AP Bio Ch 6 Practice Questions

Which is the most abundant form of energy in a cell? A. electrochemical gradients B. kinetic energy C. heat D. chemical energy E. mechanical energy

chemical energy

Which of the following statements about allosteric proteins is/are true? A. They are acted on by inhibitors. B. They are sensitive to environmental conditions. C. They exist in active and inactive conformations. D. All of the first three listed responses are correct. E. None of the three listed responses is correct.

All of the first three listed responses are correct.

Which of the following statements about enzymes is incorrect? A. Most enzymes are proteins. B. An enzyme lowers the activation energy of a chemical reaction. C. Enzymes can be used to accelerate both anabolic and catabolic reactions. D. An enzyme is consumed during the reaction it catalyzes. E. An enzyme is very specific in terms of which substrate it binds to.

An enzyme is consumed during the reaction it catalyzes.

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _______ is to _______. A. work; energy B. exergonic; endergonic C. free energy; entropy D. entropy; enthalpy E. exergonic; spontaneous

exergonic; endergonic

Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous? A. TΔS B. ΔS C. All of these values reveal the direction in which a reaction will go. D. ΔG E. ΔH

ΔG

Which of the following correctly states the relationship between anabolic and catabolic pathways? A. Degradation of organic molecules by anabolic pathways provides the energy to drive catabolic pathways. B. Energy derived from catabolic pathways is used to drive the breakdown of organic molecules in anabolic pathways. C. The flow of energy between catabolic and anabolic pathways is reversible. D. Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways. E. Catabolic pathways produce usable cellular energy by synthesizing more complex organic molecules.

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

Which of the following metabolic processes can occur without a net influx of energy from some other process? A. glucose + fructose → sucrose B. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O C. 6 CO2 + 6 H2O → C6H12O6 + 6 O2 D. amino acids → protein E. ADP + i → ATP + H20

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O

Which of the following states the relevance of the first law of thermodynamics to biology? A. The total energy taken in by an organism must be greater than the total energy stored or released by the organism. B. Energy can be freely transformed among different forms as long as the total energy is conserved. C. Photosynthetic organisms produce energy in sugars from sunlight. D. Living organisms must increase the entropy of their surroundings. E. Energy is destroyed as glucose is broken down during cellular respiration

Energy can be freely transformed among different forms as long as the total energy is conserved.

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously? A. Heat is being used by the organism as a source of energy. B. In this situation, the second law of thermodynamics must not apply. C. The entropy of the organism's environment must also be decreasing. D. Energy input into the organism must be occurring to drive the decrease in entropy. E. The first law of thermodynamics is being violated.

Energy input into the organism must be occurring to drive the decrease in entropy.

Which of the following statements about enzymes is true? A. Enzymes increase the rate of a reaction by raising the activation energy for reactions. B. The more heat that is added to a reaction, the faster the enzymes will function. C. Enzymes react with their substrate (form chemical bonds), forming an enzyme-substrate complex, which irreversibly alters the enzyme. D. Enzymes speed up the rate of the reaction without changing the DG for the reaction. E. All of the listed responses are correct

Enzymes speed up the rate of the reaction without changing the DG for the reaction.

Under most conditions, the supply of energy by catabolic pathways is regulated by the demand for energy by anabolic pathways. Considering the role of ATP formation and hydrolysis in energy coupling of anabolic and catabolic pathways, which of the following statements is most likely to be true? A. High levels of ATP act as an allosteric activator of catabolic pathways. B. High levels of ADP act as an allosteric inhibitor of anabolic pathways. C. High levels of ADP act as an allosteric inhibitor of catabolic pathways. D. High levels of ADP act as an allosteric activator of catabolic pathways E. High levels of ATP act as an allosteric activator of anabolic pathways.

High levels of ADP act as an allosteric activator of catabolic pathways

When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations? A. Cells are less efficient at energy metabolism than reactions that are optimized in a test tube. B. Cells have the ability to store heat; this cannot happen in a test tube. C. The amount of heat released by a reaction has nothing to do with the free energy change of the reaction. D. In cells, ATP is hydrolyzed to ADP and Pi, but in the test tube it is hydrolyzed to carbon dioxide and water. E. In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.

In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.

