BIOLOGY CH 9 Practice Test

The overall efficiency of respiration (the percentage of the energy released that is saved in ATP) is approximately

35% Correct. The efficiency of respiration is 7.3 kcal per mole times 32 moles (maximum ATP yield per mole of glucose) divided by 686 kcal (the amount of energy contained in one mole of glucose), or about 35%.

How many molecules of ATP are gained by substrate-level phosphorylation from the complete breakdown of a single molecule of glucose in the presence of oxygen?

4 Correct. There is a net gain of two ATP from glycolysis and one from each molecule of acetyl CoA oxidized in the citric acid cycle for a total of four per glucose.

If a compound that allows protons to freely diffuse across membranes is added to cells that are actively metabolizing glucose via cellular respiration, which of the following processes would stop?

None of the listed responses is correct. Correct. The chemiosmotic synthesis of ATP would stop in the mitochondria, but substrate-level phosphorylation could continue.

After completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of

NADH Correct. The citric acid cycle produces three NADH per turn of the cycle.

Which of the following is the process in which glucose is oxidized to generate two molecules of pyruvate, and in which ATP and NADH are produced?

None of the listed responses is correct. Correct. The name of the process that oxidizes glucose to pyruvate and produces ATP and NADH is glycolysis.

In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs?

Pyruvate is oxidized and a molecule of carbon dioxide is removed. The electrons removed in this process are used to reduce NAD+ to NADH. Correct. In addition to these events, a molecule of coenzyme A is attached to the resulting acetyl group

Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step

enables the cell to recycle the reduced NADH to oxidized NAD+ Correct. Normally, the reduced NADH delivers its electrons to the electron transport chain, enabling NAD+ to be recycled to glycolysis.

The function of cellular respiration is to

extract usable energy from glucose Correct. The most efficient pathway for ATP generation is cellular respiration, in which oxygen is consumed as a reactant, along with the organic fuel (frequently glucose).

Which of the following represents the major (but not the only) energy accomplishment of the citric acid cycle?

formation of NADH and FADH2 Correct. Each turn of the citric acid cycle releases carbon dioxide, forms one ATP by oxidative phosphorylation, and passes electrons to three NAD+ and one FAD.

Which of the following molecules in the process of glycolysis possesses the most chemical energy?

fructose-1,6-bisphosphate Correct. Fructose-1,6-bisphosphate has received two phosphate groups from ATP, conserving some of the energy derived from the hydrolysis of ATP in the fructose-1, 6-bisphosphate molecule.

In the overall process of glycolysis and cellular respiration, __________ is oxidized and __________ is reduced.

glucose ... oxygen Correct. In cellular respiration, electrons and hydrogen are removed from glucose and added to oxygen.

Of the metabolic pathways listed below, which is the only pathway found in all organisms?

glycolysis Correct. Ancient prokaryotes probably used glycolysis to make ATP long before oxygen was present in Earth's atmosphere. Glycolysis is the most widespread metabolic pathway.

A chemist has discovered a drug that blocks phosphoglucoisomerase, an enzyme that catalyzes the second reaction in glycolysis. He wants to use the drug to kill bacteria in people with infections. However, he cannot do this because

human cells must also perform glycolysis; the drug might also poison them Correct. The chemist's drug could have a devastating effect on human cells.

Sports physiologists at an Olympic training center wanted to monitor athletes to determine at what point their muscles were functioning anaerobically. They could do this by checking for a buildup of which of the following compounds?

lactate Correct. In humans, muscle cells switch to lactate fermentation after becoming anaerobic.

Which of the following is a correct description of the events of cellular respiration in proper sequence?

oxidation of glucose to pyruvate; oxidation of pyruvate; citric acid cycle; oxidative phosphorylation Correct. This is the correct sequence of events in cellular respiration.

Most of the ATP produced in cellular respiration comes from which of the following processes?

oxidative phosphorylation Correct. After hydrogen ions are pumped into the mitochondrial intermembrane space, they flow back through ATP synthase, which produces most of the ATP associated with cellular respiration.

