MB CH5: Homework
In cells, what is usually the immediate source of energy for an endergonic reaction?
ATP The hydrolysis of ATP provides the energy needed for an endergonic reaction.
Which of the following statements regarding enzymes is true?
Enzymes catalyze specific reactions.
What is the fate of the phosphate group that is removed when ATP is converted to ADP?
It is acquired by a reactant in an endergonic reaction. By acquiring the phosphate group the reactant acquires energy.
Which of the following is a typical feature of an ATP-driven active transport mechanism?
The solute moves against the concentration gradient.
Diffusion Drag the terms on the left to complete the sentences on the right.
When molecules move down their concentration gradient, they move from where they are *MORE CONCENTRATED* to where they are *LESS CONCENTRATED.* Diffusion across a biological membrane is called *PASSIVE TRANSPORT.*
Relaying a message from a membrane receptor to a molecule that performs a specific function within a cell occurs when
a signaling molecule binds to a protein that extends to the outside of the cell.
Which of the following substances could be a cofactor?
a zinc atom
Identify Structure A.
glycoprotein Structure A is composed of both a carbohydrate and a protein.
When an enzyme catalyzes a reaction,
it lowers the activation energy of the reaction.
Light is _____ energy, which is converted into _____ energy by plants.
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.
Which of the following is highest in chemical energy?
one molecule of glucose
Most enzymes are _____.
proteins
What is energy coupling?
the use of energy released from an exergonic reaction to drive an endergonic reaction
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
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.
Membrane phospholipids
are able to drift about in the plasma membrane.
Cells store energy that they use for work in the _____.
arrangement of atoms within molecules The bonds holding atoms together also contain potential energy, energy the cell harnesses when bonds are broken during metabolism.
A plant cell in a hypotonic solution
becomes turgid because of an inflow of water.
How do fatty acids travel through a cell membrane?
carrier proteins
Which figure depicts an animal cell placed in a solution hypotonic to the cell?
cell A
During enzymatic reactions, substrates are converted to products. A property of enzymes that facilitates this reaction is that they are catalysts and therefore _____.
change the rate of a reaction without being consumed by the reaction This permits enzyme molecules to be used repeatedly.
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?
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.
Living systems
decrease their entropy while increasing the entropy of the universe.
The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell. This describes the process of
endocytosis. In endocytosis, the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell.
"Conservation of energy" refers to the fact that _____.
energy cannot be created or destroyed but can be converted from one form to another This is what is meant by conservation of energy.
What is the correct label for "A"?
energy of activation The energy of activation must be overcome in order for a reaction to proceed.
Certain cells that line the stomach synthesize a digestive enzyme and secrete it into the stomach. This enzyme is a protein. Which of the following processes could be responsible for its secretion?
exocytosis
A molecule moves down its concentration gradient using a transport protein in the plasma membrane. This is an example of
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.
Bacterial production of the enzymes needed for the synthesis of the amino acid tryptophan declines with increasing levels of tryptophan and increases as tryptophan levels decline. This is an example of
feedback inhibition.
What condition might result from an excess of aquaporins?
fluid retention in pregnant women Aquaporins transport water. An excess of aquaporins during pregnancy can result in fluid retention.
Which of the following direct energy transfers is impossible in living systems?
heat to light energy
The cholesterol associated with animal cell membranes
helps to keep phospholipids from being too close to one another.
This cell is in a(n) _____ solution.
hypertonic There is a greater concentration of solute outside the cell.
You know that this cell is in a(n) _____ solution because the cell _____.
hypotonic ... swelled A cell will gain water when placed in a hypotonic solution.
New drugs are being developed to lower levels of circulating cholesterol. A successful drug would be one that _____.
increases the rate of LDL receptor-mediated endocytosis Because cholesterol levels in the blood reflect the balance of, addition to, and removal of cholesterol, anything that tips the balance in favor of removal will lower the concentration of circulating cholesterol. Increasing LDL receptor-mediated endocytosis will have exactly this effect.
Some protozoans have special organelles called contractile vacuoles that continually eliminate excess water from the cell. The presence of these organelles tells you that the environment
is hypotonic to the protozoan.
As a result of its involvement in a reaction, an enzyme _____.
is unchanged Enzymes are not changed as a result of their participation in a reaction.
The mechanism of enzyme action is to _____.
lower the energy of the activation of a reaction Enzymes lower the energy of the activation of a reaction.
In a hypotonic solution, an animal cell will
lyse.
In active transport,
molecules move across the plasma membrane against their concentration gradient. Molecules move against their concentration gradient in active transport.
What name is given to the process by which water crosses a selectively permeable membrane?
osmosis Osmosis is the passive transport of water.
The diffusion of water across a selectively permeable membrane is called __________.
osmosis This is a special case of passive transport for water.
