CHAPTER 9: Cellular Respiration & Fermentation

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2; intermembrane space (The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and used to pump hydrogen ions into the intermembrane space.)

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

Which of these is NOT a product of the citric acid cycle?

acetyl CoA (Acetyl CoA enters the citric acid cycle.)

Which of these enters the citric acid cycle?

acetyl CoA (Acetyl CoA is a reactant in the citric acid cycle.)

The synthesis of ATP by oxidative phosphorylation, using the energy released by movement of protons across the membrane down their electrochemical gradient, is an example of which of the following processes?

coupling of an endergonic reaction to an exergonic reaction

The function of cellular respiration is to __________.

extract usable energy from glucose

The final electron acceptor of cellular respiration is _____.

Oxygen (Oxygen is combined with electrons and hydrogen to form water.)

A molecule becomes more oxidized when it __________.

loses an electron

If glucose is the sole energy source, what fraction of the carbon dioxide exhaled by animals is generated only by the reactions involved in oxidation of pyruvate to acetyl CoA?

1/3

Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis?

100%

How many NADH are produced by glycolysis?

2

In glycolysis there is a net gain of _____ ATP.

2

For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.

2 (Each glucose produces two pyruvates, each of which is converted into acetyl CoA.)

For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle?

4

For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.

6 (3 NADH + H+ are produced per each acetyl CoA that enters the citric acid cycle.)

During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages. Drag the labels from the left (which represent numbers of carbon atoms) onto the diagram to identify the number of carbon atoms in each intermediate in acetyl CoA formation and the citric acid cycle.

A) 2 C B) 6 C C) 6 C D) 5 C E) 4 C F) 4 C G) 4 C H) 4 C I) 4 C

In glycolysis, what starts the process of glucose oxidation?

ATP

Most of the ATP in cellular respiration is produced by the process of chemiosmosis. How does this process produce ATP?

H+ flows across the inner mitochondrial membrane through the enzyme ATP synthase.

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Which of these statements is the correct explanation for this observation?

In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.

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

NADH

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle. Drag each compound to the appropriate bin. If a compound is not involved in the citric acid cycle, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of the citric acid cycle are included.)

Net Input: Acetyl CoA, NAD⁺, ADP Net Output: Coenzyme A, CO₂, NADH, ATP Not Input or Output: Pyruvate, Glucose, O₂

All of the processes involved in cellular respiration produce ATP. Which of the following processes produces the most ATP?

Oxidative phosphorylation

Which part of the catabolism of glucose by cellular respiration requires molecular oxygen (O2) and produces CO2?

The combination of the citric acid cycle and electron transport

Which of the following metabolic pathways produce(s) the most ATP, per glucose molecule metabolized, during cellular respiration?

The electron transport chain and oxidative phosphorylation

The energy from the electrons in NADH and FADH2 fuel what process in the electron transport chain?

The pumping of H+ across the cristae of the mitochondrion

What is the total production of ATP, NADH, and FADH2 in the citric acid cycle from one molecule of glucose?

Two ATP, six NADH, and two FADH2

The oxygen consumed during cellular respiration is directly involved in which of the following processes or events?

accepting electrons at the end of the electron transport chain

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+

During the energy investment phase of glycolysis, __________.

glucose is phosphorylated before it is split into two three-carbon molecules

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

glucose; oxygen

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation (This process utilizes energy released by electron transport.)

During the energy payoff phase of glycolysis, __________.

NADH and ATP are produced

In what molecule(s) is the majority of the chemical energy from pyruvate transferred during the citric acid cycle?

NADH and FADH2

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors. Drag the labels on the left to show the net redox reaction in acetyl CoA formation and the citric acid cycle. Note that two types of electron carriers are involved.

A) CO2 B) NADH C) FAD D) FADH2

The four stages of cellular respiration do not function independently. Instead, they are coupled together because one or more outputs from one stage functions as an input to another stage. The coupling works in both directions, as indicated by the arrows in the diagram below. In this activity, you will identify the compounds that couple the stages of cellular respiration. Drag the labels on the left onto the diagram to identify the compounds that couple each stage. Labels may be used once, more than once, or not at all.

A. pyruvate B. NADH C. NAD⁺ D. NADH E. NAD⁺

Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

Glucose is the primary fuel for cellular respiration. Which of the following molecules can also be used by cellular respiration to generate ATP?

Amino acids Glycerol Fatty acids

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

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)

Both electron transport and ATP synthesis would stop.

Which of the summary statements below describes the results of the following reaction? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy

C6H12O6 is oxidized and O2 is reduced.

A cell has enough available ATP to meet its needs for about 30 seconds. What is likely to happen when an athlete exhausts his or her ATP supply?

Catabolic processes are activated that generate more ATP.

Select the correct statement about cellular respiration.

Cellular respiration and breathing differ in that cellular respiration is at the cellular level, whereas breathing is at the organismal level.

Which of the following pairs of pathways and their location in the cell is incorrectly matched?

Citric acid cycle: cytosol

Which of these is NOT a product of glycolysis?

FADH2 (It is a product of the citric acid cycle.)

Cells must regulate their metabolic pathways so that they do not waste resources. What is the most common mechanism that regulates cellular respiration in most cells?