Which of the following events accompanies the conversion of pyruvate to acetyl CoA before the citric acid cycle?

release of CO2 and synthesis of NADH Correct. The carboxyl group of pyruvate is removed as a carbon dioxide molecule. The remaining two-carbon fragment is oxidized to acetate and NAD+ is reduced to NADH.

Which of the following processes generates most of the NADH that delivers electrons to the electron transport chain?

the citric acid cycle Correct. Most of the NADH is produced during the citric acid cycle, along with some FADH2.

Where do the reactions of glycolysis occur in a eukaryotic cell?

the cytosol Correct. Glycolysis occurs in the cytosol.

Energy for synthesizing ATP is obtained by ATP synthase directly from which of the following processes?

the flow of H+ across the inner mitochondrial membrane through the ATP synthase enzyme Correct. Hydrogen ions flow along an electrochemical gradient across the inner mitochondrial membrane. The gradient is the source of the energy for ATP production.

In eukaryotic cells, the components of the electron transport chain are located in or on

the inner membrane of the mitochondrion Correct. The electron transport chain is an energy converter that uses the exergonic flow of electrons to pump hydrogen ions across the membrane from matrix to intermembrane space.

Where do the reactions of the citric acid cycle occur in eukaryotic cells?

the matrix of the mitochondrion Correct. The citric acid cycle, which takes place in the mitochondrial matrix, completes the degradation of glucose.

Oxygen gas (O2) is one of the strongest oxidizing agents known. The explanation for this is that

the oxygen atom is very electronegative Correct. The high electronegativity of the oxygen atom is the reason that oxygen is such a strong oxidizing agent.

In brewing beer, maltose (a disaccharide of glucose) is

the substrate for alcoholic fermentation Correct. In alcoholic fermentation, maltose is cleaved into two glucose molecules, which undergo glycolysis. The resulting pyruvate is converted to ethanol in two steps, one of which regenerates the supply of NAD+ needed for continued glycolysis.

A small amount of ATP is made in glycolysis by which of the following processes?

transfer of a phosphate group from a fragment of glucose to ADP by substrate-level phosphorylation Correct. Remember that glucose is phosphorylated at the beginning of glycolysis.

Which of the following best describes the electron transport chain?

Electrons are passed from one carrier to another, releasing a little energy at each step. Correct. NADH and FADH2 deliver electrons from the breakdown products of glycolysis and the citric acid cycle to the electron transport chain, which passes these electrons from one molecule to another, releasing a small amount of energy at each step.

A gram of fat oxidized by respiration produces approximately twice as much ATP as a gram of carbohydrate. Which of the following best explains this observation?

Fats are better electron donors to oxygen than are sugars. Correct. Fats contain more hydrogen and less oxygen than sugars—it is the transfer of electrons from good donors such as hydrogen atoms to good acceptors such as oxygen that provides the energy in respiration.

Each ATP molecule contains about 1% of the amount of chemical energy available from the complete oxidation of a single glucose molecule. Cellular respiration produces about 32 ATP from one glucose molecule. What happens to the rest of the energy in glucose?

It is converted to heat. Correct. The process is only about 38% efficient, with the rest of the energy lost as heat.

When solid tumors of animals reach a certain size, the center of the tumor begins to die. To prevent this, the tumor can recruit new blood vessels. What purpose does the recruitment of blood vessels to growing tumors serve?

It supplies oxygen so that aerobic cellular respiration can occur instead of fermentation, and it supplies glucose to the rapidly dividing cells of the tumor. Correct. The new blood vessels provide the fuel for cellular respiration: oxygen and glucose. The new blood vessels also eliminate wastes such as carbon dioxide from the tumor. Some anti-cancer drugs attempt to block the process of recruitment of new blood vessels to tumors.

In glycolysis in the absence of oxygen, cells need a way to regenerate which compound?

NAD+ Correct. The NAD+ needs to be regenerated, which is why ethanol or lactate is formed

When a poison such as cyanide blocks the electron transport chain, glycolysis and the citric acid cycle also eventually stop working. Which of the following is the best explanation for this?