Identify Structure D.
phospholipid bilayer of membrane Phospholipids can be recognized by the presence of a head and two tails.
Which of the following enables a cell to pick up and concentrate a specific kind of molecule?
receptor-mediated endocytosis In receptor-mediated endocytosis, only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, endocytosis does not proceed.
Cells acquire low-density lipoproteins (LDLs) by
receptor-mediated endocytosis.
Enzymes work by _____.
reducing activation energy
Anything that prevents ATP formation will most likely
result in cell death.
What is the function of Structure E?
stabilization of the phospholipids Cholesterol helps to stabilize the structure of the plasma membrane.
All cells are enclosed by a plasma membrane that is similar in ________ and ________.
structure; function
In this reaction _____.
the products have less potential energy than the reactants
The active site of an enzyme is
the region of an enzyme that attaches to a substrate.
Water crosses the plasma membrane
through facilitated diffusion or diffusion. Water can cross the plasma membrane through the process of facilitated diffusion. However, water molecules can also cross the lipid bilayer directly.
Energy is conserved. This means that in any system, _____.
total energy input equals total energy output
Structure A in the figure is a(n) _____.
transport protein The protein is allowing solute molecules to enter the cell.
Structure B is a _____.
transport protein The transport protein facilitates the movement of solute across the plasma membrane..
Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient.
transport proteins; down
Can you match these terms about enzymes to their descriptions? Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
1. An enzyme is considered a(n) *CATALYST* because it speeds up a chemical reaction without being used up. 2. In a catalyzed reaction, a reactant is often called a(n) *SUBSTRATE.* 3. An enzyme is specific because the shape of its *ACTIVE SITE* matches only particular reactants. 4. An enzyme speeds up reactions by lowering the *ACTIVATION ENERGY.* 5. The *INDUCED FIT* between an active site and its substrate often strains bonds and helps the reaction proceed. 6. A(n) *COENZYME,* which is often a vitamin, binds to an enzyme and plays a role in catalysis. 7. High temperatures or changes in pH can *DENATURE* an enzyme, causing it to lose its shape and biological activity.
Use the graph and your knowledge of enzymes to identify the three true statements about enzymes.
1. By binding to reactant molecules, enzymes make it easier for the bonds in the molecules to break apart. 2. Reactants cannot convert to products without an initial input of energy to start the reaction. 3. Enzymes lower the overall energy input needed for a reaction to occur. For a chemical reaction to begin, chemical bonds in the reactant molecules must be broken. This process requires that the molecules absorb energy from their surroundings. The energy that must be invested to start a reaction is called activation energy because it activates the reactants and triggers the chemical reaction. Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules.
Biologists use the fluid mosaic model to describe membrane structure. Which statements about the fluid mosaic structure of a membrane are correct? Select the three correct statements.
1. The framework of a membrane is a bilayer of phospholipids with their hydrophilic heads facing the aqueous environment inside and outside of the cell and their hydrophobic tails clustered in the center. 2. The diverse proteins found in and attached to membranes perform many important functions. 3. Because membranes are fluid, membrane proteins and phospholipids can drift about in the membrane. Membranes consist of diverse proteins suspended in and attached to a phospholipid bilayer. Kinks in the unsaturated fatty acid tails of some phospholipids keep the membrane fluid, and a mosaic of proteins perform a variety of functions.
Can you match these three tonicity terms with their descriptions? Drag the terms on the left to the appropriate blanks to complete the sentences. Terms can be used more than once.
1. The ideal osmotic environment for an animal cell is a(n) *ISOTONIC* environment. 2. An animal cell placed in a(n) *HYPOTONIC* solution will gain water, swell, and possibly burst. 3. There is a net diffusion of water out of an animal cell when it is placed in a(n) *HYPERTONIC* solution. 4. The ideal osmotic environment for a plant cell is a(n) *HYPOTONIC* environment. 5. A plant cell placed in a(n) *HYPERTONIC* solution will lose water and plasmolyze. 6. A plant cell surrounded by a(n) *ISOTONIC* solution will be flaccid (limp).
Which of these is hydrophobic like the interior of the plasma membrane?
A Lipid soluble molecules are hydrophobic.
Which statement best describes phagocytosis?
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.
Can you complete this concept map that reviews the basic concepts of energy? Drag the terms to the appropriate locations on the concept map.
A. Kinetic B. Potential C. Motion D. Chemical Energy E. Entropy F. Heat G. First law of Thermodynamics H. Second law of thermodynamics
Can you label some components associated with the plasma membrane and identify the functions of membrane proteins? Drag labels to targets in Group 1 to identify the main functions of membrane proteins. Drag labels to targets in Group 2 to identify some components associated with the plasma membrane.
