Chapter 5: Membranes
What component of plant cells prevents changes in cell volume that result in osmotic lysis?
cell wall
Eukaryotic cells can transport large molecules such as proteins and polysaccharides via __________ and ____________. Both of these mechanisms involve membrane vesicles or vacuoles.
endocytosis, exocytosis
Plasmolysis occurs when water
exits a plant cell and the cell membrane pulls away from the cell wall.
What processes are used by eukaryotic cells to transport large molecules such as proteins and polysaccharides?
endocytosis and exocytosis
When the solute concentration is higher inside the cell relative to outside the cell, the outside solution is said to be
hypotonic
When the solute concentration is higher inside the cell relative to outside the cell, the outside solution is said to be:
hypotonic
If the medium surrounding a plant cell is hypertonic, water exits the cell and the cell membrane pulls away from the cell wall in a process known as
plasmolysis
What is the result of placing a plant cell into a hypertonic solution?
plasmolysis
The presence of a double bond in a phospholipid tail makes the membrane more fluid because
it prevents phospholipids from packing tightly.
What characteristics would a solute with very low membrane permeability have?
large and charged
Because transmembrane proteins are much ___________ than lipids, they diffuse within the membrane at a ____________ rate.
larger, slower
Gated channels can be opened or closed by the binding of small molecules called
ligands
A term that describes a situation in which the concentration of a solute is higher on one side of a membrane than the other is
transmembrane gradient
Membrane proteins that span both leaflets of the lipid bilayer are called
transmembrane protein
Endocytosis and exocytosis involve packaging substances into a membrane-enclosed
vacuole or vesicle
The major finding of the experiment by the 1980s researchers led by Agre is the existence of a protein for the facilitated diffusion of
water
Which of the following can readily diffuse across the cell membrane?
Small, uncharged molecules Gases
In animals, anchoring junctions attach adjacent cells to each other and to the ____________ matrix.
extracellular
Protein channels that open and close in response to the binding of a ligand are called
gated ligands
Gap junctions in vertebrates are composed of
connexin
Membrane fluidity is increased when membrane lipids
have shorter nonpolar tails
The Na+/K+ -ATPase produces an electrical gradient across the membrane because one cycle of pumping results in the NET
export of one positive charge
Movements that keep the phospholipid nonpolar tail within the _____________ region of the bilayer are energetically favorable.
hydrophobic
When a double bond is present in the nonpolar tail of a phospholipid, the lipid is said to be
unsaturated
Osmosis is the flow of ___________ across a membrane.
water
While individual cells have many types of transport proteins in their membranes, the cells of multicellular organisms also may have ______ that allow the movement of substances between adjacent cells.
intercellular channels
The structure of a tight junction is best described as
interlaced strands of protein.
Arrange the following solutes based on their membrane permeability. Start at the top with the solute that has the highest membrane permeability.
oxygen gas, water, glucose, potassium ions
Small, uncharged molecules pass through the membrane via
passive diffusion
Proteins that associate with the plasma membrane through non-covalent interactions with phospholipids or transmembrane proteins are called __________ membrane proteins.
peripheral
Certain kinds of cells can engulf large particles, such as bacteria, through a type of endocytosis called
phagocytosis
The plasma membrane consists of a(n) ____________ bilayer.
phospholipid
What is the basic structure of the plasma membrane
phospholipid bilayer
During a type of endocytosis called _____________, vesicles from the plasma membrane form and allow cells to internalize the extracellular fluid.
pinocytosis
During a type of endocytosis called ______________ , vesicles from the plasma membrane form and allow cells to internalize the extracellular fluid.
pinocytosis
The formation of vesicles from the plasma membrane allows cells to internalize the extracellular solutes during:
pinocytosis
The cytosolic leaflet of the plasma membrane faces:
the inside of the cell
Transporter proteins are classified by which of the following?
the number of solutes they bind the direction of transport
The two leaflets of a lipid bilayer are formed because
the polar head groups of phospholipids can interact with the polar interior and exterior of the cell.
