stabilization of the phospholipids
Cholesterol helps to stabilize the structure of the plasma membrane.
question
Identify Structure D.
answer
phospholipid bilayer of membrane
question
Identify Structure A.
answer
glycoprotein
Structure A is composed of both a carbohydrate and a protein.
question
Structure A in the figure is a(n) _____.
answer
transport protein
The protein is allowing solute molecules to enter the cell.
question
Which of these is hydrophobic like the interior of the plasma membrane?
answer
Lipid soluble molecules are hydrophobic.
question
Frequently, transplanted organs are rejected by the recipient's body. How is this reaction related to plasma membranes?
answer
Each person has a unique set of carbohydrate chains attached to his or her plasma membranes.
When cells with unrecognized carbohydrate chains are placed in a person, his or her immune system attacks the foreign cells as though they were infectious agents.
question
Overall, membranes seem to have a great deal in common, but on closer inspection it is revealed that membranes of different cells have unique properties. What is the primary component of membranes that gives membranes cell-specific properties?
answer
proteins
There is a large variety of proteins, and it is differences in these widely varying molecules that give a particular membrane its unique properties.
question
The lipids in a cell membrane are arranged _____.
answer
so that the nonpolar parts of two lipids point toward each other
A phospholipid bilayer can exist as a stable boundary between two aqueous compartments because the molecular arrangement shelters the hydrophobic tails of the phospholipids from water while exposing the hydrophilic heads to water.
question
The plasma membrane is selectively permeable. Which of the following can pass freely through the membrane with no assistance?
answer
oxygen and carbon dioxide
Oxygen and carbon dioxide, as well as other small, hydrophobic molecules, can move freely across the membrane.
question
In the figure below, working from the inside out, what would be the order of components observed?
answer
water, hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic head, water
Correct. The hydrophilic heads would orient themselves so that they are in contact with the aqueous surroundings, forming water bubbles, with the hydrophobic tails oriented toward each other.
question
In active transport,
answer
molecules move across the plasma membrane against their concentration gradient.
Molecules move against their concentration gradient in active transport.
question
A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of
answer
facilitated diffusion.
In facilitated diffusion, molecules use a transport protein to move across the plasma membrane. There is a net movement of molecules down the concentration gradient -- that is, there is a net movement of molecules from where they are more concentrated to where they are less concentrated.
question
Water crosses the plasma membrane
answer
through facilitated diffusion or diffusion.
question
The sodium-potassium pump uses energy from ATP to move sodium ions out of the cell, and potassium ions into the cell. This is an example of
answer
active transport.
The sodium-potassium pump moves ions across the plasma membrane against their concentration gradients. This requires energy and is an example of active transport.
question
The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of
answer
endocytosis
In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.
question
The movement of atoms, ions, or molecules from a region of higher concentration to regions of lower concentration is called _____.
answer
diffusion
Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of high concentration to an area of lower concentration.
question
What name is given to the process by which water crosses a selectively permeable membrane?
answer
Osmosis is the passive transport of water.
question
This cell is in a hypertonic solution.
answer
There is a greater concentration of solute outside the cell.
question
You know that this cell is in a(n) _____ solution because the cell _____.
answer
hypotonic ... swelled
Submit
A cell will gain water when placed in a hypotonic solution.
question
You know that this cell is in a(n) _____ solution because it _____.
answer
hypertonic solution ... lost water
A cell will lose water when placed in a hypertonic solution.
question
Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?
answer
the difference in water concentration across a selectively permeable membrane
The driving force for osmosis is water's concentration gradient across a selectively permeable membrane. Differences in solute concentration across a membrane create water concentration differences, but solute concentration differences do not directly drive osmosis.
question
Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.
answer
actively pump water back into their cells to counter its loss due to osmosis
A cell (in this case, cells within the body of a brine shrimp) will experience a net output of water in a hypertonic environment. For cells to prevent shriveling, they must actively recapture water from their surroundings.
question
In the process of osmosis, water displays a net movement from an area of __________ water concentration to an area of __________ water concentration.
answer
higher ... lower
Water displays a net movement down its concentration gradient. Movement down a concentration gradient is a characteristic of passive transport.
question
The concentration of solutes in a red blood cell is about 2%. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
answer
a hypertonic sucrose solution
Water moves by osmosis from the hypotonic environment, the cell interior, to the hypertonic environment.
question
Facilitated diffusion is a type of _____.
answer
passive transport
During facilitated diffusion, the cell is not expending energy to move the particles across the membrane; therefore, facilitated diffusion is a form of passive transport.
question
Review the figure below of passive transport, then choose one of the following statements as being descriptive of this process.
answer
Passive transport can transport molecules without the assistance of proteins from an area of high concentration to an area of lower concentration.
Submit
question
Which of these statements describes what occurs in facilitated diffusion?
answer
Facilitated diffusion of solutes occurs through protein pores in the membrane.
Protein pores are passageways for facilitated diffusion.
question
What condition might result from an excess of aquaporins?
answer
fluid retention in pregnant women
Aquaporins transport water. An excess of aquaporins during pregnancy can result in fluid retention.
question
When in solution, a molecule that moves slowly across an artificial membrane moves rapidly across a plasma membrane. This molecule rapidly enters the cell regardless of whether its concentration is higher inside or outside the cell. Using this information, which transport mechanism is most likely to be responsible for the movement of the molecule across a plasma membrane?
answer
active transport
Some transport proteins can move molecules against their concentration gradient in a process called active transport.
question
Endocytosis moves materials _____ a cell via _____.
answer
into ... membranous vesicles
The prefix "endo-" means "inward."
question
You can recognize the process of pinocytosis when _____.
answer
the cell is engulfing extracellular fluid
Pinocytosis is "cell drinking."
question
A white blood cell engulfing a bacterium is an example of _____.
answer
phagocytosis
Phagocytosis occurs when a cell engulfs a large particle.
question
Which statement best describes phagocytosis?
answer
A cell engulfs a particle by wrapping pseudopodia around it and packaging it within a vacuole.