A. Phospholipid bilayer B. Fibers of extracellular matrix (ECM) C. Enzymatic activity D. Microfilaments of cytoskeleton E. Attachment to ECM and cytoskeleton F. Signal reception and relay G. Transport H. Intercellular junctions I. Cell-cell recognition
Certain molecules use facilitated diffusion to cross the plasma membrane. Drag the labels to their appropriate locations on the diagram.
A. Plasma membrane B. Side with higher concentration of molecules C. Side with lower concentration of molecules D. Facilitated diffusion causes a net movement of molecules down their concentration gradient E. Transport protein
Certain molecules use diffusion to cross the plasma membrane. Drag the labels to their appropriate locations on the diagram.
A. Side with higher concentration of molecules B. Plasma membrane C. Side with lower concentration of molecules D. Diffusion causes a net movement of molecules down their concentration gradient
Certain molecules cross the plasma membrane through the process of active transport. Active transport requires an input of energy and moves molecules against their concentration gradient. Drag the labels to their appropriate locations on the diagram.
A. Side with lower concentration of square molecules B. Transport protein C. Energy input from the cell D. Plasma membrane E. Side with higher concentration of square molecules
Most cellular work is accomplished by _____ energizing molecules by _____ them.
ATP ... phosphorylating The energy released when ATP is broken down is used to energize molecules by phosphorylating them.
Which of the following statements regarding active transport is false?
Active transport is driven by the concentration gradient.
Which of the following is an accurate comparison of active transport and facilitated diffusion?
Active transport moves solutes against their concentration gradient; facilitated diffusion moves substances down their concentration gradient. Active transport involves moving solutes against their concentration gradient. Facilitated diffusion moves solutes down their concentration gradient. Active transport requires the use of ATP, whereas facilitated diffusion does not.
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?
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.
How does inhibition of an enzyme-catalyzed reaction by a competitive inhibitor differ from inhibition by a noncompetitive inhibitor?
Competitive inhibitors bind to the active site of the enzyme; noncompetitive inhibitors bind to a different site.
Frequently, transplanted organs are rejected by the recipient's body. How is this reaction related to plasma membranes?
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.
Why doesn't the antibiotic penicillin harm humans?
Human cells do not have cell walls. Penicillin inhibits an enzyme that bacteria use to make their cell walls; because humans do not have this enzyme, they are not harmed.
Which of the following statements about ATP is true?
It releases energy when one phosphate group leaves ATP.
Which of the following statements is true about passive transport?
Passive transport requires no expenditure of cellular energy. Passive transport is an example of diffusion down a concentration gradient, which is a spontaneous characteristic of matter.
Which of these statements is TRUE with regard to this animation?
Sodium and potassium ions are transported against their concentration gradients. Energy in the form of ATP is required for the sodium-potassium pump to pump both sodium and potassium ions against their concentration gradients. Three positively charged sodium ions are exchanged for two positively charged potassium ions. Thus, the cell experiences a net loss of positive ions.
Which of the following is an example of the second law of thermodynamics?
The aerobic respiration of glucose generates heat. The second law of thermodynamics states that every energy transformation makes the universe more disordered and that most energy transformations release heat.
Taq polymerase is an enzyme isolated from the organism Thermophilus aquaticus. This organism has been found living in the hot springs of Yellowstone National Park. This enzyme is used to copy human DNA from crime scenes. Most reactions are performed at ranges similar to those of the human body; however, what considerations should be made for optimum use of this enzyme?
The temperature should be raised. These enzymes are not denatured by high heat and work more efficiently at temperatures of around 70-75°C. If the temperature is not increased, then the reaction will occur at a much slower rate.
In the lab, you use a special balloon that is permeable to water but not sucrose to make an "artificial cell." The balloon is filled with a solution of 20% sucrose and 80% water and is immersed in a beaker containing a solution of 40% sucrose and 60% water. Which of the following will occur?
Water will leave the balloon.
In this diagram of the plasma membranes of two adjoining cells, identify the protein indicated by the white arrow, including its function.
a receptor protein that binds with a signaling molecule and relays the message into the cell by activating other molecules inside the cell Signaling proteins are part of signal transduction pathways that transmit external chemical signals into the cell.
Which of these is exhibiting kinetic energy?
a space station orbiting Earth Kinetic energy is energy of motion.
A man with a dirty cut on his hand appears at the emergency department for treatment. In order to clean the wound, the health-care provider should use
a weak (low concentration) solution of salt water.
Which of the following processes can move a solute against its concentration gradient?
active transport
Which of these are by-products of cellular respiration?
heat and water These are the by-products of cellular respiration.
You know that this cell is in a(n) _____ solution because it _____.
hypertonic solution ... lost water A cell will lose water when placed in a hypertonic solution.
