Bio Exam 2 chapter 4 enzymes and cell transport

Question 1

The fluid mosaic model describes the plasma membrane as consisting of:
A) a phospholipid bilayer with embedded carbohydrates.
B) two layers of phospholipids with cholesterol sandwiched between them.
C) carbohydrates and phospholipids that can drift in the membrane.
D) diverse proteins embedded in a phospholipid bilayer.

Answer 1

D. The fluid mosaic model describes the plasma membrane as a phospholipid bilayer with diverse proteins embedded in it.

Question 2

Small, nonpolar, hydrophobic molecules such as fatty acids:
A) easily pass through a membrane’s lipid bilayer.
B) very slowly diffuse through a membrane’s lipid bilayer.
C) require transport proteins to pass through a membrane’s lipid bilayer. D) are actively transported across cell membranes.

Answer 2

A. Small, nonpolar, hydrophobic molecules such as fatty acids easily pass through a membrane’s lipid bilayer.

Question 3

Which of the following substances would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer?
A) O2
B) CO2
C) Na+
D) a small, nonpolar molecule such as butane (C4H10)

Answer 3

C. Na+ would have the most trouble crossing a biological membrane by diffusing through the lipid bilayer because it is a charged ion. Note: The exact choices of these questions in the exam WILL change. You need to recognize which molecules can cross the cell membrane and which cannot. Substances that CAN diffuse across the cell membrane: Small polar or nonpolar molecules (e.g., O2, CO2, H2O, NO, CH3CH2OH (ethanol), etc.) and nonpolar molecules (may be large, e.g., cholesterol, steroid hormones, fats, lipids). Substances that CANNOT diffuse across the cell membrane: Charged molecules (e.g., Na+, H+, K+, Ca2+, Cl-, etc.) and large polar molecules (e.g., sugar, complex carbohydrates, etc.).

Question 4

Oxygen crosses a plasma membrane by:
A) osmosis.
B) active transport.
C) pinocytosis.
D) passive transport.

Answer 4

D. Oxygen crosses a plasma membrane by passive transport. Note: Oxygen does not need a transporter to cross the membrane.

Question 5

Which of the following statements regarding diffusion is false?
A) Diffusion is a result of the thermal energy of atoms and molecules.
B) Diffusion requires no input of energy into the system.
C) Diffusion occurs when particles spread from areas where they are less concentrated to areas where they are more concentrated.
D) Diffusion occurs even after equilibrium is reached and no net change is apparent.

Answer 5

C. Diffusion occurs when particles spread from areas where they are more concentrated to areas where they are less concentrated, not the other way around.

Question 6

Diffusion does not require the cell to expend ATP. Therefore, diffusion is considered a type of:
A) exocytosis.
B) passive transport.
C) active transport.
D) endocytosis.

Answer 6

B. Diffusion is considered a type of passive transport because it does not require the cell to expend ATP.

Question 7

Osmosis can be defined as:
A) the diffusion of water through a semipermeable membrane.
B) the diffusion of nonpolar molecules.
C) active transport.
D) the diffusion of a solute.

Answer 7

A. Osmosis is the diffusion of water through a semipermeable membrane. Note: Osmosis does not mean simple absorption or passive absorption.

Question 8

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:
A) exhibit a net movement to the side with lower free water concentration.
B) exhibit a net movement to the side with higher free water concentration.
C) exhibit a net movement to the side with lower solute concentration. D) exhibit an equal movement in both directions across the membrane.

Answer 8

A. Water will exhibit a net movement to the side with lower free water concentration.

Question 9

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?
A) Water will leave the balloon.
B) Water will enter the balloon.
C) Sucrose will leave the balloon.
D) Sucrose will enter the balloon.

Answer 9

A. Water will leave the balloon. Note: Only water can cross the membrane, sucrose cannot. So water will move from the side with more water (less sucrose) to the side with less water (more sucrose). The % you see in the exam WILL change!

