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Structure and
Function of
Plasma
Membranes
Components and Structure
Passive Transport
Active Transport
Bulk Transport
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Structure and Function of Plasma Membranes > Components and Structure
Components and Structure
• Introduction
• Fluid Mosaic Model
• Membrane Fluidity
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Structure and Function of Plasma Membranes > Components and Structure
Introduction
• The plasma membrane allows cells to block, take in, and excrete substances, all
in controlled quantities.
• The plasma membrane is very flexible in order to allow certain cells, such as red
blood cells and white blood cells, to change shape as they pass through narrow
capillaries.
• The plasma membrane carries markers that allow cells to recognize one another.
• The plasma membrane has the ability to transmit signals via receptors.
• The principal components of a plasma membrane are lipids (phospholipids and
cholesterol), proteins, and carbohydrates.
Plasma Membranes Analogous to Grand Central
Station
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Structure and Function of Plasma Membranes > Components and Structure
Fluid Mosaic Model
• The main fabric of the membrane is composed of amphiphilic or dual-loving,
phospholipid molecules.
• Integral proteins, the second major component of plasma membranes, are
integrated completely into the membrane structure with their hydrophobic
membrane-spanning regions interacting with the hydrophobic region of the
phospholipid bilayer.
• Carbohydrates, the third major component of plasma membranes, are always
found on the exterior surface of cells where they are bound either to proteins
(forming glycoproteins) or to lipids (forming glycolipids).
The Components and functions of the Plasma
Membrane
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Structure and Function of Plasma Membranes > Components and Structure
Membrane Fluidity
• The membrane is fluid but also fairly rigid and can burst if penetrated or if a cell
takes in too much water.
• The mosaic nature of the plasma membrane allows a very fine needle to easily
penetrate it without causing it to burst and allows it to self-seal when the needle is
extracted.
• If saturated fatty acids are compressed by decreasing temperatures, they press in
on each other, making a dense and fairly rigid membrane.
• If unsaturated fatty acids are compressed, the "kinks" in their tails push adjacent
phospholipid molecules away, which helps maintain fluidity in the membrane.
• The ratio of saturated and unsaturated fatty acids determines the fluidity in the
Membrane Fluidity
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membrane at cold temperatures.
• Cholesterol functions as a buffer, preventing lower temperatures from inhibiting
fluidity and preventing higher temperatures from increasing fluidity.
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Structure and Function of Plasma Membranes > Passive Transport
Passive Transport
• Introduction
• Selective Permeability
• Diffusion
• Facilitated transport
• Osmosis
• Tonicity
• Tonicity in Living Systems
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Structure and Function of Plasma Membranes > Passive Transport
Introduction
• Plasma membranes are selectively permeable; if they were to lose this selectivity,
the cell would no longer be able to sustain itself.
• In passive transport, substances simply move from an area of higher
concentration to an area of lower concentration, which does not require the input
of energy.
• Concentration gradient, size of the particles that are diffusing, and temperature of
the system affect the rate of diffusion.
• Some materials diffuse readily through the membrane, but others require
specialized proteins, such as channels and transporters, to carry them into or out
Passive Transport
of the cell.
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Structure and Function of Plasma Membranes > Passive Transport
Selective Permeability
• The interior and exterior surfaces of the plasma membrane are not identical,
which adds to the selective permeability of the membrane.
• Fat soluble substances are able to pass easily to the hydrophobic interior of the
plasma membrane and diffuse into the cell.
• Polar molecules and charged molecules do not diffuse easily through the lipid
core of the plasma membrane and must be transported across by proteins,
sugars, or amino acids.
Asymmetry in Plasma Membranes
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Structure and Function of Plasma Membranes > Passive Transport
Diffusion
• Substances diffuse according to their concentration gradient; within a system,
different substances in the medium will each diffuse at different rates according to
their individual gradients.
• After a substance has diffused completely through a space, removing its
concentration gradient, molecules will still move around in the space, but there will
be no net movement of the number of molecules from one area to another, a
state known as dynamic equilibrium.
• Several factors affect the rate of diffusion of a solute including the mass of the
solute, the temperature of the environment, the solvent density, and the distance
traveled.
Diffusion
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Structure and Function of Plasma Membranes > Passive Transport
Facilitated transport
• A concentration gradient exists that would allow ions and polar molecules to
diffuse into the cell, but these materials are repelled by the hydrophobic parts of
the cell membrane.
• Facilitated diffusion uses integral membrane proteins to move polar or charged
substances across the hydrophobic regions of the membrane.
• Channel proteins can aid in the facilitated diffusion of substances by forming a
hydrophilic passage through the plasma membrane through which polar and
charged substances can pass.