Endocytosis moves materials _____ a cell via _____.
into ... membranous vesicles The prefix "endo-" means "inward."
An enzyme _____.
is an organic catalyst Enzymes are proteins that behave as catalysts.
Kinetic energy differs from chemical energy in that
kinetic energy is the energy of a moving object, whereas chemical energy is the potential energy of molecules.
Which part of the ATP molecule breaks free of the rest when an ATP molecule releases energy?
part D
Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of
passive transport.
When placed in a hypotonic environment, where the solute concentration is below that of the cell, a houseplant will _____.
remain standing upright The water balance in plants is remarkably different. In an isotonic solution plant cells will look flaccid (limp), and in a hypotonic environment they will be turgid (firm). The cell wall allows the plant cell to balance the osmotic pressures inside the cell.
Which characteristic promoted the utilization of lipids as the first cell membrane?
self-assembly into a simple membrane
Structure A is a _____.
solute A solute is crossing the plasma membrane.
Which of the following is a coenzyme?
vitamin B6
Aquaporins are proteins that facilitate the transport of __________ across the membrane.
water Aquaporins are a newly discovered class of transport proteins that transport water in cells with very high water permeability needs.
You are adrift in the Atlantic Ocean and, being thirsty, drink the surrounding seawater. As a result,
you dehydrate yourself.
Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer?
Na+
What is true about the data in the accompanying figure?
The dashed line represents a reaction that includes an enzyme and a cofactor.
Glucose molecules provide energy to power the swimming motion of sperm. In this example, the sperm are changing
chemical energy into kinetic energy.
The fluid mosaic model describes the plasma membrane as consisting of
diverse proteins embedded in a phospholipid bilayer.
This graph illustrates a(n) _____ reaction.
endergonic The products contain more potential energy than the reactants.
Which of these reactions requires a net input of energy from its surroundings?
endergonic The products of endergonic reactions have more potential energy than the reactants.
When a cell uses chemical energy to perform work, it uses the energy released from a(n) ________ reaction to drive a(n) ________ reaction.
exergonic; endergonic
Most of a cell's enzymes are
proteins.
In an oil-based, nonpolar environment, phospholipids would arrange themselves so that they __________.
would stay together but in a reverse orientation, with their tails projecting outward The fatty acid tails of a phospholipid remain nonpolar and the phosphate heads remain polar regardless of the surrounding environment. In an oily environment, the tables are turned relative to water; the polar heads will cluster together to avoid exposure to the oil, and the nonpolar tails will project outward into the nonpolar, oil-based surroundings.
Antibiotics - for example, penicillin - cannot be used to treat viral infections, such as the common cold. Why?
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.
Green olives may be preserved in brine, which is a 20-30% salt solution. How does this method prevent contamination by microorganisms?
Bacteria can't survive in a hypertonic solution because they lose water. If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.
Which statement regarding enzyme function is true?
Excessive salt ions can cause an enzyme to denature. Few enzymes can tolerate extremely salty conditions, because the salt ions interfere with some of the chemical bonds that maintain protein structure.
In a theoretical world where all things are possible, how could you increase the amount of energy that could be stored in a molecule of ATP?
Increase the negative charge of each phosphate group. Because the high energy of ATP hydrolysis depends on the strong charge repulsion between the negatively charged phosphates, anything that increases this repulsion would also increase the energy liberated when ATP is broken down to ADP + P.
Which of the following statements regarding membrane protein function is false?
Membrane proteins produce phospholipids.
Macrophages are white blood cells that roam the body searching for invading microbes. Inside macrophage vacuoles these invaders are destroyed. How do the microbes get inside the macrophages?
Microbes are engulfed into the macrophage via phagocytosis. Phagocytosis is a type of endocytosis in which a cell takes macromolecules, other cells, or particles packaged in vacuoles into its cytoplasm.
White blood cells (WBCs) are more resistant to lysis than red blood cells (RBCs). When looking at a sample of blood for WBCs, what could you do to reduce interference from RBCs?
Mix the blood in a hypotonic solution, which will cause the RBCs to lyse.
Review the figure below of passive transport, then choose one of the following statements as being descriptive of this process.
Passive transport can transport molecules without the assistance of proteins from an area of high concentration to an area of lower concentration. Passive transport involves the vibration of molecules, which causes them to randomly move from areas where they are more concentrated to areas where they are less concentrated. It requires no energy or proteins to cross the membrane.
A pharmaceutical company wishes to focus on an enzyme to develop new medications. What type of study would be of the greatest benefit?
Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity. Enzymes are the most common targets of drugs. By understanding the details of enzyme structure, new drugs can be designed and existing drugs can be better understood and potentially modified.
Inhibition of an enzyme is irreversible when
covalent bonds form between inhibitor and enzyme.