Question 10

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:
A) is isotonic to the protozoan.
B) is hypotonic to the protozoan.
C) contains a higher concentration of solutes than the protozoan.
D) is hypertonic to the protozoan.

Answer 10

B. The environment is hypotonic to the protozoan. Note: Fresh water is ALWAYS hypotonic to any content of any living organisms. The most hypotonic substance you can find is pure distilled water.

Question 11

A cell that neither gains nor loses water when it is immersed in a solution must be:
A) isotonic to its environment.
B) hypertonic to its environment.
C) hypotonic to its environment.
D) metabolically inactive.

Answer 11

A. The cell must be isotonic to its environment. Note: Most animal cells MUST be immersed in an isotonic environment to stay healthy. Animal cells immersed in a hypotonic environment will burst. A hypertonic environment will cause water to exit from the cell, and the cell will become shriveled, which can kill the cell. You are also expected to know human physiological saline is about 0.85% NaCl and determine what is hypertonic and what is hypotonic compared to the cell content.

Question 12

In a hypotonic solution, an animal cell will:
A) lyse.
B) experience turgor.
C) neither gain nor lose water.
D) shrivel.

Answer 12

A. The animal cell will lyse. Note: Water will keep rushing inside the cell, and the cell will burst (or undergo lysis).

Question 13

If placed in tap water, an animal cell will undergo lysis, whereas a plant cell will not. What accounts for this difference?
A) the expulsion of water by the plant cell’s central vacuole.
B) the relative impermeability of the plant cell wall to water.
C) the fact that plant cells are isotonic to tap water.
D) the relative inelasticity and strength of the plant cell wall.

Answer 13

D. The relative inelasticity and strength of the plant cell wall account for this difference. Note: Plant, fungal, and bacterial cells that have a thick rigid cell wall will stay “turgid” in a hypotonic environment.

Question 14

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.
A) isotonic.
B) hypotonic.
C) hypertonic.
D) hydrophilic.

Answer 14

B. The solution in the balloon is hypotonic relative to the solution in the beaker. Note: The numbers and answers in the actual exam will change. You should be able to figure out the meaning of hypotonic, hypertonic, and isotonic by now and determine that from the numbers.

Question 15

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?
A) Mix the blood in a salty solution to cause the RBCs to lyse.
B) Mix the blood in an isotonic solution and allow the WBCs to float to the top.
C) Mix the blood in a hypotonic solution, which will cause the RBCs to lyse.
D) Mix the blood in a hypertonic solution, which will cause the RBCs to lyse.

Answer 15

C. Mix the blood in a hypotonic solution, which will cause the RBCs to lyse. Note: RBCs also have aquaporin that enables them to absorb water much faster than WBCs. RBCs typically will lyse within 10 seconds of exposure to distilled water, but WBCs will take more than a minute. You can easily isolate WBCs that way by lysing all the RBCs by exposing them to distilled water.

Question 16

A plant cell in a hypotonic solution: A) becomes turgid because of an inflow of water.
B) bursts because of an inflow of water.
C) shrivels because of an outflow of water.
D) wilts because of an outflow of water.

Answer 16

A. The plant cell becomes turgid because of an inflow of water.

Question 17

You are adrift in the Atlantic Ocean, and, being thirsty, drink the surrounding seawater. As a result:
A) you quench your thirst.
B) your cells become turgid.
C) you dehydrate yourself.
D) your cells lyse from excessive water intake.

Answer 17

C. You dehydrate yourself. Note: Ocean water is about 3% NaCl, and your physiological saline is about 0.85% NaCl. You’ll definitely dehydrate (and die faster) if you drink seawater.

Question 18

Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient. A) energy and transport proteins . . . down.
B) transport proteins . . . down.
C) energy and transport proteins . . . against.
D) transport proteins . . . against.