Feedback inhibition of glycolysis

Fermentation by itself produces no ATP but keeps glycolysis going, which produces a small amount of ATP. How does fermentation do this?

Fermentation oxidizes NADH to NAD+, which facilitates the production of ATP in glycolysis.

NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?

Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor.

In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced?

Glucose is consumed, and carbon dioxide is produced. (The carbon in glucose is oxidized to carbon dioxide during cellular respiration.)

During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?

Glucose utilization would increase a lot.

In which process is glucose oxidized to form two molecules of pyruvate?

Glycolysis

Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?

Glycolysis

Cellular locations of the four stages of cellular respiration Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy.

Glycolysis - Cytosol Acetyl CoA - Mitochondrial matrix Citric acid cycle - Mitochondrial matrix Oxidative phosphorylation - inner mitochondrial membrane

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.

What is the role of oxygen in the electron transport chain?

It is reduced to form water.

Match each product of pyruvate metabolism with the condition under which it is produced. Drag each item to the appropriate bin.

Lactate: fermentation in human muscle Ethanol: fermentation in yeast and bacteria Acetyl CoA: aerobic oxidation (In the presence of oxygen, human cells carry out aerobic respiration, which yields acetyl CoA. In the absence of oxygen, human cells can carry out lactic acid fermentation, which yields lactate. Yeasts and many bacteria carry out alcohol fermentation, which takes place under anaerobic conditions, and produces ethanol)

Which statement correctly describes the difference between alcohol fermentation and lactic acid fermentation?

Lactic acid fermentation produces lactate, and alcohol fermentation produces ethanol.

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis. Drag each compound to the appropriate bin. If the compound is not involved in glycolysis, drag it to the "not input or output" bin.

Net Input: ADP, NAD⁺, Glucose Net Output: ATP, NADH and Pyruvate, not input or output: O₂, CO₂, coenzyme A and acetyl CoA

In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation. Drag each compound to the appropriate bin. If a compound is not involved in oxidative phosphorylation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of oxidative phosphorylation are listed.)

Net Input: NADH, ADP, O₂ Net Output: NAD⁺, ATP, CO₂ and Water Not Input or Output: Pyruvate, Glucose, Acetyl CoA, Coenzyme A and CO₂.

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation. Drag each compound to the appropriate bin. If a compound is not involved in acetyl CoA formation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of acetyl CoA formation are included.)

Net Input: NAD⁺, coenzyme A, pyruvate Net Output: NADH, acetyl CoA, CO₂ not input or output: O₂, ADP, glucose and ATP

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

Oxidation of glucose to pyruvate; oxidation of pyruvate; oxidation of acetyl-coA; oxidative phosphorylation

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

Pyruvate is oxidized and decarboxylated, and the removed electrons are used to reduce an NAD+ to an NADH.

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

Reducing NAD+ to NADH in glycolysis and the citric acid cycle AND producing a proton gradient for ATP synthesis in the mitochondria.

Identify all correct statements about the basic function of fermentation.

The basic function of fermentation is the regeneration of NAD+, which allows continued ATP production by glycolysis. (Fermentation occurs in the absence of oxygen and does not yeild as much ATP. Read about fermentation.)

Most of the NADH that delivers electrons to the electron transport chain comes from which of the following processes?

The citric acid cycle

The ATP synthase in a human cell obtains energy for synthesizing ATP directly from which of the following processes?

The flow of H+ across the inner mitochondrial membrane through the ATP synthase enzyme

Which of the following statements accurately describes the function of a metabolic pathway involved in cellular respiration?

The function of glycolysis is to begin catabolism by breaking glucose into two molecules of pyruvate, with a net yield of two ATP. (Glycolysis is the first stage in cellular respiration and does not depend on the presence of oxygen.)

The proximate (immediate) source of energy for oxidative phosphorylation is _____.

kinetic energy that is released as hydrogen ions diffuse down their concentration gradient (Concentration gradients are a form of potential energy.)

Sort the following items according to whether they are reactants or products in the anaerobic reduction of pyruvate during lactic acid fermentation. Drag each item to the appropriate bin.

reactants: pyruvate, NADH Products: lactate, NAD+ (When an animal engages in strenuous usage of its muscles, anaerobic conditions ensue, and pyruvate is reduced to lactate. In the process, NADH is oxidized to NAD+. This NAD+ can further oxidize glyceraldehyde-3-phosphate to produce more ATP.)

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

regenerate NAD+

When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.) Sort the labels into the correct bin according to the effect that gramicidin would have on each process.

remains the same: proton pumping rate, electron transport rate, rate of oxygen uptake decreases or goes to zero: rate of ATP synthesis, size of protein gradient

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation

In the citric acid cycle, ATP molecules are produced by _____.

substrate-level phosphorylation (A phosphate group is transferred from GTP to ADP.)

In mitochondrial electron transport, what is the direct role of O2?

to function as the final electron acceptor in the electron transport chain

Which of the following best describes the main purpose of the combined processes of glycolysis and cellular respiration?

transforming the energy in glucose and related molecules into a chemical form that cells can use for work (The energy made available during cellular respiration is coupled to a production of ATP, the basic energy currency that cells use for work.)