plasma membrane
Some large molecules move into or out of cells by exocytosis or endocytosis.
Which of the following statements about diffusion is true?
It is a passive process.
Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives?
A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis.
Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct?
Phospholipids form a selectively permeable structure.
Which of the following is a correct difference between active transport and facilitated diffusion?
Active transport requires energy from ATP, and facilitated diffusion does not.
Which of the following statements about the sodium-potassium pump is correct?
The sodium-potassium pump moves Na+ and K+ in opposite directions, resulting in a net negative charge inside the cell.
Certain molecules use diffusion to cross the plasma membrane.
a. side with higher concentration of molecules
b. plasma membrane
c. side with lower concentration of molecules
d. diffusion causes a net movement of molecules down their concentration gradient
Which of the following would be LEAST likely to diffuse through a plasma membrane without the help of a transport protein?
a large, polar molecule
Can you match these three tonicity terms with their descriptions?
Which of the following enables a cell to pick up and concentrate a specific kind of molecule?
A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change?
Nothing will happen, because the two solutions are isotonic to one another.