NAD+ and FAD are not available for glycolysis and the citric acid cycle to continue. Correct. Unless the electron transport molecules (NADH and FADH2) can recycle back to their oxidized states (NAD+ and FAD), they will be unable to receive electrons in the other steps of cellular respiration.

Which of the following statements is the best explanation of what happens to the temperature and carbon dioxide concentration during a 1-hour class period in a classroom of 300 students if the heating and air conditioning is turned off and all doors are kept closed?

Temperature and the level of carbon dioxide rise as heat and carbon dioxide are by-products of cellular respiration. Correct. The oxidation of organic molecules produces carbon dioxide, and as the exergonic process of cellular respiration is not 100% efficient, some energy is lost to the environment as heat.

If muscle cells in the human body consume O2 faster than it can be supplied, which of the following is likely to result?

The first three answers are correct. Correct. Muscle cells would not be able to produce enough ATP to meet demands, oxidative phosphorylation would stop, and muscle cells would consume glucose at an increased rate.

If significant amounts of materials are removed from the citric acid cycle to produce amino acids for protein synthesis, which of the following will result?

The first three answers are correct. Correct. The first three answers are correct.

Which of the following substances is/are involved in oxidative phosphorylation?

The first three listed substances are involved in oxidative phosphorylation. Correct. ADP is converted to ATP during oxidative phosphorylation, and oxygen functions as the terminal electron acceptor in oxidative phosphorylation.

Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

The first two choices are correct. Correct. Electrons from oxidation of glucose are used to reduce NAD+ and produce a proton gradient for ATP synthesis in the mitochondria.

Why is the citric acid cycle called a "cycle"?

The four-carbon acid that accepts the acetyl CoA in the first step of the cycle is regenerated by the last step of the cycle. Correct. The cycling referred to is that of the resynthesis of the four-carbon compound.

There is no production of carbon dioxide in glycolysis. Which of the following is the best explanation for this fact?

The products of glycolysis contain the same total number of carbon atoms as in the starting material. Correct. All of the carbon in one glucose molecule is accounted for in the two molecules of pyruvate produced by glycolysis.

When protein molecules are used as fuel for cellular respiration, __________ are produced as waste.

amino groups Correct. The amino group is a residual product of amino acid catabolism.

During aerobic respiration, molecular oxygen (O2) is used for which of the following purposes?

at the end of the electron transport chain to accept electrons and form H2O Correct. O2 is the final electron acceptor

In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive oxygen. The mice were closely monitored, and after a few minutes radioactive oxygen atoms showed up in

carbon dioxide Correct. One molecule of CO2 is formed when pyruvate is converted to acetyl CoA, and two molecules of CO2 are produced in the citric acid cycle.

BIOLOGY CH 9 Cellular Respiration and Fermentation Practice Test A molecule becomes more oxidized when it

loses an electron Correct. During oxidation, an electron is removed.

Which of the following is the source of the energy that produces the chemiosmotic gradient in mitochondria?

movement of electrons down the electron transport chain Correct. Energy from the flow of electrons along the electron transport chain is used to pump hydrogen ions (protons) across the inner mitochondrial membrane, creating the chemiosmotic gradient.

During the reaction C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, which compound is reduced as a result of the reaction?

oxygen Correct. In cellular respiration, glucose is oxidized (resulting in the production of carbon dioxide) and oxygen is reduced (resulting in the production of water).

The energy given up by electrons as they move through the electron transport chain is used in which of the following processes?

pumping H+ across a membrane Correct. Many of the electron transport molecules in the mitochondrion pump a hydrogen ion into the intermembrane space when they pass an electron along the chain.

Muscle tissues make lactate from pyruvate to do which of the following?

regenerate NAD+ Correct. Human muscle cells make ATP by lactic acid fermentation when oxygen is scarce. This allows them to regenerate NAD+ so that glycolysis can continue.

In the citric acid cycle, for each pyruvate that enters the cycle, one ATP, three NADH, and one FADH2 are produced. For each glucose molecule that enters glycolysis, how many ATP, NADH, and FADH2 are produced in the citric acid cycle?

two ATP, six NADH, two FADH2 Correct. Then the NADH and FADH2 go through the electron transport chain.