Answer 18

B. Facilitated diffusion requires transport proteins and moves a substance down its concentration gradient.

Question 19

The molecules responsible for membrane transport are:
A) steroids.
B) phospholipids.
C) carbohydrates.
D) proteins.

Answer 19

D. Proteins are responsible for membrane transport.

Question 20

Which of the following statements is true among all types of passive transport?
A) Proteins are needed to transport molecules across the membrane.
B) The concentration gradient is the driving force.
C) Only small polar molecules are able to cross the plasma membrane. D) Ions never cross the plasma membrane by passive transport.

Answer 20

B. The concentration gradient is the driving force in all types of passive transport.

Question 21

Aquaporins:
A) allow water to cross the plasma membrane via facilitated diffusion.
B) allow water to cross the plasma membrane against its concentration gradient.
C) allow for the active transport of water.
D) are found in all cells.

Answer 21

A. Aquaporins allow water to cross the plasma membrane via facilitated diffusion.
Note: Aquaporins are found in RBCs and kidney cells to facilitate faster water movement.

Question 22

Which of the following processes can move a solute against its concentration gradient?
A) osmosis
B) passive transport
C) facilitated diffusion
D) active transport

Answer 22

D. Active transport can move a solute against its concentration gradient.

Question 23

Which of the following is a typical feature of an ATP-driven active transport mechanism?
A) The transport protein must cross to the correct side of the membrane before the solute can bind to it.
B) The transport protein is irreversibly phosphorylated as transport takes place.
C) The transport protein catalyzes the conversion of ADP to ATP.
D) The solute moves against the concentration gradient.

Answer 23

D. The solute moves against the concentration gradient.
Note: ATP transporters hydrolyze ATP to ADP to obtain energy to move substances against the concentration gradient.

Question 24

Which of the following statements regarding active transport is false?
A) Active transport uses ATP as an energy source.
B) Active transport can move a solute against its concentration gradient.
C) Active transport requires the cell to expend energy.
D) Active transport is driven by the concentration gradient.

Answer 24

D. Active transport is driven by the concentration gradient.
Note: Active transport is driven by an energy source. The energy source can come from hydrolysis of ATP or movement of electrons down an electrochemical gradient (such as in photosynthesis or cellular respiration).

Question 25

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? A) endocytosis B) exocytosis C) diffusion D) pinocytosis

Answer 25

B. Exocytosis could be responsible for its secretion.

Question 26

The process of a white blood cell engulfing a bacterium is: A) osmosis. B) receptor-mediated endocytosis. C) pinocytosis. D) phagocytosis.

Answer 26

D. Phagocytosis. Note: Phagocytosis is engulfing a solid; pinocytosis is engulfing liquids.

Question 27

Phagocytosis is to eating as pinocytosis is to: A) osmosis. B) drinking. C) chewing. D) lysis.

Answer 27

B. Drinking.

Question 28

Cells acquire LDLs by: A) diffusion. B) receptor-mediated endocytosis. C) pinocytosis. D) phagocytosis.

Answer 28

B. Receptor-mediated endocytosis. Note: LDL stands for low-density lipoprotein, and HDL stands for high-density lipoprotein. Both HDL and LDL are different forms of storage vesicles that the body uses for transporting cholesterol in the bloodstream. Cholesterol is actually EXTREMELY important for the body. Every single cell in your body needs cholesterol to synthesize cell membranes as well as making other sterol-based compounds. However, LDL vesicles tend to cling to the walls of blood vessels to trigger blockage (called plaques) and can increase your chance of a heart attack. On the other hand, HDL has the ability to lift small plaques from capillary walls and can reduce your chance of heart attack. Therefore, LDL is referred to as “bad cholesterol,” and HDL is called the “good cholesterol.” If someone asks you whether cholesterol is essential for the body, the answer is absolutely YES!

Question 29

In the reaction A → B + C + heat: A) there is a net input of energy. B) the potential energy of the products is greater than that of the reactant. C) the potential energy of the products is less than that of the reactant. D) entropy has decreased.