• Channel proteins can be open at all times, constantly allowing a particular
substance into or out of the cell, depending on the concentration gradient; or they
Channel Proteins in Facilitated Transport
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can be gated and can only be opened by a particular biological signal.
• Carrier proteins aid in facilitated diffusion by binding a particular substance, then
altering their shape to bring that substance into or out of the cell.
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Structure and Function of Plasma Membranes > Passive Transport
Osmosis
• Osmosis occurs according to the concentration gradient of water across the
membrane, which is inversely proportional to the concentration of solutes.
• Osmosis occurs until the concentration gradient of water goes to zero or until the
hydrostatic pressure of the water balances the osmotic pressure.
• Osmosis occurs when there is a concentration gradient of a solute within a
solution, but the membrane does not allow diffusion of the solute.
Osmosis
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Structure and Function of Plasma Membranes > Passive Transport
Tonicity
• Osmolarity describes the total solute concentration of a solution; solutions with a
low solute concentration have a low osmolarity, while those with a high osmolarity
have a high solute concentration.
• Water moves from the side of the membrane with lower osmolarity (and more
water) to the side with higher osmolarity (and less water).
• In a hypotonic solution, the extracellular fluid has a lower osmolarity than the fluid
inside the cell; water enters the cell.
• In a hypertonic solution, the extracellular fluid has a higher osmolarity than the
fluid inside the cell; water leaves the cell.
• In an isotonic solution, the extracellular fluid has the same osmolarity as the cell;
Changes in Cell Shape Due to Dissolved Solutes
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there will be no net movement of water into or out of the cell.
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Structure and Function of Plasma Membranes > Passive Transport
Tonicity in Living Systems
• In a hypotonic environment, water enters a cell, causing it to swell and burst
(lyse).
• In a hypertonic environment, water leaves a cell, causing it to shrink and die.
• In plants, in a hypotonic environment, the inflow of water produces turgor
pressure, which stiffens the cell walls of the plant, while in a hypertonic
environment, turgor pressure is lost, and the plant wilts.
• Some protists that lack cell walls have contractile vacuoles, which collect excess
water from the cell and pump it out, keeping the cell from lysing.
• Freshwater fish living in a hypotonic environment take in salt through their gills
and excrete diluted urine to rid themselves of excess water; saltwater fish living in
Turgor Pressure and Tonicity in a Plant Cell
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a hypertonic environment secrete salt through their gills and excrete highly
concentrated urine.
• In vertebrates, osmoreceptors monitor the concentration of solutes in the blood,
and albumin controls osmotic pressure in tissues.
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Structure and Function of Plasma Membranes > Active Transport
Active Transport
• Electrochemical Gradient
• Primary Active Transport
• Secondary Active Transport (Co-transport)
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Structure and Function of Plasma Membranes > Active Transport
Electrochemical Gradient
• The electrical and concentration gradients of a membrane tend to drive sodium
into and potassium out of the cell, and active transport works against these
gradients.
• To move substances against a concentration or electrochemical gradient, the cell
must utilize energy in the form of ATP during active transport.
• Primary active transport, which is directly dependent on ATP, moves ions across
a membrane and creates a difference in charge across that membrane.
• Secondary active transport, created by primary active transport, is the transport of
a solute in the direction of its electrochemical gradient and does not directly
Electrochemical Gradient
require ATP.
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• Carrier proteins such as uniporters, symporters, and antiporters perform primary
active transport and facilitate the movement of solutes across the cell's
membrane.
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Structure and Function of Plasma Membranes > Active Transport
Primary Active Transport
• The sodium-potassium pump moves K+ into the cell while moving Na+ at a ratio
of three Na+ for every two K+ ions.
• When the sodium-potassium-ATPase enzyme points into the cell, it has a high
affinity for sodium ions and binds three of them, hydrolyzing ATP and changing
shape.
• As the enzyme changes shape, it reorients itself towards the outside of the cell,
and the three sodium ions are released.
• The enzyme's new shape allows two potassium to bind and the phosphate group
to detach, and the carrier protein repositions itself towards the interior of the cell.
• The enzyme changes shape again, releasing the potassium ions into the cell.
Active Transport of Sodium and Potassium
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• After potassium is released into the cell, the enzyme binds three sodium ions,
which starts the process over again.
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Structure and Function of Plasma Membranes > Active Transport
Secondary Active Transport (Co-transport)
• While secondary active transport consumes ATP to generate the gradient down
which a molecule is moved, the energy is not directly used to move the molecule
across the membrane.
• Both antiporters and symporters are used in secondary active transport.
