Chapter 7 Mastering Bio
When the chamber containing the orange and purple dyes is at equilibrium, there are no concentration gradients between sides A and B. Which two of the following statements correctly describe the movement of dye molecules at equilibrium?
-For every orange dye molecule that moves from side A to side B, another orange dye molecule moves from side B to side A. -Each individual dye molecule moves in a random direction.
Vesicles are small membranous sacs found in the cytosol of all eukaryotic cells. Vesicles transport membrane components and other compounds between different parts of the endomembrane system, including the plasma membrane. Which of the following statements correctly describe the role of vesicles in exocytosis and endocytosis? Select the two that apply.
-Inward folding of the plasma membrane forms a vesicle that traps substances from outside the cell. -Fusion of a vesicle with the plasma membrane releases the contents of the vesicle outside the cell.
Because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). Together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. Consider the plasma membrane of an animal cell that contains a sodium-potassium pump as well as two non-gated (always open) ion channels: a Na+ channel and a K+ channel. The effect of the sodium-potassium pump on the concentrations of Na+ and K+ as well as the distribution of charge across the plasma membrane is indicated in the figure below. 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 diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. -The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. -The electrochemical gradient is larger for Na+ than for K+.
Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.
-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. -The diverse proteins found in and attached to membranes perform many important functions. -Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane.
Which of the following statements about the conditions shown in the U-shaped tube are true?
-Water is tightly clustered around the hydrophilic solute molecules on both sides of the membrane. -There is less free water in the right arm of the tube than in the left arm of the tube.
Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. 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 -water -oxygen -carbon dioxide
Under most conditions, cells have a negative membrane potential, meaning that the inside of the cell has more negative charge than the outside. This is equivalent to saying that the outside of the cell has more positive charge than the inside. Drag the phrases on the left to the appropriate blanks on the right to complete the sentences. Assume in all three cases that there is a concentration gradient for each solute to diffuse into the cell. 1. Negative membrane potential will _____ the diffusion of glucose into the cell 2. Negative membrane potential will _____ the diffusion of Cl ions into the cell 3. Negative membrane potential will _____ the diffusion of Mg ^2+ ions into the cell Decrease, Increase, Have no effect on
1. Negative membrane potential will have no effect the diffusion of glucose into the cell 2. Negative membrane potential will decrease the diffusion of Cl ions into the cell 3. Negative membrane potential will increase the diffusion of Mg ^2+ ions into the cell
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. 1. Orange dye moves independently of purple dye 2. Concentration gradients exist that drive diffusion of both dyes 3. There is a net movement of orange dye from side A to side B 4. Purple dye moves only from side B to side A 5. There is no net movement of purple dye Never, Always, Only before equilibrium is reached, Only at equilibrium
1. Orange dye moves independently of purple dye, Always 2. Concentration gradients exist that drive diffusion of both dyes, Only before equilibrium is reached 3. There is a net movement of orange dye from side A to side B, Only before the equilibrium is reached 4. Purple dye moves only from side B to side A, Never 5. There is no net movement of purple dye, Only at equilibrium
What are the characteristics of solutes that can pass through a lipid bilayer? Drag the phrases on the left to the appropriate blanks on the right to complete the sentences. 1. Solutes that can rapidly cross a lipid bilayer are typically _____. 2. Solutes that are _____ can cross a lipid bilayer, but not as quickly. 3. The lipid bilayer is essentially impermeable to solutes that are _____. Small and nonpolar, Small and polar, Charged
1. Solutes that can rapidly cross a lipid bilayer are typically small and nonpolar. 2. Solutes that are small and polar can cross a lipid bilayer, but not as quickly. 3. The lipid bilayer is essentially impermeable to solutes that are charged.
When comparing thermal motion and diffusion, it is important to distinguish between the movement of an individual molecule and the movement of a population of identical molecules. Drag the phrases on the left to the appropriate blanks on the right to complete the sentences. Not all phrases will be used. 1. The motion of _____is random whether or not a concentration gradient is present. 2. Diffusion is the net movement _____ when a concentration gradient is present. None of the dye molecules, An individual molecule, A population of dye molecules
1. The motion of an individual dye molecule is random whether or not a concentration gradient is present. 2. Diffusion is the net movement of a population of dye molecules when a concentration gradient is present.
Channels and carrier proteins are both involved in facilitated diffusion of certain solutes across the plasma membrane. Which of the following statements correctly describes the specificity of these transport proteins for the solutes they transport?
Channels typically transport water or inorganic ions, whereas carrier proteins typically transport small polar molecules such as sugars or amino acids.
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 _____ concentration and lower ____ concentration to the side with lower ____ concentration and higher ____ concentration.
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.
Na+ ions play an important role in most cotransport systems in animal cells. Recall that Na+ ions are pumped out of the cell by the action of the sodium-potassium pump. Which of the following statements correctly describes the movement of Na+ ions through cotransport proteins in animal cells?
Na+ ions move into the cell down their electrochemical gradient.
Which solutes are polar, nonpolar, and charged? -oxygen -Sucrose -ions -lipids -carbon dioxide -water -proteins
Polar: oxygen, carbon dioxide, lipids Nonpolar: sucrose, water, proteins Charged: ions
Consider three cells, each with a membrane potential of -100 mV. (There is excess negative charge inside the cell and excess positive charge outside.) Each scenario below represents the concentrations of a particular solute inside and outside the cell. Which scenario represents the largest electrochemical gradient for diffusion of the solute? Think about how the combined effects of the electrical gradient and the concentration gradient will affect the diffusion of each solute. Rank the three cells from smallest to largest electrochemical gradient. Keep in mind that each cell has the same membrane potential: -100 mV.
Smallest: [K+]= 1 mM [glucose]= 10 mM Largest: [Na+]= 10 mM
The sodium-potassium pump actively transports Na+ ions out of the cell and K+ ions into the cell. Which of the following statements correctly describes the effect the sodium-potassium pump has on the concentrations of Na+ and K+ across the plasma membrane?
The concentration of Na+ is greater outside the cell, and the concentration of K+ is greater inside the cell.
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.
The sodium-potassium pump actively transports three positively charged ions out of the cell and two positively charged ions into the cell. Which of the following statements correctly describes the effect the sodium-potassium pump has on the distribution of charge across the plasma membrane?
The outside of the cell is more positive than the inside because more positive ions are pumped out of the cell than are pumped in.
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
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
All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump. 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.
a. ^ 3 Na+ v 2 K+ b. Na+ high, K+ low c. excess + charge d. Na+ low, K+ high e. excess - charge
In many animal cells, the uptake of glucose into the cell occurs by a cotransport mechanism, in which glucose is cotransported with Na+ ions. 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.
a. glucose, low b. v glucose, v Na+ c. glucose high 1. Na + move down its electrochemical gradient. 2. Glucose moves against its concentration gradient.
Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both.
exocytosis: requires fusion of vesicles with the plasma membrane secretes large molecules out of the cell increases the surface area of the plasma membrane endocytosis: forms vesicles from inward folding of the plasma membrane decreases the surface area of the plasma membrane both: requires cellular energy transported substances never physically cross the plasma membrane
The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive movement of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. 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.
only channels: provide a continuous path across the membrane allow water molecules and small ions to flow quickly across the membrane only carriers: transport primarily small polar organic molecules undergo a change in shape to transport solutes across the membrane both: are integral membrane proteins provide a hydrophilic path across the membrane transport solutes down a concentration or electrochemical gradient
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