The reaction ADP + P --> ATP is a(n) _____ reaction.
endergonic Energy has been acquired from the surroundings.
Select the INCORRECT association.
exergonic ... uphill Exergonic reactions release energy.
In cellular respiration, most energy is released and transferred to ATP when _____.
high-energy electrons "fall" to lower energy levels
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
hydrolysis Hydrolysis involves breaking bonds with the addition of water.
A cell that has neither a net gain of water nor a net loss of water when it is immersed in a solution must be
isotonic to its environment.
You're on the pilot episode of a new game show called "The Transport Factor." The host hands you three different amino acids, four different sugars, and two different ions. Then the host shouts, "How many different proteins does the cell need to move these molecules across the plasma membrane using facilitated transport?" Quickly, you correctly respond: _____.
nine The specificity of transport proteins for the materials they transport is exactly like the specificity of enzymes for their substrates. Therefore, if there are nine different substances to be transported by facilitated diffusion, this almost certainly involves nine different transport proteins.
The plasma membrane is selectively permeable. Which of the following can pass freely through the membrane with no assistance?
oxygen and carbon dioxide Oxygen and carbon dioxide, as well as other small, hydrophobic molecules, can move freely across the membrane.
Facilitated diffusion is a type of _____.
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.
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?
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.
Most of the functions of a cell membrane, including transport and enzymatic function, are performed by
proteins.
The molecules responsible for membrane transport are
proteins.
The first law of thermodynamics _____.
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.
You can recognize the process of pinocytosis when _____.
the cell is engulfing extracellular fluid Pinocytosis is "cell drinking."
The transport of molecules of a particular solute from inside an animal cell across the cell membrane to the extracellular fluid always requires energy when _____.
the concentration of the solute is lower inside the cell than outside it To pump a molecule across a membrane against its concentration gradient, the cell must expend metabolic energy, which is provided by ATP. This type of membrane traffic is called active transport.
Osmosis can be defined as
the diffusion of water.
Plasma membranes are selectively permeable. This means that
the plasma membrane allows some substances to enter or leave a cell more easily than others.
In the reaction A → B + C + heat,
the potential energy of the products is less than that of the reactant.
In the figure below, working from the inside out, what would be the order of components observed?
water, hydrophilic head, hydrophobic tail, hydrophobic tail, hydrophilic head, water 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.
Can you match the processes involved in membrane transport to their descriptions? Drag the labels onto the chart to match each process with its description.
*Exocytosis* A vesicle inside the cell fuses with the plasma membrane and releases its contents outside the cell *Facilitated Diffusion* A form of passive transport. Molecules move across the plasma membrane using a transport protein *Endocytosis* The plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell *Diffusion* A form of passive transport. Molecules move across the plasma membrane by crossing the lipid bilayer *Active Transport* Requires energy from the cell. Molecules move against their concentration gradient
Which of the following is a difference between active transport and facilitated diffusion?
Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. Active transport can move substances against the concentration gradient, but it requires energy, usually in the form of ATP.
Which of the following statements regarding diffusion is false?
Diffusion occurs when particles spread from areas where they are less concentrated to areas where they are more concentrated.
A child is brought to the hospital with a fever of 107°F. Doctors immediately order an ice bath to lower the child's temperature. Which of the following statements offers the most logical explanation for this action?
Elevated body temperatures may denature enzymes. This would interfere with the cell's abilities to catalyze various reactions.
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 __________.
Endocytosis is the procedure that cells use to import large molecules across their membranes. Review Figure 5.9 in the textbook.
Which of these statements describes what occurs in facilitated diffusion?
Facilitated diffusion of solutes occurs through protein pores in the membrane. Protein pores are passageways for facilitated diffusion.
A group of single-cell organisms collected from the ocean was brought into the lab for examination. The lab assistant was concerned that the water had become full of toxic waste products and so added clean water to the culture. All of the organisms died, and when she looked at them under the microscope, all she could see were bits and pieces of them scattered throughout the water. What likely happened?
She added water that was hypotonic to the culture of organisms, and they ruptured.
Which of these statements about enzyme inhibitors is true?
The action of competitive inhibitors may be reversible or irreversible. Competitive inhibitors that bind covalently to the enzyme would be irreversible, and those that bind weakly would be reversible.
The hydrolysis of DNA into nucleotides constitutes an exergonic reaction. Yet, DNA is quite stable. Why is this the case?
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.
Which of the following statements regarding membrane function is false?
The plasma membrane is the control center of the cell.
Lactase is essential for digesting lactose in milk. This enzyme is specific for this sugar. Why?
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.
If you were working for a pharmaceutical company as part of a drug discovery team, which of these enzyme inhibitors would you suggest as a productive avenue for drug development?
a drug to treat high blood pressure that reversibly inhibits an enzyme catalyzing production of a chemical that causes blood vessels to contract
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?
a hypertonic sucrose solution Water moves by osmosis from the hypotonic environment, the cell interior, to the hypertonic environment.