What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction? A. The more negative the ΔG, the faster the reaction is. B. The sign determines whether the reaction is spontaneous, and the magnitude determines the speed. C. Neither the sign nor the magnitude of ΔG have anything to do with the speed of a reaction. D. The sign does not matter, but the smaller the magnitude of ΔG, the faster the reaction. E. The sign does not matter, but the larger the magnitude of ΔG, the faster the reaction.

Neither the sign nor the magnitude of ΔG have anything to do with the speed of a reaction.

Which of the following environments or actions would not affect the rate of an enzyme reaction? A. pH B. heating the enzyme C. substrate concentration D. cooling the enzyme E. None of the listed responses is correct.

None of the listed responses is correct.

If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur? A.Nothing; the reaction will stay at equilibrium. B.The free energy of the system will change. C.Additional substrate will be formed. D.The reaction will change from endergonic to exergonic. E.Additional product will be formed.

Nothing; the reaction will stay at equilibrium.

Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description? A. Heat produced by the organism is conserved in the organism and not lost to the environment. B. Because energy must be conserved, organisms constantly recycle energy and thus need no input of energy. C. The metabolism of an organism is isolated from its surroundings. D. Organisms acquire energy from, and lose energy to, their surroundings. E. All of the listed responses are correct.

Organisms acquire energy from, and lose energy to, their surroundings.

Succinylcholine is structurally almost identical to acetylcholine. If succinylcholine is added to a mixture that contains acetylcholine and the enzyme that hydrolyzes acetylcholine (but not succinylcholine), the rate of acetylcholine hydrolysis is decreased. Subsequent addition of more acetylcholine restores the original rate of acetylcholine hydrolysis. Which of the following correctly explains this observation? A. The activation energy barrier for succinylcholine hydrolysis is higher than for acetylcholine hydrolysis. B. Succinylcholine must be a noncompetitive inhibitor. C. The active site must have the wrong configuration to permit succinylcholine binding. D. Succinylcholine must be a competitive inhibitor with acetylcholine. E. Succinylcholine must be an allosteric regulator for this enzyme.

Succinylcholine must be a competitive inhibitor with acetylcholine.

Which of these statements about enzyme inhibitors is true? A. A competitive inhibitor binds to the enzyme at a place that is separate from the active site. B. A noncompetitive inhibitor does not change the shape of the active site. C. Inhibition of enzyme function by compounds that are not substrates is something that only occurs under controlled conditions in the laboratory. D. The action of competitive inhibitors may be reversible or irreversible. E. When the product of an enzyme or an enzyme sequence acts as its inhibitor, this is known as positive feedback.

The action of competitive inhibitors may be reversible or irreversible.

Which of the following statements about the active site of an enzyme is correct? A. The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits. B. The active site has a fixed structure (shape). C. The active site allows the reaction to occur under the same environmental conditions as the reaction without the enzyme. D. Coenzymes are rarely found in the active site of an enzyme. E. The structure of the active site is not affected by changes in temperature.

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions? A. The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water. B. All types of cellular respiration produce ATP. C. Cellular respiration releases some energy as heat. D. The first and second choices are correct. E. The first, second, and third choices are correct.

The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.

The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs? A. The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site. B. The allosteric inhibitor binds to the active site, preventing the substrate from binding. C. The allosteric inhibitor lowers the temperature of the active site. D. The allosteric inhibitor binds to the substrate and prevents it from binding at the active site. E. The allosteric inhibitor causes free energy change of the reaction to increase.

The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.

According to the second law of thermodynamics, which of the following is true? A. The entropy of the universe is constantly decreasing. B. The total amount of energy in the universe is constant. C. Energy conversions increase the order in the universe. D. All reactions produce some heat. E. The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.

The decrease in entropy associated with life must be compensated for by increased entropy in the environment in which life exists.

What is meant by the "induced fit" of an enzyme? A. The enzyme structure is altered so that it can be induced to fit many different types of substrate. B. The presence of the substrate in solution induces the enzyme to slightly change its structure. C. The enzyme changes its shape slightly as the substrate binds to it. D. The substrate can be altered so that it is induced to fit into the enzyme's active site. E. The shape of the active site is nearly perfect for specifically binding the enzyme's substrate(s).

The enzyme changes its shape slightly as the substrate binds to it.

