Biology in Focus: Chapter 7 Cellular Respiration

Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?

Carbon dioxide

Which step of the cellular respiration pathway can take place in the absence of oxygen?

Glycolysis

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.

True or false? The potential energy in an ATP molecule is derived mainly from its three phosphate groups.

True

True or false? The reactions that generate the largest amounts of ATP during cellular respiration take place in the mitochondria.

True

Which of the following normally occurs regardless of whether or not oxygen (O2) is present?

glycolysis

Which of the following processes takes place in the cytosol of a eukaryotic cell?

glycolysis

Which of the following occurs in the cytosol of a eukaryotic cell?

glycolysis and fermentation

Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells?

mitochondrial intermembrane space

During aerobic respiration, H2O is formed. Where does the oxygen atom for the formation of the water come from?

molecular oxygen (O2)

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation

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

substrate-level phosphorylation

In glycolysis there is a net gain of _____ ATP.

2

Starting with one molecule of glucose, the energy-containing products of glycolysis are _____.

2 NADH, 2 pyruvate, and 2 ATP

In glycolysis, what starts the process of glucose oxidation?

ATP

Which energy-rich molecule produced by cellular respiration directly powers cell work?

ATP

The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP. 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.

In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of _____.

ATP, CO2, and ethanol (ethyl alcohol)

The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATP during oxidative phosphorylation. Phosphorylation reactions involve the addition of a phosphate group to another molecule. Select the statement that correctly describes substrate-level phosphorylation in glycolysis.

An enzyme transfers a phosphate group from one molecule (an intermediate in the breakdown of glucose to pyruvate) to ADP to form ATP. This is very different from the mechanism of ATP synthesis that takes place in oxidative phosphorylation.

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.

What is the correct general equation for cellular respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP energy

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 stage of glucose metabolism produces the most ATP?

Electron transport and chemiosmosis

What best describes the electron transport chain?

Electrons are passed from one carrier to another, releasing a little energy at each step.

During aerobic respiration, what molecule directly donates electrons to the electron transport chain at the lowest energy level?

FADH2

Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell?

Fermentation

Which molecule is metabolized in a cell to produce energy for performing work?

Glucose

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 immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the

H+ concentration across the membrane holding ATP synthase.

Why is glycolysis considered to be one of the first metabolic pathways to have evolved?

It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms.

In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve?

It increases the surface for oxidative phosphorylation.

A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?

It is stored in NADH and FADH2

The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?

Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.

Which of the following statements about NAD+ is true?

NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle.

Following glycolysis and the citric acid cycle, but before the electron transport chain and oxidative phosphorylation, the carbon skeleton of glucose has been broken down to CO2 with some net gain of ATP. Most of the energy from the original glucose molecule at that point in the process, however, is in the form of _____.

NADH

What molecule is oxidized in the following reaction? Pyruvate + NADH + H+ → Lactate + NAD+

NADH

Which of the following statements about the electron transport chain is true?

NADH and FADH2 donate their electrons to the chain.

What is the role of oxygen in cellular respiration?

Oxygen accepts high-energy electrons after they are stripped from glucose.

In preparing pyruvate to enter the citric acid cycle, what 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.

In cellular respiration, a series of molecules forming an electron transport chain alternately accepts and then donates electrons. What is the advantage of such an electron transport chain?

The advantage of an electron transport chain is that a small amount of energy is released with the transfer of an electron between each pair of intermediates.

Which of the following statements about the chemiosmotic synthesis of ATP is correct?

The chemiosmotic synthesis of ATP requires that the electron transport in the inner mitochondrial membrane be coupled to proton transport across the same membrane.

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.

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

The products of glycolysis contain the same total number of carbon atoms as in the starting material.

Which one of the following statements about the redox reactions of the electron transport chain is correct?

The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.

Which statement describes glycolysis?

This process splits glucose in half and produces 2 ATPs for each glucose.

Which statement describes the electron transport chain?

This process uses energy captured from electrons flowing to oxygen to produce most of the ATPs in cellular respiration.

The oxygen consumed during cellular respiration is involved directly in which process or event?

accepting electrons at the end of the electron transport chain

Which one of the following is formed by the removal of a carbon (as CO2) from a molecule of pyruvate?

acetyl CoA

The primary role of oxygen in cellular respiration is to _____.

act as an acceptor for electrons and hydrogen, forming water

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 _____.

an endergonic reaction coupled to an exergonic reaction

In chemiosmosis, what is the most direct source of energy that is used to convert ADP + i to ATP?

energy released from movement of protons through ATP synthase, down their electrochemical gradient

The function of cellular respiration is to __________.

extract usable energy from glucose

What molecule is broken down in cellular respiration, providing fuel for the cell?

glucose

Glycolysis is the multi-step breakdown of _____. Several different _____ play a role in this process.

glucose ... enzymes

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

glucose ... oxygen

During aerobic respiration, electrons travel downhill in which sequence?

glucose → NADH → electron transport chain → oxygen

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

glycolysis

Correct sequence of steps as energy is extracted from glucose during cellular respiration.

glycolysis → pyruvate→ pyruvate oxidation →acetyl CoA → citric acid cycle → electron transport chain

Substrate-level phosphorylation occurs _____.

in both glycolysis and the citric acid cycle

Unlike the Citric Acid cycle and electron transport, glycolysis occurs _____.

in the cytoplasm

The electron transport chain _____.

is a series of redox reactions

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 what compounds?

lactate

In muscle cells, fermentation produces _____.

lactate and NAD+

A molecule becomes more oxidized when it __________.

loses an electron

The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction _____.

loses electrons and loses potential energy

In what organelle would you find acetyl CoA formation, the citric acid cycle, and the electron transport chain?

mitochondrion

Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?

oxidation of pyruvate to acetyl CoA and the citric acid cycle

When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes _____.

oxidized

The final electron acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is

oxygen.

Cellular respiration requires fuel (glucose) and oxygen gas. The main process that produces these inputs is _____.

photosynthesis

In mitochondria, exergonic redox reactions

provide the energy that establishes the proton gradient.

In fermentation _____ is reduced and _____ is oxidized.

pyruvate ... NADH

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

pyruvate, ATP, and NADH

When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes _____.

reduced

When electrons move closer to a more electronegative atom, what happens? The more electronegative atom is ____ and _____________.

reduced; energy is released

Cellular respiration accomplishes two major processes: (1) it breaks glucose down into smaller molecules, and (2) it harvests the chemical energy released and stores it in ATP molecules. By the end of _____, the breakdown of glucose is complete; most ATP molecules are produced during _____.

the Citric Acid cycle ... electron transport chain

Which part(s) of cellular respiration take(s) place in the mitochondria?

the Citric Acid cycle and the electron transport chain

Most of the CO2 from the catabolism of glucose is released during _____.

the citric acid cycle

Most CO2 from catabolism is released during

the citric acid cycle.

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

the cytosol

What event takes place in the electron transport chain?

the extraction of energy from high-energy electrons remaining from glycolysis and the citric acid cycle

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

the inner membrane of the mitochondrion

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 in a chemical form that cells can use for work

In electron transport, high-energy electrons "fall" to oxygen through a series of reactions. The energy released is used to _____.

transport protons into the intermembrane space of the mitochondria, where they become concentrated. They then flow back out into the the inner compartment (matrix) of the mitochodria. On the way back, protons turn ATP synthase turbines and produce ATP.

In glycolysis, for each molecule of glucose oxidized to pyruvate _____.

two molecules of ATP are used and four molecules of ATP are produced.

What is/are the most important output(s) of glycolysis?

two pyruvates and two NADH molecules