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?
active transport Some transport proteins can move molecules against their concentration gradient in a process called active transport.
Aquaporins
allow water to cross the plasma membrane via facilitated diffusion.
Cellular respiration is an example of __________.
an exergonic process Cellular respiration is characterized by the breaking down of complex molecules and the release of energy.
In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP?
cellular respiration This is the name given to the process by which the body converts food energy to energy stored in ATP.
Heating inactivates enzymes by
changing the enzyme's three-dimensional shape.
The reaction A --> B + C + heat is released in a(n) _____ reaction.
exergonic Energy has been released.
A(n) _____ reaction occurs spontaneously.
exergonic In exergonic reactions the products have less potential energy than the reactants.
Which of the following statements regarding enzyme function is false?
Enzymes are used up when they catalyze a chemical reaction so must be synthesized for each new chemical reaction.
What is the basic difference between exergonic and endergonic reactions?
Exergonic reactions release energy; endergonic reactions absorb it.
After reading the paragraph below, answer the question that follows. Lipase is an enzyme released by the pancreas that digests fats in the small intestine; however, lipase is also found in bacteria. Researchers examined lipase function in two species of bacteria, species X and species Y. Data regarding the activity of lipase as a function of temperature are shown below for the lipase from bacteria X (white circles) and the lipase from bacteria Y (black circles). Use this information to answer the following three questions. Lipase activity as a function of temperature. What is true regarding the function of lipase?
Lipase lowers the activation energy required to hydrolyze fats.
Oxygen crosses a plasma membrane by
passive transport.
A steer must eat at least 100 pounds of grain to gain less than 10 pounds of muscle tissue. This illustrates
the second law of thermodynamics.
Which of the following statements regarding thermodynamics is false?
An automobile engine is a closed system because it does not exchange energy and matter with its surroundings.
After reading the paragraph below, answer the questions that follow. Water movement is important in urine formation in the kidneys. Urine is formed when the blood is filtered by the kidneys into kidney tubules. Three figures are presented here that relate to how the kidney tubules respond to the administration of the hormone vasopressin. The direction that water flows in these figures is from the kidney tubules back into the blood. Figure A. Changes in permeability of tubules in the kidney in response to the hormone vasopressin (AVP), which aids in osmoregulation. Figure B. Density of aquaporins in kidney tubule cells before, during, and after administration of vasopressin. Figure C. Permeability of tissues to water before, during, and after administration of vasopressin. Using the data from the graphs and what you know about membranes and metabolic pathways, predict which of the following is the likely reason why actions of aquaporins in a membrane can change so rapidly.
Aquaporins are inserted into the membrane as needed.
Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.
B ... the diffusion gradient there is steeper As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.
After reading the paragraph below, answer the questions that follow. Lipase is an enzyme released by the pancreas that digests fats in the small intestine; however, lipase is also found in bacteria. Researchers examined lipase function in two species of bacteria, species X and species Y. Data regarding the activity of lipase as a function of temperature are shown below for the lipase from bacteria X (white circles) and the lipase from bacteria Y (black circles). Use this information to answer the following three questions. Lipase activity as a function of temperature. What can you conclude from data in the figure?
Bacteria X likely lives in an environment that undergoes large changes in temperature.
After reading the paragraph below, answer the questions that follow. Water movement is important in urine formation in the kidneys. Urine is formed when the blood is filtered by the kidneys into kidney tubules. Three figures are presented here that relate to how the kidney tubules respond to the administration of the hormone vasopressin. The direction that water flows in these figures is from the kidney tubules back into the blood. Figure A. Changes in permeability of tubules in the kidney in response to the hormone vasopressin (AVP), which aids in osmoregulation. Figure B. Density of aquaporins in kidney tubule cells before, during, and after administration of vasopressin. Figure C. Permeability of tissues to water before, during, and after administration of vasopressin. How do the data in Figure A relate to the data in Figures B and C?
Figure C is essentially a summary of the data in Figure A.
Water that is filtered out of the blood by the kidneys is returned to the body through the action of aquaporins. Which of the following statements about water balance disorders is scientifically accurate?
People with heart failure often swell due to too much water from excess numbers of aquaporins.
Which of the following statements is true for all types of passive transport?
The concentration gradient is the driving force.
The eukaryotic cell has multiple membrane-enclosed compartments. This evolutionary innovation provides what advantage to the cell?
The different membrane-enclosed spaces allow different parts of the cell to perform specific functions. The membranes that surround organelles make it possible to construct very different chemical environments within and on the surface of each of these organelles.
What happens to the chemical energy that is extracted from molecules by cellular activities but that is not used for cellular work?
