Ch.5 Evert The Flow of Energy Complete Test Bank

Chapter 5: The Flow of Energy

Multiple-Choice Questions

Of the total solar energy that reaches the Earth, ______ percent is captured by the cells of photosynthetic organisms.

a. about 50

b. about 20

c. about 10

d. about 5

e. less than 1

The energy of a system is defined as:

a. the amount of caloric present.

b. the amount of ATP present.

c. its capacity to do work.

d. the sum total of its chemical bonds.

e. the speed at which its atoms and molecules move.

According to the first law of thermodynamics, the total energy of ______ is ______.

a. a system; constant

b. a system; changeable

c. the surroundings; constant

d. the universe; constant

e. the universe; changeable

The first law of thermodynamics states that:

a. all natural processes proceed in such a direction that the disorder of the universe increases.

b. the activation energy of chemical reactions is raised by enzymes.

c. energy can be changed from one form to another, but it cannot be created or destroyed.

d. ΔG = ΔH - TΔS.

e. ATP is the energy currency of the cell.

Which of the following is NOT an example of potential energy?

a. A charged flashlight battery

b. A boulder at the top of a hill

c. A tank of gasoline

d. Water at the bottom of a waterfall

e. An apple on a branch

The first law of thermodynamics states that the total energy of a system and its surroundings after an energy conversion is ______ the total energy before the conversion.

a. equal to

b. greater than or equal to

c. greater than

d. less than

e. less than or equal to

One way of stating the second law of thermodynamics is:

a. although energy can be changed from one form to another, it can be neither created nor destroyed.

b. the entropy of the universe is increasing.

c. free energy is equal to the total potential energy minus the entropy.

d. enthalpy is the total potential energy of a system.

e. the activation energy of a reaction is always positive.

The second law of thermodynamics states that if no energy enters or leaves the system under study, the potential energy of the final state will be______ the potential energy of the initial state.

a. equal to

b. greater than or equal to

c. greater than

d. less than

e. less than or equal to

An exergonic reaction:

a. is a reaction in which the potential energy of the final state is less than that of the initial state.

b. does not take place spontaneously.

c. requires an input of energy from the outside.

d. has a positive free-energy change.

e. has a positive ΔG value.

ΔH refers to the:

a. heat released in an exergonic reaction.

b. heat released in an endergonic reaction.

c. change in enthalpy.

d. change in entropy.

e. exact change in potential energy.

Entropy refers to the ______ of a system.

a. heat content

b. free energy

c. potential energy

d. disorder or randomness

e. kinetic energy

ΔG refers to the change in ______ of the system.

a. the total heat content

b. free energy

c. entropy

d. enthalpy

e. the randomness

Which of the following equations relating enthalpy, entropy, and free energy is correct?

a. ΔS = ΔH - T ΔG

b. ΔH = ΔG - T ΔS

c. ΔS = ΔG + T ΔH

d. ΔG = ΔH - T ΔS

e. ΔG = ΔH + T ΔS

In all naturally occurring processes:

a. ΔH is positive.

b. ΔH is negative.

c. ΔS is positive.

d. ΔS is negative.

e. ΔG is negative.

The second law of thermodynamics states that all naturally occurring processes:

a. are exothermic.

b. are endothermic.

c. are exergonic.

d. are endergonic.

e. proceed with an increase in entropy.

Which of the following statements about living cells is FALSE?

a. They expend energy to maintain order.

b. They are at equilibrium with their surroundings.

c. They are open systems.

d. They transform energy.

e. As they transform energy, they dissipate heat.

Oxidation is defined as the:

a. loss of electrons.

b. loss of protons.

c. loss of electrons and protons.

d. gain of electrons.

e. gain of protons.

In biological reactions, when a molecule is oxidized it ______ an electron and a(n) ______.

a. loses; proton

b. gains; proton

c. loses; oxygen atom

d. gains; oxygen atom

e. loses; neutron

In the following reaction, which molecule is oxidized?

glucose + oxygen → carbon dioxide + water

a. Glucose

b. Oxygen

c. Carbon dioxide

d. Water

e. Carbon dioxide and water are reduced.

During the oxidation of glucose in the cell, most of the energy is released:

a. all at once.

b. in small amounts.

c. via mechanisms that require many kinds of molecules.

d. via mechanisms that result in high temperatures.

e. in a way that requires the input of 686 kilocalories of energy.

