Question 1

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?
A) Figure B shows the method used to obtain the data in Figure A.
B) Figure C is essentially a summary of the data in Figure A.
C) Figure A is about water movement, and Figures B and C are about presence of aquaporins.
D) Figure A has data for more than 2 hours, and Figures B and C show data all collected at the same time.

Accepted Answer

Figure A shows changes in permeability of tubules in response to vasopressin, while Figure C shows permeability of tissues to water before, during, and after vasopressin administration. Figure B shows the density of aquaporins in kidney tubule cells before, during, and after vasopressin administration. Therefore, Figure C is essentially a summary of the data in Figure A, as it shows the overall permeability changes in response to vasopressin.

Question 2

Heating inactivates enzymes by
A) breaking the covalent bonds that hold the molecule together.
B) removing phosphate groups from the enzyme.
C) causing enzyme molecules to stick together.
D) changing the enzyme's three-dimensional shape.

Accepted Answer

Heating can cause changes in temperature and/or pH, which can alter the conformation of the protein structure of the enzyme, leading to a loss of function. This is because the specific three-dimensional shape of an enzyme is crucial for its catalytic activity.

Question 3

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.
A) The number of aquaporins in the membrane is constant, but the pores have to be activated.
B) Aquaporins are inserted into the membrane as needed.
C) Aquaporins are only in cells that need to be permeable to water.
D) Aquaporins use ATP to pump water across the membrane, and their action is limited by the metabolic pathways that produce ATP.

Accepted Answer

The graph in Figure B shows that the density of aquaporins in kidney tubule cells increases rapidly after administration of vasopressin, indicating that the aquaporins are inserted into the membrane as needed. This suggests that aquaporins are not always present in the membrane, but are added quickly when necessary. This is consistent with what is known about aquaporins, which are regulated by various factors and can be rapidly inserted into or removed from the membrane in response to changes in the cell's environment.

Question 4

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
A) be hypotonic to tank B.
B) be isotonic to tank B.
C) be hypertonic to tank B.

Accepted Answer

Reverse osmosis removes minerals and impurities, making the water in tank B more pure than the water in tank A. This means that tank A is hypertonic (has a higher concentration of dissolved minerals) compared to tank B, which is why water molecules move from tank A to tank B during the reverse osmosis process.

Question 5

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?
A) The urine will be salty.
B) The urine will be dilute.
C) The urine will be concentrated.
D) There will be large volumes of urine.

Accepted Answer

The answer of Water movement is important in urine formation...

Question 6

Which part of the ATP molecule breaks free of the rest when an ATP molecule releases energy? 
A) part A
B) part B
C) part C
D) part D

Accepted Answer

The answer of Which part of the ATP molecule breaks...

Question 7

Which of the following is a coenzyme? A) zinc B) vitamin B₆ C) iron D) iodine

Accepted Answer

Coenzymes are organic molecules that work with enzymes to facilitate the enzymes' activity. Vitamin B6 is an essential coenzyme for many enzymatic reactions in the body. Zinc, iron, and iodine are important minerals for various cellular processes but are not considered coenzymes.

Question 8

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?
A) Lipase raises the activation energy required to hydrolyze proteins.
B) Lipase lowers the activation energy required to hydrolyze proteins.
C) Lipase raises the activation energy required to hydrolyze fats.
D) Lipase lowers the activation energy required to hydrolyze fats.

Accepted Answer

Lipase is an enzyme that helps break down fats into smaller molecules. Therefore, it lowers the activation energy required to hydrolyze fats.

Question 9

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?
A) Elevated body temperature will increase reaction rates in the child's cells and overload the limited number of enzymes found in the cell.
B) Elevated body temperatures may denature enzymes. This would interfere with the cell's abilities to catalyze various reactions.
C) Elevated body temperatures will increase the energy of activation needed to start various chemical reactions in the body. This will interfere with the ability of enzymes to catalyze vital chemical reactions.
D) Elevated body temperatures cause molecules to vibrate more quickly and prevent enzymes from easily attaching to reactants. This would slow vital body reactions.

Accepted Answer

Elevated body temperatures may denature enzymes, which can interfere with the cell's ability to catalyze various reactions. Lowering the temperature through an ice bath can help preserve the function of these enzymes and prevent further damage to the body's cells.

Question 10

How does inhibition of an enzyme-catalyzed reaction by a competitive inhibitor differ from inhibition by a noncompetitive inhibitor?
A) Competitive inhibitors interfere with the enzyme; noncompetitive inhibitors interfere with the reactants.
B) Competitive inhibitors bind to the enzyme reversibly; noncompetitive inhibitors bind to it irreversibly.
C) Competitive inhibitors change the enzyme's tertiary structure; noncompetitive inhibitors cause polypeptide subunits to dissociate.
D) Competitive inhibitors bind to the active site of the enzyme; noncompetitive inhibitors bind to a different site.

Accepted Answer

Inhibition of an enzyme-catalyzed reaction by a competitive inhibitor occurs when the inhibitor molecule binds to the active site of the enzyme, preventing the substrate from binding. Noncompetitive inhibitors, on the other hand, bind to the allosteric site of the enzyme, causing a conformational change in the enzyme that prevents the substrate from binding. So the main difference lies in the binding site of the inhibitors.