Which of the following statements correctly describe(s) the role(s) of heat in biological reactions? A. Heat from the environment is necessary for substrates to get over the activation energy barrier. B. The kinetic energy of the substrates is increased as the amount of heat in the system is increased. C. Increasing the amount of heat in a system will increase the rate of enzyme-catalyzed reactions. D. The first and second choices are correct. E. The second and third choices are correct.

The first and second choices are correct.

Above a certain substrate concentration, the rate of an enzyme-catalyzed reaction drops as the enzymes become saturated. Which of the following would lead to a faster conversion of substrate into product under these saturated conditions? A. an increase in concentration of enzyme B. increasing the temperature by a few degrees C. increasing the substrate concentration D. The first and second listed responses are correct. E. The first, second, and third listed responses are correct.

The first and second listed responses are correct.

Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium? A. the continuous removal of the products of a pathway to be used in other reactions B. an input of free energy from outside the pathway C. an input of heat from the environment D. The first and second listed responses are correct. E. The first, second, and third listed responses are correct.

The first and second listed responses are correct.

From the equation ΔG = ΔH - TΔS it is clear that _____. A. a decrease in the system's total energy will B. increase the probability of spontaneous change C. increasing the entropy of a system will increase the probability of spontaneous change D. increasing the temperature of a system will increase the probability of spontaneous change E. The first and second choices are correct. F. The first three choices are correct.

The first three choices are correct.

What best characterizes the role of ATP in cellular metabolism? A. The DG associated with its hydrolysis is positive. B. The release of free energy during the hydrolysis of ATP heats the surrounding environment. C. The charge on the phosphate group of ATP tends to make the molecule very water-soluble. D. The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate. E. It is catabolized to carbon dioxide and water

The free energy released by ATP hydrolysis may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

Molecules A and B contain 110 kcal/mol of free energy and molecules B and C contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded? A. A and B will be converted to C and D with a net release of energy. B. The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants. C. The conversion of A and B to C and D is exergonic; the products are less organized than the reactants. D. The conversion of A and B to C and D is spontaneous. E. The entropy in the products, C and D, is higher than in the reactants, A and B.

The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.

Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient? A. The hydrolysis of ATP is endergonic, and the active transport is exergonic. B. ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane. C. This is an example of energy coupling. D. Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system. E. Neither ATP hydrolysis nor active transport is spontaneous.

This is an example of energy coupling.

Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second law of thermodynamics? A. The process of photosynthesis produces energy that the plant uses to grow. B. The entropy of the universe must decrease to account for the increased entropy associated with plant growth. C. Growth of the crops must occur spontaneously. D. To obey the first law, the crops must represent an open system. E. All of the listed responses are correct.

To obey the first law, the crops must represent an open system.

Which of the following has the most free energy per molecule? A. a fatty acid molecule B. a starch molecule C. an amino acid molecule D. a cholesterol molecule E. a sugar molecule

a starch molecule

If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to A. add more substrate. B. heat the solution to 90°C. C. add more of the enzyme. D. add a noncompetitive inhibitor. E. add an allosteric inhibitor.

add more of the enzyme.

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of _____. A. noncompetitive inhibition B. allosteric regulation C. competitive inhibition D. feedback inhibition E. cooperativity

allosteric regulation

How do enzymes lower activation energy? A. The first two responses above are correct. B. by locally concentrating the reactants C. by increasing reactivity of products D. by harnessing heat energy to drive the breakage of bonds between atoms E. The second and third choices above are correct.

by locally concentrating the reactants

Which of the following reactions would be endergonic? A. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O B. ATP → ADP + Pi C. glucose + fructose → sucrose D. HCl → H+ + Cl- E. All of the listed responses are correct.

glucose + fructose → sucrose

Enzyme activity is affected by pH because _____ A. most substrates don't function well at high or low pH B. low pH will denature all enzymes C. changes in pH can cause loss of cofactors from the enzyme D. the binding of hydrogen ions to the enzyme absorbs energy and thus there may not be enough energy to overcome the activation energy barrier E. high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

The electronic arrangement in which of the following molecules means that this (these) molecule(s) has/have greater free energy than the others? A. methane B. carbon dioxide C. water D. The first two molecules listed are roughly equal in the energy they contain. E. The first three molecules listed are roughly equal in the energy they contain.