An enzyme:

a. is typically effective only in large amounts.

b. is a type of carbohydrate.

c. raises the activation energy of its reaction.

d. functions as a catalyst.

e. is permanently altered during the course of its reaction.

Most enzymes are:

a. RNA molecules.

b. proteins.

c. carbohydrates.

d. lipids.

e. DNA molecules.

A substrate binds to its enzyme at a location called the ______ site.

a. coenzyme

b. substrate

c. active

d. polypeptide

e. cofactor

A negatively charged portion of a substrate molecule would most likely fit into a ______ region of its enzyme’s active site.

a. positively charged

b. negatively charged

c. hydrophilic

d. hydrophobic

e. polar

The general name for a nonprotein component required by some enzymes is a:

a. metal ion.

b. cofactor.

c. substrate.

d. prosthetic group.

e. coenzyme.

Most enzymes that catalyze phosphorylation reactions require ______ as a cofactor.

a. NAD⁺

b. Mg²⁺

c. Ca²⁺

d. AMP

e. an iron-sulfur cluster

The vitamin niacin is part of the ______ molecule.

a. ferredoxin

b. iron-sulfur

c. pyridoxal phosphate

d. pyrophosphate

e. NAD⁺

In a NAD+ molecule, a pyrophosphate bridge joins:

a. two nicotinamide molecules.

b. two adenine molecules.

c. one ribose molecule with one nicotinamide molecule.

d. two ribose molecules.

e. one ribose molecule with one adenine molecule.

Which of the following statements about metabolic pathways is FALSE?

a. The enzymes of some pathways are segregated inside specific organelles.

b. The enzymes of some pathways are embedded in specific membranes.

c. The enzymes of most pathways allow intermediate products to accumulate.

d. Exergonic reactions in the pathway will pull forward preceding reactions.

e. The products from exergonic reactions will push along subsequent reactions.

Isozymes are:

a. RNA molecules that catalyze metabolic reactions.

b. identical coenzymes that require different metal ions.

c. identical coenzymes located in different parts of the cell.

d. different enzymes that catalyze identical reactions.

e. identical enzymes that catalyze different reactions.

As the temperature increases, the rate of an enzyme-catalyzed reaction usually:

a. increases constantly.

b. increases up to a point, then decreases.

c. decreases constantly.

d. decreases to a point, then increases.

e. increases, then decreases, then increases again.

Which of the following statements concerning the effect of pH on enzyme activity is FALSE?

a. Enzyme shape changes as the pH changes.

b. The pH affects positively-charged amino acids.

c. The pH affects negatively-charged amino acids.

d. The binding capacity of an enzyme is affected by pH.

e. Enzymes are always present at their pH optimum.

Denaturation of an enzyme refers to the:

a. proper arrangement of the enzyme in a metabolic pathway.

b. improper arrangement of the enzyme in a metabolic pathway.

c. loss of the enzyme’s proper shape.

d. formation of the enzyme’s proper shape.

e. formation of a new isozyme for that enzyme.

A regulatory enzyme in a metabolic pathway is most likely to be the:

a. last enzyme in the pathway.

b. first enzyme in the pathway.

c. enzyme that catalyzes the fastest reaction in the pathway.

d. enyzme that binds its coenzyme the fastest.

e. enzyme that lacks an effector site.

In an allosteric enzyme, the substrate binds at the ______ site and the regulatory substance binds at the ______ site.

a. active; effector

b. effector; active

c. active; inhibitor

d. inhibitor; active

e. inhibitor; effector

In feedback inhibition, the ______ enzyme in a metabolic pathway is inhibited by the ___________.

a. last; first substrate

b. last; end product

c. first; cofactor

d. first; first substrate

e. first; end product

Which of the following is NOT a component of an ATP molecule?

a. adenine

b. a pyrophosphate bridge

c. phosphate groups

d. a phosphoanhydride bond

e. ribose

In an ATP molecule, phosphoanhydride bonds link:

a. adenine to ribose.

b. adenine to a phosphate group.

c. the phosphate groups together.

d. ribose to a phosphate group.

e. the ribose groups together.

Which type of enzyme catalyzes the following reaction?

ATP + H₂O → ADP + phosphate

a. phosphorylase

b. ATPase

c. ADPase

d. kinase

e. phosphatase

Which statement about the reaction ATP + H₂O → ADP + phosphate is FALSE?

a. It is catalyzed by an ATPase.

b. It releases about 7.3 kilocalories of energy per mole.

c. It involves the breaking of phosphoanhydride bonds.

d. The reactants are more stable than the products.

e. It is exergonic.