• Secondary active transport brings sodium ions into the cell, and as sodium ion
concentrations build outside the plasma membrane, an electrochemical gradient
is created.
• If a channel protein is open via primary active transport, the ions will be pulled
through the membrane along with other substances that can attach themselves to
Secondary Active Transport
the transport protein through the membrane.
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• Secondary active transport is used to store high-energy hydrogen ions in the
mitochondria of plant and animal cells for the production of ATP.
• The potential energy in the hydrogen ions is translated into kinetic energy as the
ions surge through the channel protein ATP synthase, and that energy is used to
convert ADP into ATP.
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Structure and Function of Plasma Membranes > Bulk Transport
Bulk Transport
• Endocytosis
• Exocytosis
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Structure and Function of Plasma Membranes > Bulk Transport
Endocytosis
• Endocytosis consists of phagocytosis, pinocytosis, and receptor-mediated
endocytosis.
• Endocytosis takes particles into the cell that are too large to passively cross the
cell membrane.
• Phagocytosis is the taking in of large food particles, while pinocytosis takes in
liquid particles.
• Receptor-mediated endocytosis uses special receptor proteins to help carry large
particles across the cell membrane.
Phagocytosis
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Structure and Function of Plasma Membranes > Bulk Transport
Exocytosis
• Exocytosis is the opposite of endocytosis as it involves releasing materials from
the cell.
• Exocytosis has five stages, each leading up to the vesicle binding with the cell
membrane.
• Many bodily functions include the use of exocytosis, such as the release of
neurotransmitters into the synaptic cleft and the release of enzymes into the
blood.
Exocytosis
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Appendix
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Structure and Function of Plasma Membranes
Key terms
• active transport movement of a substance across a cell membrane against its concentration gradient (from low to high
concentration) facilitated by ATP conversion
• adenosine triphosphate a multifunctional nucleoside triphosphate used in cells as a coenzyme, often called the "molecular unit
of energy currency" in intracellular energy transfer
• amphiphilic Having one surface consisting of hydrophilic amino acids and the opposite surface consisting of hydrophobic (or
lipophilic) ones.
• amphiphilic Having one surface consisting of hydrophilic amino acids and the opposite surface consisting of hydrophobic (or
lipophilic) ones.
• concentration gradient A concentration gradient is present when a membrane separates two different concentrations of
molecules.
• concentration gradient A concentration gradient is present when a membrane separates two different concentrations of
molecules.
• diffusion The passive movement of a solute across a permeable membrane
• electrochemical gradient The difference in charge and chemical concentration across a membrane.
• electrogenic pump An ion pump that generates a net charge flow as a result of its activity.
• endosome An endocytic vacuole through which molecules internalized during endocytosis pass en route to lysosomes
• facilitated diffusion The spontaneous passage of molecules or ions across a biological membrane passing through specific
transmembrane integral proteins.
• fluidity A measure of the extent to which something is fluid.The reciprocal of its viscosity.
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Structure and Function of Plasma Membranes
• hydrophilic Having an affinity for water; able to absorb, or be wetted by water, "water-loving."
• hydrophobic Lacking an affinity for water; unable to absorb, or be wetted by water, "water-fearing."
• hypertonic having a greater osmotic pressure than another
• hypertonic having a greater osmotic pressure than another
• hypotonic Having a lower osmotic pressure than another; a cell in this environment causes water to enter the cell, causing it to
swell.
• hypotonic Having a lower osmotic pressure than another; a cell in this environment causes water to enter the cell, causing it to
swell.
• isotonic having the same osmotic pressure
• membrane protein Proteins that are attached to, or associated with the membrane of a cell or an organelle.
• Na+-K+ ATPase An enzyme located in the plasma membrane of all animal cells that pumps sodium out of cells while pumping
potassium into cells.
• neutrophil A cell, especially a white blood cell that consumes foreign invaders in the blood.
• osmolarity The osmotic concentration of a solution, normally expressed as osmoles of solute per litre of solution.
• osmoregulation the homeostatic regulation of osmotic pressure in the body in order to maintain a constant water content
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Structure and Function of Plasma Membranes
• osmosis The net movement of solvent molecules from a region of high solvent potential to a region of lower solvent potential
through a partially permeable membrane
• passive transport A movement of biochemicals and other atomic or molecular substances across membranes that does not
require an input of chemical energy.
• permeable Of or relating to substance, substrate, membrane or material that absorbs or allows the passage of fluids.
• phospholipid Any lipid consisting of a diglyceride combined with a phosphate group and a simple organic molecule such as
choline or ethanolamine; they are important constituents of biological membranes
• plasma membrane The semipermeable membrane that surrounds the cytoplasm of a cell.