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.
Aspirin and other nonsteroidal anti-inflammatory drugs (NSAID) inhibit inflammation by inhibiting an enzyme in the prostaglandin pathway. However, inhibiting this enzyme also inhibits other pathways that protect the stomach from damage by stomach acid and that form blood clots. What can you conclude from this?
The enzyme is found in many different types of cells.
According to the second law of thermodynamics, which of the following is true?
The ordering of one system depends on the disordering of another. The second law of thermodynamics demands a total increase in entropy, but components of the system can increase in order at the expense of other components of the system.
Table sugar, or sucrose, is quite stable, and left on its own at room or even human body temperature, breakdown occurs very slowly. The breakdown of sucrose into the simple sugars fructose and glucose is an exergonic reaction. Sucrase, an enzyme, can increase the reaction rate at least one-million-fold. How does the net amount of energy released during the breakdown of sucrose compare between a spontaneous reaction and one catalyzed by sucrase?
The sucrase-catalyzed reaction releases the same amount of energy as the spontaneous reaction. The net yield of any quantity is the difference between what's gained and what's put in. In the case of the sucrase-catalyzed reaction and spontaneous (noncatalyzed) reactions, the trip up to and down from the activation energy barrier yields nothing, no matter how far the journey; all that matters is the difference in energy between product and reactant, something that remains constant, regardless of the rate of the reaction.
After reading the paragraph below, answer the questions that follow. Water movement is important in urine formation in the kidneys. Urine is formed when the blood is filtered by the kidneys into kidney tubules. Three figures are presented here that relate to how the kidney tubules respond to the administration of the hormone vasopressin. The direction that water flows in these figures is from the kidney tubules back into the blood. Figure A. Changes in permeability of tubules in the kidney in response to the hormone vasopressin (AVP), which aids in osmoregulation. Figure B. Density of aquaporins in kidney tubule cells before, during, and after administration of vasopressin. Figure C. Permeability of tissues to water before, during, and after administration of vasopressin. Based on the data from these figures, what do you expect the urine of a person to be like when vasopressin is having an effect on the kidney tubules?
The urine will be dilute.
After reading the paragraphs below, answer the questions that follow. Americans spend up to $100 billion annually for bottled water (41 billion gallons). The only beverages with higher sales are carbonated soft drinks. Recent news stories have highlighted the fact that most bottled water comes from municipal water supplies (the same source as your tap water), although it may undergo an extra purification step called reverse osmosis.Imagine two tanks that are separated by a membrane that is permeable to water, but not to the dissolved minerals present in the water. Tank A contains tap water and tank B contains the purified water. In the reverse osmosis process, pressure is applied to the tap water tank to force the water molecules across the membrane into the pure water tank. Suppose that while the reverse osmosis system is running tank B becomes contaminated with salt water such that it ends up with a higher salt concentration than tank A. What would happen if the reverse osmosis system was turned off?
There would be a net flow of water from tank A to tank B.
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 _____.
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.
After reading the paragraphs below, answer the questions that follow. Americans spend up to $100 billion annually for bottled water (41 billion gallons). The only beverages with higher sales are carbonated soft drinks. Recent news stories have highlighted the fact that most bottled water comes from municipal water supplies (the same source as your tap water), although it may undergo an extra purification step called reverse osmosis.Imagine two tanks that are separated by a membrane that is permeable to water, but not to the dissolved minerals present in the water. Tank A contains tap water and tank B contains the purified water. In the reverse osmosis process, pressure is applied to the tap water tank to force the water molecules across the membrane into the pure water tank. After the reverse osmosis system has been operating for 30 minutes, the solution in tank A would
be hypertonic to tank B.
Fluidity of an animal cell plasma membrane is enhanced by __________.
cholesterol molecules At low temperatures, cholesterol hinders solidification of the membrane because it prevents the close packing of phospholipids.
The movement of atoms, ions, or molecules from a region of higher concentration to regions of lower concentration is called _____.
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.
The phosphorylation of ADP to form ATP is an _____ reaction that _____ energy.
endergonic ... requires an input of Energy from exergonic reactions is used to store energy as a phosphate group is added to ADP.
ATP can be used as the cell's energy exchange mechanism because
endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP.
The energy for an endergonic reaction comes from a(n) _____ reaction.
exergonic The energy released by an exergonic reaction can be used to drive an endergonic reaction.
When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will
exhibit a net movement to the side with lower free water concentration.
Many physiological conditions are related to particular proteins in cell membranes. The number of insulin receptors in membranes is related to the amount of insulin present around those cells. If the presence of increased insulin results in a decrease in receptors and a decrease in insulin results in an increase in insulin receptors, this would be an example of
feedback inhibition.