Answer 29

C. The potential energy of the products is less than that of the reactant.

Question 30

A steer must eat at least 100 pounds of grain to gain less than 10 pounds of muscle tissue. This illustrates: A) the first law of thermodynamics. B) the second law of thermodynamics. C) that some energy is destroyed in every energy conversion. D) that energy transformations are typically 100% efficient.

Answer 30

B. The second law of thermodynamics. Note: Organisms typically only convert less than 5% of the energy they consume as food into their own muscle mass. Therefore, consuming meat is a lot less energetically efficient than consuming plant-based food.

Question 31

Living systems: A) violate the first law of thermodynamics. B) violate the second law of thermodynamics. C) decrease their entropy while increasing the entropy of the universe. D) are examples of a closed system.

Answer 31

C. Decrease their entropy while increasing the entropy of the universe. Note: Living systems absolutely do NOT violate the second law of thermodynamics. Living organisms continuously burn energy to decrease entropy within. However, burning energy invariably increases the entropy of the universe.

Question 32

Which of the following processes is endergonic? A) the burning of wood B) the synthesis of glucose from carbon dioxide and water C) the breakdown of glucose D) cellular respiration

Answer 32

B. The synthesis of glucose from carbon dioxide and water. Note: That clearly requires input of energy and is therefore endergonic.

Question 33

What is the basic difference between exergonic and endergonic reactions? A) Exergonic reactions involve ionic bonds; endergonic reactions involve covalent bonds. B) Exergonic reactions involve the breaking of bonds; endergonic reactions involve the formation of bonds. C) Exergonic reactions release energy; endergonic reactions absorb it. D) In exergonic reactions, the reactants have less chemical energy than the products; in endergonic reactions, the opposite is true.

Answer 33

C. Exergonic reactions release energy; endergonic reactions absorb it.

Question 34

Which of the following examples is classified as a metabolic pathway? A) protein synthesis B) osmosis C) cell lysis D) passive diffusion

Answer 34

A. Protein synthesis. Note: Protein synthesis requires multiple steps and many enzymes to complete. It is definitely considered a “pathway.”

Question 35

When a cell uses chemical energy to perform work, it uses the energy released from a(n) ________ reaction to drive a(n) ________ reaction. A) exergonic . . . endergonic B) endergonic . . . exergonic C) exergonic . . . spontaneous D) spontaneous . . . exergonic

Answer 35

A. Exergonic . . . endergonic.

Question 36

Which of the following statements about the ATP molecule is true? A) It contains five phosphate groups. B) Extremely stable bonds link the second and third phosphate groups. C) It contains the sugar glucose. D) It releases energy when one phosphate group leaves ATP.

Answer 36

D. It releases energy when one phosphate group leaves ATP.

Question 37

Anything that prevents ATP formation will most likely: A) result in cell death. B) force the cell to rely on lipids for energy. C) force the cell to rely on ADP for energy. D) have no effect on the cell.

Answer 37

A. Result in cell death. Note: Cyanide poison inhibits ATP synthesis, and you’ll die quite quickly after exposure.

Question 38

ATP can be used as the cell's energy exchange mechanism because: A) endergonic reactions can be fueled by coupling them with the formation of ATP from ADP. B) ATP is the most energy-rich small molecule in the cell. C) endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP. D) ATP is a disposable form of chemical energy, used once and then discarded by the cell.

Answer 38

C. Endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP.

Question 39

The energy required to initiate an exergonic reaction is called: A) exergonic energy. B) endergonic energy. C) input energy. D) the activation energy.

Answer 39

D. The activation energy.

Question 40

Most of a cell's enzymes are: A) lipids. B) proteins. C) amino acids. D) carbohydrates.

Answer 40

B. Proteins.

Question 41

When an enzyme catalyzes a reaction: A) it lowers the activation energy of the reaction. B) it raises the activation energy of the reaction. C) it acts as a reactant. D) it is used once and discarded.