• polar a separation of electric charge leading to a molecule or its chemical groups having an electric dipole
• receptor a protein on a cell wall that binds with specific molecules so that they can be absorbed into the cell in order to control
certain functions
• secondary active transport A method of transport in which the electrochemical potential difference created by pumping ions out
of the cell is used to transport molecules across a membrane.
• secretion The act of secreting (producing and discharging) a substance, especially from a gland.
• semipermeable membrane A type of biological membrane that will allow certain molecules or ions to pass through it by diffusion
and occasionally by specialized facilitated diffusion
• solute Any substance that is dissolved in a liquid solvent to create a solution
• vesicle A membrane-bound compartment found in a cell.
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Structure and Function of Plasma Membranes
Turgor Pressure and Tonicity in a Plant Cell
The turgor pressure within a plant cell depends on the tonicity of the solution in which it is bathed.
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Structure and Function of Plasma Membranes
Phospholipid aggregation
In an aqueous solution, phospholipids tend to arrange themselves with their polar heads facing outward and their hydrophobic tails facing inward.
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Structure and Function of Plasma Membranes
Uniporters, Symporters, and Antiporters
A uniporter carries one molecule or ion.A symporter carries two different molecules or ions, both in the same direction.An antiporter also carries two
different molecules or ions, but in different directions.
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Structure and Function of Plasma Membranes
Passive Transport
Diffusion is a type of passive transport.Diffusion through a permeable membrane moves a substance from an area of high concentration (extracellular
fluid, in this case) down its concentration gradient (into the cytoplasm).
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Structure and Function of Plasma Membranes
Receptor-Mediated Endocytosis
In receptor-mediated endocytosis, uptake of substances by the cell is targeted to a single type of substance that binds to the receptor on the external
surface of the cell membrane.
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Structure and Function of Plasma Membranes
Pinocytosis
In pinocytosis, the cell membrane invaginates, surrounds a small volume of fluid, and pinches off.
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Structure and Function of Plasma Membranes
The structure of a phospholipid molecule
This phospholipid molecule is composed of a hydrophilic head and two hydrophobic tails.The hydrophilic head group consists of a phosphate-containing
group attached to a glycerol molecule.The hydrophobic tails, each containing either a saturated or an unsaturated fatty acid, are long hydrocarbon
chains.
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Structure and Function of Plasma Membranes
Channel Proteins in Facilitated Transport
Facilitated transport moves substances down their concentration gradients.They may cross the plasma membrane with the aid of channel proteins.
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Structure and Function of Plasma Membranes
Carrier Proteins
Some substances are able to move down their concentration gradient across the plasma membrane with the aid of carrier proteins.Carrier proteins
change shape as they move molecules across the membrane.
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Structure and Function of Plasma Membranes
Turgor Pressure and Plasmolysis
Without adequate water, the plant on the left has lost turgor pressure, visible in its wilting; the turgor pressure is restored by watering it (right).
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Structure and Function of Plasma Membranes
Diffusion
Diffusion through a permeable membrane moves a substance from an area of high concentration (extracellular fluid, in this case) down its concentration
gradient (into the cytoplasm).
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Structure and Function of Plasma Membranes
Membrane Fluidity
The plasma membrane is a fluid combination of phospholipids, cholesterol, and proteins.Carbohydrates attached to lipids (glycolipids) and to proteins
(glycoproteins) extend from the outward-facing surface of the membrane.
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Structure and Function of Plasma Membranes
Contractile Vacuoles
A paramecium's contractile vacuole, here visualized using bright field light microscopy at 480x magnification, continuously pumps water out of the
organism's body to keep it from bursting in a hypotonic medium.
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Structure and Function of Plasma Membranes
The fluid mosaic model of the plasma membrane
The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and
proteins.Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward-facing surface of the membrane.
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Structure and Function of Plasma Membranes
Structure of integral membrane proteins
Integral membrane proteins may have one or more alpha-helices that span the membrane (examples 1 and 2), or they may have beta-sheets that span
the membrane (example 3).
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Structure and Function of Plasma Membranes
Phagocytosis
In phagocytosis, the cell membrane surrounds the particle and engulfs it.
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Structure and Function of Plasma Membranes
Electrochemical Gradient
Electrochemical gradients arise from the combined effects of concentration gradients and electrical gradients.
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Structure and Function of Plasma Membranes
Exocytosis
In exocytosis, vesicles containing substances fuse with the plasma membrane.The contents are then released to the exterior of the cell.