What is one way that solutes that cannot diffuse across the membrane can still gain access to the interior of the cell?
transportation proteins
Which type of protein is the principal pathway for the uptake of sugars, amino acids, and nucleotides?
transporter proteins
Transmembrane protein flip-flop does not occur spontaneously because it would be energetically
unfavorable
Transporters that bind a single ion or molecule and move it across the membrane are called .
uniporters
In both endocytosis and exocytosis, the transported substance is packaged into a(n):
vesicle
Unlike transporters, __________ proteins provide an open passageway all the way across the plasma membrane.
channel
Proteins that assist in the movement of substances across membranes can be classified into two types based on how they move solutes across a membrane:
channels, transporters
What categories of proteins assist in the movement of molecules and ions across
channels, transporters
When plasmodesmata are dilated, they allow the passage of
macromolecules and viruses
Within the plasma membrane, where are glycolipids normally found?
extracellular leaflet
Cholesterol in a membrane has which of the following effects?
At a high temperature, it makes the membrane less fluid; at a low temperature, it makes the membrane more fluid.
Why is the Na+/K+-ATPase pump considered an antiporter?
Because it moves two substances in opposite directions.
A(n) ______ is a special channel protein that allows the facilitated diffusion of water.
aquaporin
Some transmembrane proteins are restricted in their movement because they contain regions that project into the cytosol and are anchored to components of the
cytoskeleton
Tight junctions are mechanically weaker than anchoring junctions because they do not have strong connections with the ______________ of the cell.
cytoskeleton
Which type of anchoring junction contains cadherins that connect cells to each other and to intermediate filaments in the cytosol?
desmosome
In a desmosome, proteins called _______________ connect cells to each other. In the cytosol, desmosomes are connected to _______________ filaments.
cadherins, intermediate
An unsaturated lipid contains
double bonds
One layer, or half of a phospholipid bilayer, is termed a(n)
leaflet
Phospholipid bilayers are an effective barrier to many charged or polar solutes because of their ____________ interior region.
hydrophobic
When the concentration of solutes outside the cell is higher than that intra-cellularly, the solution is said to be __________ relative to the inside of the cell.
hypertonic
A contractile vacuole is an important feature of microorganisms living in a(n)
hypotonic
What do gap junctions do in animals?
Provide passageways for intercellular transport
group of lipids that float together as a unit within the plasma membrane is called a(n)
lipid raft
A membrane protein with a lipid covalently bound to an amino acid side chain within the protein is known as a(n)
lipid-anchored protein
Which of the following can be found in lipid rafts?
lipid-anchored proteins high amount of cholesterol transmembrane proteins
What processes are coupled across cell membranes
The import of K+ ions The export of Na+ ions
When mouse and human cells are combined, their membrane proteins
mix at incubation temperatures typical of mammals.
Shorter nonpolar tails make the membrane ______ fluid.
more
Because the plasma membrane contains lipids, proteins, and carbohydrates, it is often described as a(n)
mosaic
A lipid bilayer is composed of ______ leaflet(s).
2
How many conformational states does the Na+/K+ -ATPase pump have?
2
Which of the following statements is correct about a biological membrane that is fluid?
Individual molecules can move within the membrane.
Diffusion
Movement of a substance from a region where its concentration is high to a region where its concentration is low
fascilitated diffusion
Movement of a substance from a region where its concentration is high to a region where its concentration is low through a passageway provided by a transport protein
Which of the following statements explain why the phospholipid bilayer is composed of two leaflets?
Phospholipids are amphipathic and must interact with polar and nonpolar environments. Hydrophobic nonpolar tails can be isolated into a hydrophobic environment between the two leaflets. Membranes must interact with two polar environments, a hydrophilic cytoplasm and a hydrophilic extracellular environment.
Which of the following properties are shared by phospholipids and transmembrane proteins?
They both move laterally in the plane of the membrane. They are both composed of polar and non-polar regions.
How do transporters differ from channel proteins?
Transporters must change conformation to allow solutes to cross the membrane.