Question 11

Which figure depicts an animal cell placed in a solution hypotonic to the cell? 
A) cell A
B) cell B
C) cell C
D) cell D

Accepted Answer

The answer of Which figure depicts an animal cell placed...

Question 12

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) a solution of very low pH.
B) a solution of sterilized tap water.
C) a weak (low concentration) solution of salt water.
D) distilled water.

Accepted Answer

A weak solution of salt water (also known as saline solution) is the best choice for cleaning a wound as it helps to remove debris and bacteria and also maintains the natural moisture balance of the wound. Solutions of very low pH or distilled water can be harmful to the tissues and may delay healing. Sterilized tap water may be an option in some cases, but saline solution is preferred.

Question 13

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?
A) There would be a net flow of water from tank A to tank B.
B) There would be a net flow of water from tank B to tank A.
C) Water would flow in equal amounts in both directions.

Accepted Answer

Reverse osmosis works by creating a concentration gradient between the two tanks, with the tank holding the lower salt concentration receiving the water that has been filtered through the membrane. If tank B has a higher salt concentration than tank A, then when the system is turned off, the concentration gradient would be reversed, resulting in a net flow of water from tank A to tank B in an attempt to equalize the salt concentration.

Question 14

Which of the following substances could be a cofactor?
A) a protein
B) a polypeptide
C) a zinc atom
D) a ribosome

Accepted Answer

A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's activity. Zinc is an example of a metallic ion cofactor. A protein (A) or polypeptide (B) cannot be a cofactor because they are not non-protein chemical compounds or metallic ions. A ribosome (D) is not a cofactor because it is a macromolecular complex that synthesizes proteins, and does not participate in enzymatic reactions as a cofactor.

Question 15

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?
A) She added water that was hypotonic to the culture of organisms, and they ruptured.
B) She added seawater to which she had added too much salt, and they ruptured.
C) She added water isotonic to the organisms, causing too much water to move in and out of the organisms, and they ruptured.
D) She added too little salt to the seawater she added, and the organisms all lost too much water and shriveled up.

Accepted Answer

When the lab assistant added clean water that was hypotonic (had lower concentration of solutes) to the culture of organisms, water moved inside the organisms causing them to swell and eventually rupture. This leads to the scattering of bits and pieces of the organisms throughout the water seen under the microscope.

Question 16

Inhibition of an enzyme is irreversible when
A) a competitive inhibitor is involved.
B) a noncompetitive inhibitor is involved.
C) there is an abundance of substrate.
D) covalent bonds form between inhibitor and enzyme.

Accepted Answer

Irreversible inhibition occurs when covalent bonds form between the inhibitor and the enzyme, permanently altering its active site and inhibiting its function even after the inhibitor is removed. Choices A and B represent reversible inhibition, where the inhibitor is not permanently bound to the enzyme and can be displaced by increasing substrate concentration or other means. Choice C refers to saturation kinetics and does not necessarily entail any inhibition.

Question 17

If you shut off the system and pressure was no longer applied to tank A, you would expect the
A) net flow of water to be from tank A to tank B.
B) water to reverse net flow from tank B to tank A.
C) water to flow in equal amounts in both directions.

Accepted Answer

When pressure is no longer applied to tank A, the net flow of water will reverse and flow from tank B back into tank A due to the difference in water levels and the force of gravity.

Question 18

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
A) competitive inhibition.
B) noncompetitive inhibition.
C) feedback inhibition.
D) irreversible inhibition.

Accepted Answer

This is an example of feedback inhibition, where the end product of a metabolic pathway (in this case, tryptophan) acts as an inhibitor of an earlier step in the pathway (enzyme synthesis).

Question 19

What is true about the data in the accompanying figure? 
A) The solid line represents a reaction that has been catalyzed by an enzyme.
B) The dashed line represents a reaction that includes an enzyme and a cofactor.
C) Both lines represent endergonic reactions.
D) The energy of the products is higher than the energy of the reactants.

Accepted Answer

The answer of What is true about the data in...

Question 20

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?
A) People with heart failure often swell due to too much water from excess numbers of aquaporins.
B) Water retention (too much water) in pregnancy can be due to a decreased number of aquaporins.
C) Kidney failure and decreased urine production are due to increased numbers of aquaporins.
D) Small amounts of urine are produced by people who inherit a defect in the ability to make aquaporins.

Accepted Answer

The answer of Water that is filtered out of the...

Quiz 5: The Working Cell

Heating inactivates enzymes by

Which part of the ATP molecule breaks free of the rest when an ATP molecule releases energy?

Which of the following is a coenzyme?

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?

How does inhibition of an enzyme-catalyzed reaction by a competitive inhibitor differ from inhibition by a noncompetitive inhibitor?

Which figure depicts an animal cell placed in a solution hypotonic to the cell?

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

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?

Which of the following substances could be a cofactor?

Inhibition of an enzyme is irreversible when

If you shut off the system and pressure was no longer applied to tank A, you would expect the

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

What is true about the data in the accompanying figure?

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?