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Structure and Function of Plasma Membranes
Plasma Membranes Analogous to Grand Central Station
Despite its seeming hustle and bustle, Grand Central Station functions with a high level of organization.People and objects move from one location to
another, they cross or are contained within certain boundaries, and they provide a constant flow as part of larger activity.Analogously, a plasma
membrane's functions involve movement within the cell and across boundaries in the process of intracellular and intercellular activities.
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Structure and Function of Plasma Membranes
Secondary Active Transport
An electrochemical gradient, created by primary active transport, can move other substances against their concentration gradients, a process called cotransport or secondary active transport.
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Structure and Function of Plasma Membranes
The Components and functions of the Plasma Membrane
The principal components of a plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates attached to some of the lipids
and some of the proteins.
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Structure and Function of Plasma Membranes
Active Transport of Sodium and Potassium
Primary active transport moves ions across a membrane, creating an electrochemical gradient (electrogenic transport).
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Structure and Function of Plasma Membranes
Asymmetry in Plasma Membranes
The exterior surface of the plasma membrane is not identical to the interior surface of the same membrane.
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Structure and Function of Plasma Membranes
Osmosis
In osmosis, water always moves from an area of higher water concentration to one of lower concentration.In the diagram shown, the solute cannot pass
through the selectively permeable membrane, but the water can.
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Structure and Function of Plasma Membranes
Changes in Cell Shape Due to Dissolved Solutes
Osmotic pressure changes the shape of red blood cells in hypertonic, isotonic, and hypotonic solutions.
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Structure and Function of Plasma Membranes
Which of the following attributes most accurately describes
plasma membranes?
A) inhibit integral protein attachment
B) provide very flexible cell borders
C) made exclusively from lipids
D) are the same in all cells
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Structure and Function of Plasma Membranes
Which of the following attributes most accurately describes
plasma membranes?
A) inhibit integral protein attachment
B) provide very flexible cell borders
C) made exclusively from lipids
D) are the same in all cells
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Structure and Function of Plasma Membranes
Which of the following statements best describes the lipid bilayer
plasma membrane?
A) The interior and exterior surfaces of the membrane are hydrophilic and
the middle is hydrophobic
B) The interior and exterior surfaces of the membrane are hydrophobic
and the middle is hydrophilic
C) The interior surface and the middle of the membrane are hydrophobic
and the exterior is hydrophilic
D) The exterior surface and the middle of the membrane are hydrophobic
and the interior is hydrophilic
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Structure and Function of Plasma Membranes
Which of the following statements best describes the lipid bilayer
plasma membrane?
A) The interior and exterior surfaces of the membrane are hydrophilic and
the middle is hydrophobic
B) The interior and exterior surfaces of the membrane are hydrophobic
and the middle is hydrophilic
C) The interior surface and the middle of the membrane are hydrophobic
and the exterior is hydrophilic
D) The exterior surface and the middle of the membrane are hydrophobic
and the interior is hydrophilic
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Structure and Function of Plasma Membranes
What does the term 'mosaic' refer to in the fluid mosaic model of
the plasma membrane?
A) The array of colors seen when the plasma membrane is viewed with a
microscope
B) That scientists had to put together pieces from various models to
make one to fit
C) The different sizes of plasma membranes that exist in nature
D) The heterogeneous composition of phospholipids, cholesterol,
proteins, and carbohydrates
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Structure and Function of Plasma Membranes
What does the term 'mosaic' refer to in the fluid mosaic model of
the plasma membrane?
A) The array of colors seen when the plasma membrane is viewed with a
microscope
B) That scientists had to put together pieces from various models to
make one to fit
C) The different sizes of plasma membranes that exist in nature
D) The heterogeneous composition of phospholipids, cholesterol,
proteins, and carbohydrates
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Structure and Function of Plasma Membranes
What role does cholesterol play in plasma membrane fluidity?
A) Cholesterol has a detrimental role in membrane fluidity.
B) Cholesterol acts like a magnet pulling proteins around the membrane.
C) Cholesterol forces out the unsaturated fatty acids that 'kink' from the
membrane.
D) Cholesterol extends the range of temperature in which the membrane
is fluid and functional.
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Structure and Function of Plasma Membranes
What role does cholesterol play in plasma membrane fluidity?
A) Cholesterol has a detrimental role in membrane fluidity.
B) Cholesterol acts like a magnet pulling proteins around the membrane.
C) Cholesterol forces out the unsaturated fatty acids that 'kink' from the
membrane.
D) Cholesterol extends the range of temperature in which the membrane
is fluid and functional.
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Structure and Function of Plasma Membranes
Which of the following statements about passive transport is true?