Transporter proteins transport solutes across the membrane via:
a conformational change triggered by solute binding
Lipid-anchored proteins typically associate with
a membrane
Why can nitrogen gas diffuse through the lipid bilayer but a nitrogen ion cannot?
a nitrogen ion carries a charge
A phospholipid molecule consists of
a polar head and two nonpolar tails
An electrochemical gradient occurs in solutions that have
a positive or negative charge
To move a substance through a membrane against a concentration gradient, which of the following are necessary?
a transport protein and a source of energy
Select the two types of cell adhesion molecules (CAMs).
cadherins and integrins
Transporter proteins bind their solutes in a hydrophilic pocket and then undergo a(n) ____________ change that switches the exposure of the pocket from one side of the membrane to the other.
conformational
In a gap junction, an intercellular channel is formed by the alignment of channels called ______ in adjacent cells.
connexons
Which of the following statements regarding adherens junctions are true?
contain cadherins bind to actin filaments in the cytosol
A gradient that includes both electrical and chemical components is called a(n)
electrochemical
__________ gradients are used for many different functions, including bacterial swimming, nerve signaling, and osmotic regulation.
electrochemical
A pump that creates an electrical gradient is called a(n):
electrogenic pump
The transportation of a solute against its chemical or electrochemical gradient requires a source of
energy
Abnormalities in cadherins and integrins can affect the
intracellular signal transduction pathways.
The first step in ____________ -mediated endocytosis is the binding of a cargo molecule to a membrane protein. Listen to the complete question
receptor
The type of endocytosis in which cell surface receptors ensure specificity of transport is called ______________ - ___________ endocytosis.
receptor-mediated
A solution in which the solute concentration on both sides of the membrane is equal is classified as
isotonic
When the concentrations of dissolved particles (solutes) on both sides of the plasma membrane are equal, the two solutions are said to be
isotonic
In Peter Agre's experiment, what was the experimental (1) and control (2) treatment of oocyctes?
(1) Injected with CHIP28 mRNA, (2) not injected with CHIP28 mRNA; both in hypotonic medium
The Na+/K+ -ATPase pumps ______ Na+ ions out of the cell and ______ K+ ions into the cell.
3, 2
How many connexin proteins in total are needed to create a connexon in one vertebrate cell?
6
What is a lipid raft?
A group of lipids that associate as a unit within a membrane
Lipid-anchored protein
A lipid molecule is covalently attached to an amino acid side chain of the membrane protein.
Transmembrane protein
A segment of amino acids is inserted into the phospholipid bilayer.
Uniporter
A single solute moves in one direction. matches
The sodium/potassium -ATPase transports Na+ and K+ ions against their gradients using the energy from _____________ hydrolysis
ATP
The transfer of phospholipids between leaflets requires the input of
ATP
Which of the following could provide energy to fuel active transport?
ATP
Which of the following molecules can pass through plasmodesmata?
ATP sugars ions
What types of transport require a transport protein?
Active transport Facilitated diffusion
Which of the following anchoring junctions bind to actin filaments in the cytoskeleton?
Adherens junctions Focal adhesions
Select all the functions of anchoring junctions.
Attach cells to each other Bond cells to the extracellular matrix
Which of the following can restrict the movement of transmembrane proteins?
Attachment to cytoskeletal filaments Attachment to the extracellular matrix
Why is the phospholipid bilayer an effective barrier to hydrophilic or polar molecules?
Because of the hydrophobic interior of the bilayer
Select the true statements comparing simple and facilitated diffusion.
Both simple and facilitated diffusion require concentration gradients. Facilitated diffusion, but not simple diffusion, requires a transport protein.
An experiment by Agre and colleagues showed that frog oocytes that expressed CHIP28 took on water in a hypotonic medium, while those that did not express it did not. These results support the hypothesis that
CHIP28 functions as a transport protein that allows the facilitated diffusion of water across the membrane.
How do conformational changes of the Na+/K+-ATPase pump relate to its function?
Conformational changes allow the pump to access either the cytosol or the outside of the cell. Conformational changes allow solutes bound on one side of the membrane to be moved to the other side. Conformational changes expose binding surfaces for both Na+ and K+.
How is a lipid-anchored protein attached to the membrane?
Covalently bound to an amino acid side chain within the protein
What is osmosis?
Diffusion of water from an area of low solute concentration to an area of high solute concentration
Which of the following are conformational states of the Na+/K+-ATPase pump?
E2 E1
The vesicles involved in exocytosis are usually derived from the
Golgi apparatus
What is the significance of being able to gate a channel protein?
Gating a channel protein allows the cell to regulate the movement of solutes.
What organelle is the origin of the vesicles used in exocytosis?
Golgi apparatus
The symporters of bacteria, fungi, algae, and plant cells usually rely on a(n) ______ gradient across their plasma membranes, while the symporters of animal cells typically use a(n) ______ gradient.