Answer 41

A. It lowers the activation energy of the reaction.

Question 42

Substrates bind to an enzyme's ________ site. A) allosteric B) inhibitory C) phosphate D) active

Answer 42

D. Substrates bind to an enzyme's active site. Note: Non-competitive inhibitors or other allosteric regulators bind to the allosteric site of an enzyme.

Question 43

The active site of an enzyme is: A) the region of a substrate that is changed by an enzyme. B) the highly changeable portion of an enzyme that adapts to fit the substrates of various reactions. C) the region of an enzyme that attaches to a substrate. D) the region of a product that detaches from the enzyme.

Answer 43

C. The active site of an enzyme is the region of an enzyme that attaches to a substrate.

Question 44

Which of the following statements regarding enzyme function is false? A) An enzyme's function depends on its three-dimensional shape. B) Enzymes are very specific for certain substrates. C) Enzymes are used up when they catalyze a chemical reaction, so must be synthesized for each new chemical reaction. D) Enzymes emerge unchanged from the reactions they catalyze.

Answer 44

C. Enzymes are used up when they catalyze a chemical reaction, so must be synthesized for each new chemical reaction. Note: Enzymes may change shape slightly when catalyzing a reaction, but they are not used up during the reaction. A very small amount of enzyme is needed to catalyze a lot of reactions.

Question 45

Which of the following statements regarding enzymes is true? A) Enzymes are inorganic. B) An enzyme's function is unaffected by changes in pH. C) Enzymes catalyze specific reactions. D) All enzymes depend on protein cofactors to function.

Answer 45

C. Enzymes catalyze specific reactions. Note: Most enzymes are made of protein, therefore organic. Enzyme functions are affected by temperature, pH, and salt concentrations. Only some enzymes depend on cofactors and coenzymes that are typically not protein.

Question 46

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.

Answer 46

D. Heating inactivates enzymes by changing the enzyme's three-dimensional shape.

Question 47

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

Answer 47

C. A zinc ion could be a cofactor. Note: Common cofactors include metallic ions such as Zn2+, Cu2+, Mo+, Mg2+, Mn+, Fe2+, or Fe3+. The choices in the exam may change!

Question 48

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

Answer 48

B. Vitamin B6 is a coenzyme. Note: Vitamin B complexes, vitamin C, and vitamin D are all common coenzymes. Coenzymes are typically carbon-containing organic compounds. Zinc, iron, and iodine are considered “cofactors.”

Question 49

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.

Answer 49

D. Competitive inhibitors bind to the active site of the enzyme; noncompetitive inhibitors bind to a different site. Note: Noncompetitive inhibitors typically bind to the allosteric site.

Question 50

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.

Answer 50

C. This is an example of feedback inhibition.

Question 51

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

Answer 51

A. Cell A depicts an animal cell placed in a solution hypotonic to the cell.

Question 52

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

Answer 52

D. Part D breaks free of the rest when an ATP molecule is used for energy.

Question 53

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's 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. Under normal conditions, the purified water would cross the membrane to dilute the more concentrated tap water solution. 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. D) move by passive transport to Tank B.

Answer 53

C. After the reverse osmosis system has been operating for 30 minutes, the solution in Tank A would be hypertonic to Tank B. Note: Tank A contains more solute, so it is hypertonic to Tank B. Reverse osmosis is a very common way to purify water or used for desalination. You apply energy to push water containing impurities or salt through a membrane to the other side. Only water can go through, and the impurities/salt will be left in the original solution. Cruise ships supply freshwater to passengers via reverse osmosis.

Question 54

If you shut the system off and pressure was no longer applied to Tank A, you would expect: A) the water to flow from Tank A to Tank B. B) the water to reverse flow from Tank B to Tank A. C) the water to flow in equal amounts in both directions. D) the water to flow against the concentration gradient.

Answer 54

B. The water would reverse flow from Tank B to Tank A.