A) Membrane proteins are always needed in order for it to take place.
B) Substances move from areas of low concentration to areas of high
concentration.
C) The input of ATP is required in order to facilitate transportation.
D) Substances move from areas of high concentration to areas of low
concentration.
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Structure and Function of Plasma Membranes
Which of the following statements about passive transport is true?
A) Membrane proteins are always needed in order for it to take place.
B) Substances move from areas of low concentration to areas of high
concentration.
C) The input of ATP is required in order to facilitate transportation.
D) Substances move from areas of high concentration to areas of low
concentration.
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Structure and Function of Plasma Membranes
Which of the following substances will NOT diffuse easily across
the plasma membrane?
A) Vitamin K
B) Water
C) Oxygen
D) Sodium ions
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Structure and Function of Plasma Membranes
Which of the following substances will NOT diffuse easily across
the plasma membrane?
A) Vitamin K
B) Water
C) Oxygen
D) Sodium ions
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Structure and Function of Plasma Membranes
Which of the following factors does NOT affect the rate of diffusion
across a membrane?
A) the number of different types of particles in a solution
B) the temperature of a solution
C) the size of the diffusing particles
D) the concentration gradient across the cell membrane
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Structure and Function of Plasma Membranes
Which of the following factors does NOT affect the rate of diffusion
across a membrane?
A) the number of different types of particles in a solution
B) the temperature of a solution
C) the size of the diffusing particles
D) the concentration gradient across the cell membrane
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Structure and Function of Plasma Membranes
Which of the following characteristics distinguishes facilitated
transport from simple diffusion? Passive transport
______________.
A) requires the input of cellular energy to transport biomolecules.
B) uses membrane proteins and channels to move molecules down
concentration gradients.
C) describes the movement of biomolecules such as proteins,
carbohydrates, and fatty acids.
D) explains the movement of molecules or ions from high to low
concentration.
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Structure and Function of Plasma Membranes
Which of the following characteristics distinguishes facilitated
transport from simple diffusion? Passive transport
______________.
A) requires the input of cellular energy to transport biomolecules.
B) uses membrane proteins and channels to move molecules down
concentration gradients.
C) describes the movement of biomolecules such as proteins,
carbohydrates, and fatty acids.
D) explains the movement of molecules or ions from high to low
concentration.
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Structure and Function of Plasma Membranes
Which of the following statements about channel proteins is true?
A) Polar compounds pass through them to avoid nonpolar regions.
B) They change shape as they move molecules across a membrane.
C) All of them are open at all times to allow passage of materials.
D) all of these answers
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Structure and Function of Plasma Membranes
Which of the following statements about channel proteins is true?
A) Polar compounds pass through them to avoid nonpolar regions.
B) They change shape as they move molecules across a membrane.
C) All of them are open at all times to allow passage of materials.
D) all of these answers
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Structure and Function of Plasma Membranes
In a beaker separated by a membrane permeable only to water,
one area has a high solute concentration and the other has a low
solute concentration. What do you expect will happen in the
beaker?
A) Water will move to the area of low solute concentration.
B) Water will move to the area of high water concentration.
C) Water will move to the area of high solute concentration.
D) The solute will move to the area of low solute concentration.
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Structure and Function of Plasma Membranes
In a beaker separated by a membrane permeable only to water,
one area has a high solute concentration and the other has a low
solute concentration. What do you expect will happen in the
beaker?
A) Water will move to the area of low solute concentration.
B) Water will move to the area of high water concentration.
C) Water will move to the area of high solute concentration.
D) The solute will move to the area of low solute concentration.
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Structure and Function of Plasma Membranes
You take a sample of blood cells and place them in a solution.
Fifteen minutes later, you observe that they appear shriveled.
What is the tonicity of the solution they were placed in?
A) Hypotonic
B) Isotonic
C) Hypertonic
D) Equitonic
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Structure and Function of Plasma Membranes
You take a sample of blood cells and place them in a solution.
Fifteen minutes later, you observe that they appear shriveled.
What is the tonicity of the solution they were placed in?
A) Hypotonic
B) Isotonic
C) Hypertonic
D) Equitonic
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Structure and Function of Plasma Membranes
Which of the following is used as a method of osmoregulation in
humans?
A) albumin
B) plasmolysis
C) contractile vacuoles
D) turgor pressure
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Structure and Function of Plasma Membranes
Which of the following is used as a method of osmoregulation in
humans?
A) albumin
B) plasmolysis
C) contractile vacuoles
D) turgor pressure
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Structure and Function of Plasma Membranes
How does active transport move substances against the
electrochemical gradient?