H+ ; Na+
The H+/sucrose symporter is used to bring both H+ and sucrose into the cell. How are each of the two solutes transported into the cell?
H+ moves down its electrochemical gradient, while sucrose is actively transported.
What changes might occur in the membranes of a polar bear's cells when hibernating over the winter?
It might incorporate more cholesterol into its membrane to make it more fluid.
What are likely binding sites for peripheral membrane proteins?
Hydrophilic regions of integral membrane proteins Polar head groups of phospholipids
Which of the following changes in lipid composition would be expected to increase the fluidity of a phospholipid bilayer?
Incorporating more cholesterol at low temperatures Incorporating more unsaturated fatty acids
A plant responding to a change in temperature alters its lipid composition to have longer fatty acid tails and fewer double bonds. What effect on the membrane will this have?
It becomes less fluid in response to high temperatures.
How does cholesterol affect the plasma membrane at low temperatures?
It makes the membrane more fluid and prevents freezing.
In the 1940s, studies of animal cells suggested that the import of ______ is coupled to the export of ______.
K+, Na+
In the Frye and Edidin experiment, how did temperature affect lateral protein movement?
Lateral protein movement was inhibited at low temperatures.
active transport
Movement of a substance from a region where its concentration is low to a region where its concentration is high with the aid of a transport protein and a source of energy
The structure of the Na+/K+-ATPase pump allows the binding of which of the following?
Na+ K+
The Na+/K+-ATPase pump establishes and maintains a gradient such that:
Na+ is higher outside the cell than inside, and K+ is higher inside the cell than outside
In bacteria, fungi, algae, and plant cells, symporters usually rely on a proton gradient across the plasma membrane. In animal cells, however, most symporters rely on a(n)
Na+ sodium gradient
Which of the following are membrane proteins found in tight junctions?
Occludin Claudin
Peripheral membrane protein
Noncovalent associations form with phospholipids or other membrane proteins
Which of the following best describes the process of active transport?
Particles moving across a membrane against a concentration gradient.
Which of the following statements are consistent with the fluid-mosaic model
Phospholipids can move within the plane of the membrane. Many membrane proteins move within the plane of the membrane. Membranes are mainly composed of proteins and phospholipids.
Why is it more appropriate to describe membranes as semifluid
Phospholipids usually move in two dimensions. Molecules move laterally within the membrane leaflet.
Which of the following move solutes in only one direction?
Symporters Uniporters
Symporter
Two solutes move in one direction. matches
Antiporter
Two solutes move in opposite directions. matches
An animal cell is placed in a hypertonic medium. Predict which way water will move
Water will move from the inside of the cell to the outside.
An animal cell is placed in pure water (which contains no solutes). In what direction will water move?
Water will move into the cell from the outside.
What is an aquaporin?
a channel protein for water
A cell contains a higher concentration of glucose than the surrounding environment. What type of transport is required to import glucose into the cell?
active transport
ATP can be used to power which of the following processes?
active transport
The transport of a substance that requires an input of energy is called
active transport
Active transport is the movement of a solute across the membrane ____________ its concentration gradient.
against
The Na+/K+ -ATPase actively transports Na+ and K+ ions ___________ their gradients by using the energy from ATP hydrolysis.
against
In multicellular organisms, intercellular channels such as gap junctions in animals and plasmodesmata in plants
allow the movement of substances between adjacent cells.
Most transmembrane segments of integral membrane proteins are folded into what type of secondary structure?
alpha helix
Which of the following can pass through gap junctions?
amino acids cAMP calcium ions (they are too small for RNA and proteins)
Arrange the solutes that are listed according to a phospholipid bilayer's permeability to them. Place the substance with the lowest permeability at the top, and that with the highest permeability at the bottom.
amino acids, sugar, urea, carbon dioxide
Phospholipids have both hydrophobic and hydrophilic components. As such, they are said to be
amphipathic
Moving a solute from areas of low concentration to high concentration requires:
an input of energy
The difference between passive transport and active transport is that active transport requires
an input of energy
Cellular membranes play a role in which of the following cell functions?
anchoring the cytoskeleton cell and nuclear division cell signaling protein sorting
The Na+/K+ -ATPase pump is considered a(n) ______ because it binds both Na+ and K+ and transports them in opposite directions.