Which of the following is a phosphorylation reaction catalyzed by a kinase in plant cells?

a. ATP + glucose → glucose phosphate + ADP

b. Fructose phosphate + ADP → fructose + ATP

c. Glucose phosphate + ADP → glucose + ATP

d. ATP + H₂O → ADP + phosphate

e. ADP + phosphate → ATP + H₂O

Which of the following statements about sucrose synthesis is FALSE?

a. Under standard thermodynamic conditions sucrose synthesis is endergonic.

b. In the cell, sucrose synthesis is endergonic.

c. In the cell, sucrose synthesis involves the phosphorylation of glucose.

d. In the cell, sucrose synthesis involves the phosphorylation of fructose.

e. In the cell, sucrose synthesis is coupled with ATP hydrolysis.

True-False Questions

The heat released in the exhaust of an engine can produce work.

When energy is changed from one form to another, the total energy after the change is equal to the total energy before the change.

An endergonic reaction is one that releases energy.

Picking up clothes from the floor and hanging them in a closet results in an increase in entropy.

The overall charge in energy that determines the course of a chemical reaction is the free-energy charge, ΔG.

The relationship between changes in free energy, enthalpy, and entropy that occur during a reaction can be expressed by the equation: ΔG = ΔH + T ΔS.

Oxidation and reduction always take place simultaneously.

When an atom is reduced, it loses electrons.

Enzymes function by raising the activation energy of specific reactions.

All enzymes are proteins.

An enzyme binds with its substrate at the active site.

A metal ion can be a cofactor.

A coenzyme is type of protein.

A nucleotide is composed of a nucleoside plus a phosphate group.

Plants, like humans, are unable to synthesize all of their required vitamins.

In a metabolic pathway, there is little accumulation of intermediate products.

A principal factor regulating enzyme activity in cells is the amount of substrate available.

When an enzyme is denatured it loses its shape.

For most enzyme catalyzed reactions, the rate approximately doubles for each 5C increase in temperature.

pH affects the rate of enzyme-catalyzed reactions by altering the charge on the enzyme and/or substrate(s).

In an allosteric enzyme, the substrate binds to the effector site.

An ATP molecule contains at least one pyrophosphate bridge.

An ATP molecule contains at least one phosphoester bond.

A coupled reaction is one in which an endergonic reaction is driven by an exergonic reaction.

Kinases are enzymes that catalyze phosphorylation reactions.

.

Essay Questions

1. The Laws of Thermodynamics; pp. 95–98; difficult

State the first and second laws of thermodynamics. How do they relate to living organisms?

2. The Laws of Thermodynamics; p. 97; moderate

State in words the meaning of the equation ΔG = ΔH - T ΔS.

3. The Laws of Thermodynamics; p. 97; difficult

Explain the meaning of the sentence, “Life can exist because the universe is running down.”

4. Oxidation-Reduction; p. 98; moderate

Explain the term “redox reactions.” Why do the two types of reactions included in this term always occur simultaneously?

5. Oxidation-Reduction; p. 99; easy

What is the advantage of releasing energy from their fuel molecules in small amounts?

6. Enzymes; p. 100; moderate

Define the term enzyme. What is the role of enzymes in cells?

7. Enzymes; p. 100 (Fig. 5-5); difficult

Define the term energy of activation. To illustrate this concept, draw a graph showing how the energy of activation is related to enzyme activity.

8. Enzymes; pp. 100–101; moderate

Describe the steps in an enzyme-catalyzed reaction.

9. Cofactors in Enzyme Action; pp. 101–102; moderate

Distinguish between the terms “cofactor,” “coenzyme,” and “prosthetic group.”

10. Metabolic Pathways; p. 102; easy

Discuss the advantages to the cell of arranging enzyme-catalyzed reactions into metabolic pathways.

11. Regulation of Enzyme Activity; p. 104; moderate

How do allosteric enzymes function? What role do they play in the cell?

12. Regulation of Enzyme Activity; p. 104; moderate

Describe the process of feedback inhibition. Why is this process important in the cell?

13. The Energy Factor: ATP; pp. 104-105; moderate

What is the typical role of ATP in coupled reactions in plant cells?

14. The Energy Factor: ATP; p. 105; moderate

Use the synthesis of sucrose from glucose and fructose to illustrate how an endergonic reaction can be coupled to an exergonic reaction.