A) Sodium and potassium help push substances across membranes.
B) ATP causes red blood cells to break down membranes.
C) all of these answers
D) With the help of ATP, pumps move substances across membranes
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Structure and Function of Plasma Membranes
How does active transport move substances against the
electrochemical gradient?
A) Sodium and potassium help push substances across membranes.
B) ATP causes red blood cells to break down membranes.
C) all of these answers
D) With the help of ATP, pumps move substances across membranes
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Structure and Function of Plasma Membranes
Which of the following describes the mechanism of the sodiumpotassium pump?
A) Potassium cannot attach to the enzyme until the sodium ions detach
from the enzyme.
B) Sodium and potassium ions bind to the enzyme at the same time, and
then sodium is released.
C) After ATP is hydrolyzed, the phosphate group attaches to the enzyme
before the sodium ions.
D) The process begins when potassium attaches to the enzyme, which
then hydrolyzes ATP.
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Structure and Function of Plasma Membranes
Which of the following describes the mechanism of the sodiumpotassium pump?
A) Potassium cannot attach to the enzyme until the sodium ions detach
from the enzyme.
B) Sodium and potassium ions bind to the enzyme at the same time, and
then sodium is released.
C) After ATP is hydrolyzed, the phosphate group attaches to the enzyme
before the sodium ions.
D) The process begins when potassium attaches to the enzyme, which
then hydrolyzes ATP.
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Structure and Function of Plasma Membranes
Which of the following applies to secondary active transport and
not primary active transport?
A) It only involves moving a molecule up its concentration gradient.
B) It utilizes only antiporter proteins.
C) It does not directly require energy from ATP.
D) It always involves moving a molecule into the cell.
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Structure and Function of Plasma Membranes
Which of the following applies to secondary active transport and
not primary active transport?
A) It only involves moving a molecule up its concentration gradient.
B) It utilizes only antiporter proteins.
C) It does not directly require energy from ATP.
D) It always involves moving a molecule into the cell.
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Structure and Function of Plasma Membranes
What is the difference between phagocytosis and pinocytosis?
A) Phagocytosis takes in large food particles, while pinocytosis takes in
liquid particles.
B) Phagocytosis takes in carbohydrates, while pinocytosis takes in lipids.
C) Phagocytosis takes in cations, while pinocytosis takes in anions
D) Phagocytosis takes in caveolin, while pinocytosis takes in clathrin.
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Structure and Function of Plasma Membranes
What is the difference between phagocytosis and pinocytosis?
A) Phagocytosis takes in large food particles, while pinocytosis takes in
liquid particles.
B) Phagocytosis takes in carbohydrates, while pinocytosis takes in lipids.
C) Phagocytosis takes in cations, while pinocytosis takes in anions
D) Phagocytosis takes in caveolin, while pinocytosis takes in clathrin.
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Structure and Function of Plasma Membranes
Which stage of exocytosis involves the connection and holding
together of the vesicle's membrane with that of the cell
membrane?
A) vesicle trafficking
B) vesicle tethering
C) vesicle docking
D) vesicle priming
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Structure and Function of Plasma Membranes
Which stage of exocytosis involves the connection and holding
together of the vesicle's membrane with that of the cell
membrane?
A) vesicle trafficking
B) vesicle tethering
C) vesicle docking
D) vesicle priming
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Structure and Function of Plasma Membranes
Attribution
• Connexions. "Components and Structure." CC BY 3.0 http://cnx.org/content/m44416/latest/#tab-ch05_01_01
• Connexions. "Introduction." CC BY 3.0 http://cnx.org/content/m44415/latest/?collection=col11448/latest
• Connexions. "Components and Structure." CC BY 3.0 http://cnx.org/content/m44416/latest/#tab-ch05_01_01
• Wiktionary. "receptor." CC BY-SA 3.0 http://en.wiktionary.org/wiki/receptor
• Wiktionary. "plasma membrane." CC BY-SA 3.0 http://en.wiktionary.org/wiki/plasma+membrane
• Connexions. "Components and Structure." CC BY 3.0 http://cnx.org/content/m44416/latest/#tab-ch05_01_01