antiporter
The transporter protein that binds two or more ions or molecules and moves them in opposite directions is called a(n)
antiporter
In adherens junctions, proteins called ___________ connect cells to each other. In the cytosol, adherens junctions bind to _____________ filaments.
cadherins, actin
Cell adhesion molecules (CAMs) include the two integral membrane proteins
cadherins, integrins
The binding of cadherin proteins in adjacent cells requires the presence of ___________ ions to change the conformation of the cadherin proteins.
calcium
A key component of anchoring junctions are proteins called CAMs, which stands for
cell adhesion molecules
The anchoring junction proteins that form the connections between cells are called:
cell adhesion molecules
In multicellular animals, cells are linked to one another by
cell junctions
Transmembrane proteins called _________ proteins allow ions and hydrophilic molecules to cross the phospholipid bilayer.
channel
What is the short, rigid molecule produced by animal cells that is involved in membrane fluidity?
cholesterol
The membrane proteins that form tight junctions are called
claudin, occludin
Plant cells can prevent the loss of water and nutrients from wounds by
closing their plasmodesmata
A key similarity between simple and facilitated diffusion is that both require
concentration gradients.
In vertebrates, six _______________ proteins form a connexon of a gap junction.
connexin
What process requires gap junctions?
contraction of cardiac cell muscles
Functions of tight junctions include all the following except:
exchanging ions and small molecules between cells
Vesicular movement of large molecules into cells is called ___________________ , and vesicular movement of large molecules out of cells is called _______________
exocytosis, endocytosis
The leaflet of the plasma membrane that faces the outside of the cell is called the _____________ leaflet.
extracellular
A cell contains less sodium than the surrounding environment. What type of transport is required to import sodium ions into the cell?
facilitated diffusion
In the Agre experiment, the observation that the frog oocytes injected with CHIP 28 mRNA swelled and burst led scientists to conclude that the protein encoded by CHIP28 allows
facilitated diffusion of water.
True or false: The two leaflets of the plasma membrane have the same lipid composition
false
True or false: Lipid rafts have the same lipid composition as the rest of the plasma membrane
false -- Lipid rafts have a different composition than the surrounding membrane. They usually contain more cholesterol and unique sets of lipid-anchored proteins and transmembrane proteins.
In animals, _________ junctions form channels between cells that allow cells to communicate with one another.
gap
Lipids are moved from one leaflet to another by the enzyme ___________, which requires energy input in the form of __________.
flippase, ATP
Some molecules are known to move laterally in the plane of the membrane. As such, we can say the membrane is
fluid
According to the ______ model, membrane proteins and lipids are able to move relative to one another within the plasma membrane.
fluid-mosaic
What property of biological membranes describes the ability of individual molecules to move within the membrane?
fluidity
What type of cell junction connects cells to the extracellular matrix via integrins and binds to actin filaments in the cytosol?
focal adhesion
Small molecules and ions can pass through the connexons of
gap junctions
The function of plasmodesmata is most similar to that of ______ in animal cells.
gap junctions
When channel proteins are _________, it means they can open and close to regulate the movement of ions and molecules across the cell membrane.
gated
When the concentration of a solute is higher on one side of membrane than the other, a(n) transmembrane ________ is established.
gradient
Select the types of anchoring junctions found in animals.
hemidesmosomes focal adhesions adherens junctions desmosomes
The four types of anchoring junctions in humans are adherens junctions, desmosomes, _________________ and _____________ adherons.
hemidesmosomes, focal
The two types of anchoring junctions that connect cells to the extracellular matrix are
hemidesmosomes, focal adhesions
Select the interactions that are typically involved in peripheral proteins binding to biological membranes.
hydrogen and ionic bonds
Peripheral membrane proteins can be removed from integral proteins by changing the pH or salt concentration because they are bound to integral proteins by which types of bonds?
hydrogen or ionic bonds
Transmembrane proteins do not flip flop across bilayer leaflets because
hydrophilic protein regions would pass through the hydrophobic bilayer interior.