After entry, the vacuole usually fuses with a lysosome, whose hydrolytic enzymes digest the contents of the vacuole.
question
A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via __________.
answer
endocytosis
Endocytosis is the procedure that cells use to import large molecules across their membranes. Review Figure 5.9 in the textbook.
question
Which of these is exhibiting kinetic energy?
answer
a space station orbiting Earth
Kinetic energy is energy of motion.
question
"Conservation of energy" refers to the fact that _____.
answer
energy cannot be created or destroyed but can be converted from one form to another
question
Chemical energy is a form of _____ energy.
answer
potential
Chemical energy is a form of stored energy.
question
In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?
answer
cellular respiration
This is the name given to the process by which the body converts food energy to energy stored in ATP.
question
Which of these are by-products of cellular respiration?
answer
heat and water
question
Light is _____ energy, which is converted by plants into molecules, which possess _____ energy.
answer
kinetic ... chemical
Light is kinetic energy, and molecules possess chemical energy. Chemical energy refers to the potential energy that can be released during chemical reactions.
question
Energy is conserved. This means that in any system, _____.
answer
total energy input equals total energy output
question
Kinetic energy is energy in motion. Potential energy is _____ energy.
answer
stored
question
Which of the following is highest in chemical energy?
answer
one molecule of glucose
question
In cellular respiration, most energy is released and transferred to ATP when _____.
answer
high-energy electrons "fall" to lower energy levels
question
The first law of thermodynamics _____.
answer
states that energy is neither created nor destroyed
The first law of thermodynamics states that energy can be transformed but can be neither created nor destroyed.
question
What happens to the chemical energy that is extracted from molecules by cellular activities but that is not used for cellular work?
answer
The energy contributes to the entropy of the system.
The second law of thermodynamics states that in any energy transformation, the overall disorder of the universe increases. Most often, this disorder comes in the form of thermal molecular motion (heat), which is a form of energy that is not lost but cannot be harnessed for work.
question
In plant cells, carbon dioxide and water are joined to form carbohydrates. Plant cells can also break down carbohydrates such as glucose, releasing carbon dioxide, water, and energy. No one has ever observed such reactions between water and carbon dioxide outside of living cells. What allows simple molecules to assemble into more complex molecules, and also disassemble, in cells but not in other, nonbiological environments?
answer
Cells couple energy-releasing reactions to energy-requiring reactions.
One of the many things cells do well is the linking of metabolic reactions in ways that allow an energy-yielding reaction to be coupled to an energy-requiring reaction. ATP molecules are the key to energy coupling.
question
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
answer
hydrolysis
Hydrolysis involves breaking bonds with the addition of water.
question
In this reaction _____.
answer
the products have less potential energy than the reactants
heat has been released to the environment
Submit
question
The reaction A --> B + C + heat is released in a(n) _____ reaction.
answer
exergonic
Energy has been released.
question
A(n) _____ reaction occurs spontaneously.
answer
exergonic
In exergonic reactions the products have less potential energy than the reactants.
question
Which of these reactions requires a net input of energy from its surroundings?
answer
endergonic
The products of endergonic reactions have more potential energy than the reactants.
question
In cells, what is usually the immediate source of energy for an endergonic reaction?
answer
ATP
The hydrolysis of ATP provides the energy needed for an endergonic reaction.
question
The reaction ADP + P --> ATP is a(n) _____ reaction.
answer
endergonic
Energy has been acquired from the surroundings.
question
The energy for an endergonic reaction comes from a(n) _____ reaction.
answer
exergonic
The energy released by an exergonic reaction can be used to drive an endergonic reaction.
question
What is the fate of the phosphate group that is removed when ATP is converted to ADP?
answer
It is acquired by a reactant in an endergonic reaction.
By acquiring the phosphate group the reactant acquires energy.
question
This graph illustrates a(n) _____ reaction.
answer
endergonic The products contain more potential energy than the reactants.
question
What is energy coupling?
answer
the use of energy released from an exergonic reaction to drive an endergonic reaction
question
The hydrolysis of DNA into nucleotides constitutes an exergonic reaction. Yet, DNA is quite stable. Why is this the case?
answer
The activation energy required to initiate this reaction is seldom reached.
An input of energy, termed the activation energy, is required to initiate this reaction.
question
Lactase is essential for digesting lactose in milk. This enzyme is specific for this sugar. Why?
answer
There is a precise compatibility between the active site and the lactose molecule.
The three-dimensional characteristics of the molecule provide for a precise interaction with the active site.
question
For an enzyme to catalyze a reaction there must be a specific fit between the __________ and the enzyme's __________.
answer
substrate ... active site
The shapes of these two components are complementary.
question
Antibiotics - for example, penicillin - cannot be used to treat viral infections, such as the common cold. Why?
answer
Antibiotics inhibit enzymes that are essential to the survival of bacteria only, not enzymes important to humans.
Antibiotics are designed specifically to fight bacterial infections. Many antibiotics, such as penicillin, inhibit a bacterial enzyme that is used to make protective cell walls. Neither animals nor viruses make such an enzyme and therefore are mostly unaffected by antibiotics.
question
Azidothymidine (AZT) is an antiretroviral drug used in the treatment of HIV. It shares a structural similarity to a nucleotide. What might be the mode of action for this drug?
answer
competitive inhibition
AZT and the nucleotide compete for the active binding site. When AZT binds to an enzyme known as reverse transcriptase, it blocks the replication of the genetic material of HIV.
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