• Connexions. "Components and Structure." CC BY 3.0 http://cnx.org/content/m44416/latest/?collection=col11448/latest
• Wiktionary. "hydrophobic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hydrophobic
• Wiktionary. "hydrophilic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hydrophilic
• Wiktionary. "amphiphilic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/amphiphilic
• Connexions. "Components and Structure." CC BY 3.0 http://cnx.org/content/m44416/latest/?collection=col11448/latest
• Wiktionary. "phospholipid." CC BY-SA 3.0 http://en.wiktionary.org/wiki/phospholipid
• Wiktionary. "fluidity." CC BY-SA 3.0 http://en.wiktionary.org/wiki/fluidity
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wikipedia. "concentration gradient." CC BY-SA 3.0 http://en.wikipedia.org/wiki/concentration%20gradient
• Wikipedia. "passive transport." CC BY-SA 3.0 http://en.wikipedia.org/wiki/passive%20transport
• Wiktionary. "permeable." CC BY-SA 3.0 http://en.wiktionary.org/wiki/permeable
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• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wiktionary. "polar." CC BY-SA 3.0 http://en.wiktionary.org/wiki/polar
• Wiktionary. "amphiphilic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/amphiphilic
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wikipedia. "concentration gradient." CC BY-SA 3.0 http://en.wikipedia.org/wiki/concentration%20gradient
• Boundless Learning. "Boundless." CC BY-SA 3.0 http://www.boundless.com//biology/definition/diffusion
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wikipedia. "membrane protein." CC BY-SA 3.0 http://en.wikipedia.org/wiki/membrane%20protein
• Wikipedia. "facilitated diffusion." CC BY-SA 3.0 http://en.wikipedia.org/wiki/facilitated%20diffusion
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wiktionary. "solute." CC BY-SA 3.0 http://en.wiktionary.org/wiki/solute
• Wiktionary. "osmosis." CC BY-SA 3.0 http://en.wiktionary.org/wiki/osmosis
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wiktionary. "isotonic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/isotonic
• Wiktionary. "hypertonic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hypertonic
• Wiktionary. "hypotonic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hypotonic
• Wiktionary. "osmolarity." CC BY-SA 3.0 http://en.wiktionary.org/wiki/osmolarity
• Connexions. "Passive Transport." CC BY 3.0 http://cnx.org/content/m44417/latest/?collection=col11448/latest
• Wiktionary. "osmoregulation." CC BY-SA 3.0 http://en.wiktionary.org/wiki/osmoregulation
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• Wiktionary. "hypertonic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hypertonic
• Wiktionary. "hypotonic." CC BY-SA 3.0 http://en.wiktionary.org/wiki/hypotonic
• Wiktionary. "tonicity." CC BY-SA http://en.wiktionary.org/wiki/tonicity
• Connexions. "Active Transport." CC BY 3.0 http://cnx.org/content/m44418/latest/?collection=col11448/latest
• Wikipedia. "electrochemical gradient." CC BY-SA 3.0 http://en.wikipedia.org/wiki/electrochemical%20gradient
• Wikipedia. "active transport." CC BY-SA 3.0 http://en.wikipedia.org/wiki/active%20transport
• Wikipedia. "adenosine triphosphate." CC BY-SA 3.0 http://en.wikipedia.org/wiki/adenosine%20triphosphate
• Connexions. "Active Transport." CC BY 3.0 http://cnx.org/content/m44418/latest/?collection=col11448/latest
• Boundless Learning. "Boundless." CC BY-SA 3.0 http://www.boundless.com//biology/definition/electrogenic-pump
• Wikipedia. "Na -K ATPase." CC BY-SA 3.0 http://en.wikipedia.org/wiki/Na%20-K%20%20ATPase
• Wikibooks. "Structural Biochemistry/Membrane Proteins." CC BY-SA 3.0
http://en.wikibooks.org/wiki/Structural_Biochemistry/Membrane_Proteins#Secondary_Active_Transport
• Connexions. "Active Transport." CC BY 3.0 http://cnx.org/content/m44418/latest/?collection=col11448/latest
• Wikipedia. "secondary active transport." CC BY-SA 3.0 http://en.wikipedia.org/wiki/secondary%20active%20transport
• Connexions. "Bulk Transport." CC BY 3.0 http://cnx.org/content/m44419/latest/?collection=col11448/latest
• Wiktionary. "endosome." CC BY-SA 3.0 http://en.wiktionary.org/wiki/endosome
• Wiktionary. "neutrophil." CC BY-SA 3.0 http://en.wiktionary.org/wiki/neutrophil
• Connexions. "Bulk Transport." CC BY 3.0 http://cnx.org/content/m44419/latest/?collection=col11448/latest
• Wiktionary. "secretion." CC BY-SA 3.0 http://en.wiktionary.org/wiki/secretion
• Wiktionary. "vesicle." CC BY-SA 3.0 http://en.wiktionary.org/wiki/vesicle
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Structure and Function of Plasma Membranes
• Wikispaces. CC BY-SA http://epiehonorsbiology.wikispaces.com/Exocytosis
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