In ________ solutions, animal cells will take up water. In extreme cases, the cells can rupture in a process called osmotic lysis.
hypotonic
When the concentration of solutes outside the cell is lower than that intra-cellularly, the solution is said to be __________ relative to the inside of the cell.
hypotonic
Water diffuses through a membrane from a solution that is ______________ (lower concentration of dissolved particles) into a solution that is _____________ (higher concentration of dissolved particles). Solutions with identical concentrations are said to be _______________.
hypotonic, hypertonic, isotonic
A sample of cells is placed in a salt solution. The cells subsequently shrink and the membrane deforms. Relative to the cells, the salt solution is:
hyptertonic
A solution whose solute concentration is higher than the concentration of solutes inside a cell is Multiple choice question.
hyptertonic
A membrane protein that has a portion integrated into the hydrophobic region of the membrane is called a(n) ______ membrane protein
integral
Anchoring junctions that create connections between cells and the extracellular matrix contain proteins called
integrins
Hemidesmosomes connect cells to the extracellular matrix via
integrins
The metastasis (or spread) of cancer cells can be associated with abnormalities in
integrins
_____________ are cell-surface receptor proteins that create connections between cells and the extracellular matrix and do not require Ca2+ to function.
integrins
In focal adhesions, cells are connected to the extracellular matrix via proteins called ______________. In the cytosol, focal adhesions bind to ____________ filaments.
integrins, actin
Which of the following statements regarding hemidesmosomes are true?
interact with intermediate filaments in the cytosol contain integrins interact with the extracellular matrix
Passage of ______ through gap junctions allows the coordinated contraction of cardiac muscle cells.
ions
Passage of ___________ through gap junctions allows the coordinated contraction of cardiac muscle cells.
ions
Cell _____________ are specialized structures within multicellular animals that physically adhere cells to each other.
junctions
Researchers discovered that certain cell types allow water to move across the plasma membrane faster than would occur with simple diffusion. Which of the following are such cell types?
kidney bladder red blood cells
The double bonds in unsaturated lipids create ______ in the nonpolar tails, making it more difficult for neighboring lipids to interact.
kinks
Which of the following movements of a phospholipid are energetically favorable within the bilayer?
lateral movements rotational movements
Most phospholipids move freely within a semifluid membrane
laterally along the plane of the membrane in two dimensions
At a high temperature, cholesterol makes a membrane ______ fluid.
less
Proteins that associate with a membrane because they have a lipid molecule that is covalently attached to a side chain with the protein are called
lipid-anchored proteins
Which of the following proteins are integral membrane proteins
lipid-anchored proteins transmembrane proteins
The cell membrane is referred to as a mosaic because it is a mixture of what types of molecules?
lipids proteins carbohydrates
Plasmodesmata can close to prevent
loss of water and nutrients
In osmosis, water moves from areas of
low solute concentration to areas of high solute concentration.
Osmosis describes the movement of water from areas where the solute concentration is ____________ to areas in which the solute concentration is _________.
lower, higher
What are functions of the selectively permeable plasma membrane?
maintain a proper supply of essential molecules such as glucose and amino acids maintain a proper balance of ions within the cell remove waste products from within the cell
Abnormalities in integrins are often associated with
metastasis of cancer cells.
Integral membrane proteins have transmembrane segments that are ______ and interact with the ______ of the phospholipid bilayer.
nonpolar; hydrophobic tails
The fatty acid tails of phospholipids are ______ and are found in the ______ of the phospholipid bilayer.
nonpolar; interior
The movement of charged ions through the Na+/K+ -ATPase pump creates a net charge difference because
one cycle of pumping results in the net export of one positive charge.
Some freshwater microorganisms that live in hypotonic environments use a contractile vacuole to help prevent
osmotic lysis
Proteins that associate with the plasma membrane through non-covalent interactions with phospholipids or transmembrane proteins are called ____________ membrane proteins.
peripheral
The selective _______________ of the plasma membrane allows the cell to maintain a favorable internal environment.
permeability
Which process is most appropriate if a cell needs to engulf and kill a large bacterium via vesicle formation?
phagocytosis
Which of the following are examples of endocytosis?
phagocytosis receptor-mediated endocytosis pinocytosis
What are the three molecular components of cellular membranes?
phospholipids proteins carbohydrates
The three main types of macromolecules that comprise the plasma membrane are
phospholipids, proteins, carbohydrates
Major changes in cell size arising from the effects of osmosis are limited in plants because
plant cells have a cell wall that limits plasma membrane expansion in a hypotonic environment.
