Mastering Biology Chapter 7

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

This figure reviews the structure of a phospholipid. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.

1. A phospholipid has a "head" made up of a glycerol molecule attached to a single phosphate group, which is attached to another small molecule.2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a choline group attached to phosphate.3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is hydrophilic, which means it has an affinity for water.4. A phospholipid also has two "tails" made up of two fatty acidmolecules, which consist of a carboxyl group with a long hydrocarbon chain attached.5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are hydrophobic, which means they are excluded from water.

1. Extracellular Fluid 2. Plasma Membrane 3. Cytoplasm

1. a. hydrophilice. hydrophilic c. hydrophilic2. f. hydrophobic 3. b. hydrophilic d. hydrophilic g. hydrophilic

A critical feature of the plasma membrane is that it is selectively permeable. This allows the plasma membrane to regulate transport across cellular boundaries--a function essential to any cell's existence. How does phospholipid structure prevent certain molecules from crossing the plasma membrane freely? Drag the labels to fill in the table.

1. a. hydrophobic b. crosses lipid bilayer easily c. no transport protein required 2. a. hydrophilic b. has difficulty crossing the lipid bilayer, the hydrophobic part c. transport protein required to cross efficiently 3. a. hydrophilic b. has difficulty crossing the lipid bilayer, the hydrophobic part c. transport protein required to cross efficiently

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. always2. only before equilibrium is reached 3. only before equilibrium is reached 4. never5. only at equilibrium

Which unknown solution contains the highest concentration of sucrose?

5

Which component in the figure above represents a protein fiber of the extracellular matrix?

A

Which of these can RAPIDLY pass directly through the phospholipids of the plasma membrane, without the help of a transport protein?

A only (lipid soluble molecule)

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.

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. Use targets of Group 1 to indicate the relative concentrations of Na+ and K+ inside and outside the cell. Use targets of Group 2 to indicate the relative charges inside and outside the cell. Use targets of Group 3 to indicate how many ions move through the pump and in which directions.

Active transport by the sodium-potassium pump follows this cycle.1. Three Na+ ions from the cytosol bind to the pump.2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP.3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell.4. 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.5. Release of the phosphate group causes another conformational change in the pump.6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature

Which of the following statements about osmosis is correct?

Aquaporins facilitate water movement across membranes and thus speed up the process of osmosis.

Which component in the accompanying figure plays a critical role in cell-cell recognition?

B

Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic to the solution in the beaker at 50 minutes?

B

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.

Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane.-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.

Which component in the figure above represents a microfilament of the cytoskeleton?

C

A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur.

Crenation ADE Hemolysis BC

Which component in the figure above represents cholesterol?

E

Which of the following statements correctly describes some aspect of exocytosis or endocytosis?

Exocytosis and endocytosis change the surface area of the plasma membrane.

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 molecules would likely diffuse through the lipid bilayer of a plasma membrane most rapidly?

O2

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) (Small nonpolar molecules such as oxygen can diffuse across cell membranes.)

A phospholipid bilayer with equal amounts of saturated and unsaturated fatty acids displays a specific permeability to glucose. What effect will increasing the proportion of unsaturated fatty acids in the bilayer have on the membrane's permeability to glucose?

Permeability to glucose will increase.

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 (The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.)

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.

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.

Which statement is correct?

The contents of a red blood cell are hyperosmotic to distilled water.

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 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+.-The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane.

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.

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.

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.

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 factors would tend to increase membrane fluidity

a greater proportion of unsaturated phospholipids

Which of the following factors would tend to increase membrane fluidity?

a greater proportion of unsaturated phospholipids

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 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. Use targets of Group 1 to indicate the relative concentration of glucose inside and outside the cell. Use targets of Group 2 to indicate the direction that Na+ ions and glucose move through the cotransporter. Use targets of Group 3 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. decrease in glucose and Na+-Na+ moves down its electrochemical gradient -Glucose moves against its concentration gradient c. glucose high

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

Which of the following types of molecules are most likely to lack hydrophilic domains?

cholesterol

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 pH

Which of the following factors is a primary contributor underlying cause of familial hypercholesterolemia?

defective LDL receptors on the cell membranes

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

Sort the phrases into the appropriate bins depending on whether they describe exocytosis, endocytosis, or both.

exocytosis: -increases the surface area of the plasma membrane-requires fusion of vesicles with the plasma membrane-secretes large molecules out of the cellendocytosis: -decreases the surface area of the plasma membrane-forms vesicles from inward folding of the plasma membraneboth: -requires cellular energy-transported substances never physically cross the plasma membrane

Identify Structure A.

glycoprotein

This cell is in a(n) _____ solution.

hypertonic

Endocytosis moves materials _____ a cell via _____.

into ... membranous vesicles

The voltage across a membrane is called the ________.

membrane potential

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

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 membraneonly carriers: -undergo a change in shape to transport solutes across the membrane-transport primarily small polar organic moleculesboth:-transport solutes down a concentration or electrochemical gradient -are integral membrane proteins -provide a hydrophilic path across the membrane

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.

oxygen lipids water carbon dioxide

Facilitated diffusion is a type of _______.

passive transport

which process contains all 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

Identify Structure D.

phospholipid bilayer of membrane

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

In what way do the membranes of a eukaryotic cell vary?

proteins contained

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 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

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

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

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

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

Structure A in the figure is a(n) _____.

transport protein

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