When considering the formation of membranes, they __________.
form spontaneously in aqueous environments Membranes form spontaneously in aqueous environments such as those in which cells live. The phospholipids orient themselves so that the hydrophobic tails point inward and the hydrophilic heads point outward.
In this reaction _____.
heat has been released to the environment The potential energy of the products is less than that of the reactants.
In the process of osmosis, water displays a net movement from an area of __________ water concentration to an area of __________ water concentration.
higher ... lower Water displays a net movement down its concentration gradient. Movement down a concentration gradient is a characteristic of passive transport.
In the lab, you use a special balloon that is permeable to water but not sucrose to make an "artificial cell." The balloon is filled with a solution of 20% sucrose and 80% water and is immersed in a beaker containing a solution of 40% sucrose and 60% water. The solution in the balloon is ________ relative to the solution in the beaker.
hypotonic
The synthesis of an amino acid follows this pathway: precursor A > intermediate B > amino acid C. Each reaction is catalyzed by a different enzyme. This metabolic pathway is controlled by feedback inhibition with amino acid C inhibiting the conversion of precursor A to intermediate B. Amino acid C acts as a _____ of the first enzyme in the pathway.
noncompetitive inhibitor In this form of feedback inhibition, the end product of the pathway inhibits an early-acting enzyme. Because the product of the pathway and the substrate of the early-acting enzyme are very different in structure, competitive inhibition is unlikely as this involves binding of an inhibitor to the active site. Much more plausible is noncompetitive inhibition in which the inhibitor binds to a site on the enzyme that is different from the active site.
A white blood cell engulfing a bacterium is an example of _____.
phagocytosis Phagocytosis occurs when a cell engulfs a large particle.
The process of a white blood cell engulfing a bacterium is
phagocytosis.
The transfer of a phosphate group to a molecule or compound is called
phosphorylation.
Chemical energy is a form of _____ energy.
potential Chemical energy is a form of stored energy.
An energy barrier
prevents the spontaneous breakdown of molecules in the cell.
Which curve shows the course of the reaction in the presence of an enzyme--the black curve or the red curve? Which line represents the activation energy for that reaction--a, b, or c?
red curve; line b
The lipids in a cell membrane are arranged _____.
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.
Kinetic energy is energy in motion. Potential energy is _____ energy.
stored
What name is given to the reactants in an enzymatically catalyzed reaction?
substrate This is the name given to the reactants in an enzymatically catalyzed reaction.
For an enzyme to catalyze a reaction there must be a specific fit between the __________ and the enzyme's __________.
substrate ... active site The shapes of these two components are complementary.
Succinylcholine is structurally almost identical to acetylcholine, but if combined with the enzyme that normally hydrolyzes acetylcholine, the enzyme is no longer able to hydrolyze acetylcholine. This suggests that __________.
succinylcholine must be a competitive inhibitor of acetylcholine Competitive inhibition occurs when a molecule mimics the substrate and binds to the enzyme's active site.
Osmosis is often viewed incorrectly as a process driven directly by differences in solute concentration across a selectively permeable membrane. What really drives osmosis?
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.
What controls the net direction of molecules, such as oxygen, involved in passive transport?
the direction of the oxygen concentration gradient The direction a material moves in passive transport is determined by the material's concentration gradient, with material diffusing from regions of higher concentration to regions of lower concentration.
Which of the following statements is true of an exergonic reaction, but NOT true of an endergonic reaction?
the potential energy of the products is less than the potential energy of the reactants Since an endergonic reaction has a net energy release, the potential energy of the products must be less than the potential energy of the reactants.
If placed in tap water, an animal cell will undergo lysis, whereas a plant cell will not. What accounts for this difference?
the relative inelasticity and strength of the plant cell wall
You are working on a team that is designing a new drug. For this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells?
the similarity of the drug molecule to other molecules that are transported into the target cells If the target cells have transport proteins that specifically bind to certain molecules, they may bind with and transport a drug that is similar in structure.
Which of the following processes is classified as a metabolic pathway?
the synthesis of a protein
Which of the following processes is endergonic?
the synthesis of glucose from carbon dioxide and water
After reading the paragraphs below, answer the questions that follow. Americans spend up to $100 billion annually for bottled water (41 billion gallons). The only beverages with higher sales are carbonated soft drinks. Recent news stories have highlighted the fact that most bottled water comes from municipal water supplies (the same source as your tap water), although it may undergo an extra purification step called reverse osmosis.Imagine two tanks that are separated by a membrane that is permeable to water, but not to the dissolved minerals present in the water. Tank A contains tap water and tank B contains the purified water. In the reverse osmosis process, pressure is applied to the tap water tank to force the water molecules across the membrane into the pure water tank. If you shut off the system and pressure was no longer applied to tank A, you would expect the
water to reverse net flow from tank B to tank A.