In a plasmodesma, the ______ of one cell is continuous with that of another cell.
plasma membrane
What separates the internal contents of a cell from the extracellular environment?
plasma membrane
______________ ____________ are involved in many different cellular functions, including cell compartmentalization and the selective uptake of ions and molecules.
plasma membrane
The _____________ of plant cells are functionally similar to gap junctions in animal cells because they allow passage of ions and molecules between the cytosol of adjacent plant cells.
plasmodesmata
The intercellular channels that connect plant cells to one another are called
plasmodesmata
What type of cell junctions form channels between adjacent plant cells?
plasmodesmata
Phospholipids have a ____________ head region that will interact with aqueous environments.
polar
"Flip-flop" movement of __________ head groups on phospholipids through ___________ interiors of leaflets is energetically unfavorable.
polar, hydrophobic
______ active transport involves a pump that uses energy from ATP to transport solutes against a gradient.
primary
Which of the following types of transport involves pumping ions against a gradient using ATP as a source of energy?
primary active transport
Cholesterol is brought into the cell via:
receptor-mediated endocytosis
The three types of endocytosis are
receptor-mediated endocytosis,, phagocytosis, and pinocytosis
What type of transport uses a pre-existing gradient to drive the transport of another molecule?
secondary active transport
All cells are surrounded by a ______________ permeable plasma membrane, meaning that the membrane allows the passage of some molecules and ions but not others.
selectively
The plasma membrane of a cell is considered to be
selectively permeable.
The fluidity of the plasma membrane can be increased by incorporating fatty acids with ______ tails or by incorporating ______ lipids.
shorter ; unsaturated
The fluidity of the plasma membrane can be increased by incorporating fatty acids with ______ tails or by incorporating ______ lipids
shorter, unsaturated
When a gap junction forms, a total of _________ connexin proteins in one cell form a connexon that aligns with a connexon in an adjacent cell.
six
What organelle in adjacent cells is connected by the central tubules in plasmodesmata?
smooth endoplasmic reticulum
Due to the Na+/K+ -ATPase, cells are able to maintain concentration gradients so that the concentration of _____________ ions is greater outside the cell than inside, and the concentration of ____________ ions is greater inside the cell than outside.
sodium, potassium
Water is considered to be a ______ that dissolves ______ molecules.
solvent, solute
Transmembrane proteins are able to span the hydrophobic portion of the bilayer because they have
stretches of nonpolar amino acids.
The Na+/K+-ATPase pump is considered to be electrogenic. This is because
the actions of the pump create an electrical gradient.
The primary difference between endocytosis and exocytosis is
the direction of transport
Cells use electrochemical gradients for which of the following functions?
the export of cellular wastes ATP synthesis in the chloroplast and mitochondria the contraction of muscle fibers nutrient uptake
"Flip flop" movements of phospholipids within the membrane are unfavorable because
the polar head groups of phospholipids have to traverse the hydrophobic interior of the membrane.
Cellular membranes are described as fluid because
their lipids and proteins can move relative to each other.
Which of the following statements about plasmodesmata is true?
they can be open, closed or dilated
What is the function of cadherins?
they create cell to cell junctions
Tight junctions are not mechanically strong because
they do not have strong connections with the cytoskeleton.
The Na+/K+ -ATPase hydrolyzes ATP after the binding of:
three Na+
Which of the following are pumped by the Na+/K+ -ATPase?
three Na+ out of the cell two K+ into the cell
In animals, cell junctions called ____________ junctions form a seal between adjacent cells to prevent leakage of material.
tight
One function of _____________ junctions between intestinal cells is the prevention of leakage of materials from the lumen of the intestine into the blood, and vice versa.
tight
What type of cell junction is made of membrane proteins called occludin and claudin that form interlaced strands in the plasma membrane?
tight function
Which of the following cell junctions prevent material from passing between adjacent cells of animals?
tight junctions
True or false: Cadherins and integrins play roles in cell communication.
true
True or false: Plant cells can change the diameter of the plasmodesmata channels.
true (can be dilated)
Which of the following are functions of transporter proteins?
uptake of hormones into animal cells uptake of amino acids and sugars into cells export of wastes from the cell
During exocytosis, a protein-coated __________ loaded with cargo is released from the _____________ apparatus, and then fuses with the ____________ ____________.
vesicle, Golgi, plasma membrane