methane

Which of the following is an example of the cellular work accomplished with the free energy derived from the hydrolysis of ATP, involved in the production of electrochemical gradients? A. the chemical synthesis of ATP B. chromosome movement on microtubules C. facilitated diffusion D. the beating of cilia E. proton movement against a gradient of protons

proton movement against a gradient of protons

An exergonic (spontaneous) reaction is a chemical reaction that _____. A. is common in anabolic pathways B. cannot occur outside of a living cell C. leads to a decrease in the entropy of the universe D. releases energy when proceeding in the forward direction E. occurs only when an enzyme or other catalyst is present

releases energy when proceeding in the forward direction

In general, the hydrolysis of ATP drives cellular work by _____. A. releasing free energy that can be coupled to other reactions B. lowering the free energy of the reaction C. changing to ADP and phosphate D. acting as a catalyst E. releasing heat

releasing free energy that can be coupled to other reactions

Most cells cannot harness heat to perform work because A. heat is not a form of energy. B. heat can never be used to do work. C. cells do not have much heat; they are relatively cool. D. temperature is usually uniform throughout a cell. E. heat must remain constant during work.

temperature is usually uniform throughout a cell.

Which of the following is changed by the presence of an enzyme in a reaction? A, the G value for the products B. the magnitude of ΔG. C. the G value for the reactants D. the activation energy E. The sign of ΔG

the activation energy

Which of the following situations does not represent an energy transformation? A. the production of ATP using phosphate from the breakdown of glucose B. the production of sugars from carbon dioxide and water during photosynthesis C. the release of carbon dioxide as glucose is broken down during cellular respiration D. the coupling of ATP hydrolysis to the production of a proton gradient across a membrane by a proton pump E. All of the listed responses represent energy transformations.

the coupling of ATP hydrolysis to the production of a proton gradient across a membrane by a proton pump

Which of the following determines the sign of ΔG for a reaction? A. the enzyme catalyzing the reaction having a high affinity (strength of binding) for the reactants B. the free energy of the reactants and the free energy of the products C. the free energy of the products D. the enzyme catalyzing the reaction having a low affinity for the products E. the free energy of the reactants

the free energy of the reactants and the free energy of the products

The formation of glucose-6-phosphate from glucose is an endergonic reaction and is coupled to which of the following reactions or pathways? A. the active transport of a phosphate ion into the cell B. the hydrolysis of ATP C. the conversion of glucose + fructose to make sucrose D. the contraction of a muscle cell E. the formation of ATP from ADP + Pi

the hydrolysis of ATP

Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because _____. A. the phosphate groups are polar and are attracted to the water in the cell's interior B. the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP C. they are hydrogen bonds, which are only about 10% as strong as covalent bonds D. the bonds between the phosphate groups are unusually strong and breaking them releases free energy E. the valence electrons in the phosphorus atom have less energy on average than those of other atoms

the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP

A chemical reaction is designated as exergonic rather than endergonic when _____. A. activation energy is required B. the potential energy of the products is less than the potential energy of the reactants C. activation energy exceeds net energy release D. the products are less complex than the reactants E. it absorbs more energy

the potential energy of the products is less than the potential energy of the reactants

Some bacteria are metabolically active in hot springs because A. they are able to maintain a lower internal temperature. B. their enzymes have high optimal temperatures. C. high temperatures make catalysis unnecessary. D. they use molecules other than proteins or RNAs as their main catalysts. E. their enzymes are completely insensitive to temperature.

their enzymes have high optimal temperatures.

A plot of reaction rate (velocity) against temperature for an enzyme indicates little activity at 10°C and 45°C, with peak activity at 35°C. The most reasonable explanation for the low velocity at 10°C is that _____. A. the cofactors required by the enzyme system lack the thermal energy required to activate the enzyme B. the enzyme was denatured C. the hydrogen bonds that define the structure of the enzyme's active site are unstable D. the substrate becomes a competitive inhibitor at lower temperature E. there is too little activation energy available

there is too little activation energy available

If, during a process, the system becomes more ordered, then _____. A. ΔH is negative B. ΔH is positive C. ΔG is positive D. ΔS is negative E. ΔG is negative

ΔS is negative

When one molecule is broken down into six component molecules, which of the following will always be true? A. ΔH is negative. B. An input of free energy is needed. C. ΔG is positive. D. ΔS is negative. E. ΔS is positive.

ΔS is positive.