AP Biology 3.5 (Part 2)

Cellular Respiration

Scientists were interested in testing the effects of rotenone, a broad-spectrum pesticide, on a cell culture. Cell culture was used as a control, while culture was treated with rotenone. After a period of time, the scientists measured the concentration of several metabolites in the mitochondria of cells in both cultures. Their results are shown in the table below.

Metabolites	Concentration in Culture A (μM)	Concentration in Culture B (μM)
Pyruvate	25	25
NADH	55	550
NAD+	55	5
ATP	85	5
ADP + Pi	55	100
FADH2	25	26
FAD	25	25

Based on the data in the table, which of the following best explains the effects of rotenone on cellular respiration?

Responses

A

Rotenone acts as an inhibitor of the enzymes in the Krebs cycle.

B

NADH, produced during glycolysis, is not able to enter the mitochondria because transport proteins are blocked from entering.

C

Treated cells are not able to break down NADH because certain enzymes of the electron transport chain are inhibited.

D

Rotenone acts as an allosteric inhibitor of glycolytic enzymes, thus inhibiting cellular respiration.

Answer C

Correct. The data indicate that NADH concentrations are significantly increased in cell culture B.

Certain chemicals, including sodium fluoride (NaF), are capable of inhibiting specific steps of glycolysis. Figure 1 shows the steps of the glycolysis pathway, indicating where various macromolecules enter the pathway as well as the specific reaction inhibited by NaF.

Figure 1. Key steps in the metabolic pathway of glucose

Based on Figure 1, the net number of ATP molecules produced during glycolysis from the metabolism of a single glucose molecule is closest to which of the following?

Responses

A

0

B

2

C

4

D

8

Answer B

Correct. During glycolysis 4 ATP are generated, but 2 are converted to ADP in the process.

Certain chemicals, including sodium fluoride (NaF), are capable of inhibiting specific steps of glycolysis. Figure 1 shows the steps of the glycolysis pathway, indicating where various macromolecules enter the pathway as well as the specific reaction inhibited by NaF.

Figure 1. Key steps in the metabolic pathway of glucose

Tarui disease is an inherited disorder that is caused by mutations in PFKM, the gene that encodes a subunit of phosphofructokinase, an enzyme in the glycolysis pathway. Individuals with Tarui disease produce little or no functional phosphofructokinase in skeletal muscle cells. Based on Figure 1, which of the following best explains why a low carbohydrate diet is recommended for those with Tarui disease?

Responses

A

Carbohydrates are capable of undergoing lactic acid fermentation, and amino acids and fatty acids are not.

B

Carbohydrate metabolism requires all the reactions of glycolysis, and amino acids and fatty acids do not.

C

Carbohydrates cannot be used to synthesize important metabolic enzymes like amino acids and fatty acids can be.

D

Carbohydrates cannot be stored, while amino acids and fatty acids can be.

Answer B

Correct. Noncarbohydrates can provide energy to a cell through other metabolic pathways.

Researchers conducted an experiment to investigate the effects of a valinomycin treatment on skeletal muscle cells. Valinomycin is a naturally occurring substance that can be used as a drug. The results of the experiment are presented in the table.

	Relative Rates of Production
Time after Treatment	Untreated Cells	Valinomycin-Treated Cells
5 minutes	1.0	0.3
10 minutes	7.7	2.7

Which of the following claims about the effects of the valinomycin treatment is best supported by the data presented in the table?

Responses

A

The valinomycin treatment caused an increase in the activity of the rough endoplasmic reticulum.

B

The valinomycin treatment caused an increase in the activity of the Golgi complex.

C

The valinomycin treatment caused a decrease in the activity of the lysosome.

D

The valinomycin treatment caused a decrease in the activity of the mitochondria.

Answer D

Correct. The data indicate that the valinomycin treatment caused a decrease in the relative rate of ATP production, which likely resulted from impaired mitochondrial function.

Students in a class measured the mass of various living organisms. They then kept the organisms in the dark for 24 hours before remeasuring them. None of the organisms were provided with nutrients during the 24-hour period. The data are as follows.

Which of the following is the best explanation for the pattern of change in mass of the organisms over time?

Responses

A

Water loss due to evaporation

B

Cellular respiration

C

The law of conservation of matter

D

Growth and reproduction

B

Cellular respiration

The electron transport chain (ETC) is made up of several carrier molecules that transport electrons. These carrier molecules are found within membranes.

Which of the following statements best explains why these carrier molecules are typically found within membranes?

Responses

A

The electrons that move through the ETC are directly used to drive the processes of endocytosis and exocytosis.

B

The electrons that move through the ETC are coupled with the pumping of ATP out of the intermembrane space.

C

The energy derived from the ETC creates a difference in the concentration of protons on either side of the membrane.

D

The energy derived from the ETC is used to fully oxidize an ATP molecule, releasing stored energy outside the membrane.

Answer C

Correct. The ETC components are embedded in membranes because they pump protons across the membranes as electrons move through the chain. This creates a proton gradient (concentration difference) that drives ATP synthesis.

Figure 1. The electron transport chain of cellular respiration. The bold arrows passing through the complexes in the membrane represent the path of electron flow in mitochondria.

Compound X binds to complex IV of the mitochondrial electron transport chain and prevents complex IV from accepting electrons.

Based on Figure 1, which of the following best explains why the cells of an animal exposed to compound X have an increased ratio of NADH to NAD+?

Responses

A

NADH increases because compound X directly prevents synthase from producing the ATP necessary for the oxidation of NADH to NAD+.

B

NADH increases because the binding of compound X to complex IV also prevents the transport of NAD+ out of the mitochondria.

C

NADH cannot be oxidized to NAD+ because complexes I, II, and III cannot accept electrons if electrons cannot be passed to complex IV.

D

NADH cannot be oxidized to NAD+ because H2O cannot bind to the active site of complex IV if this complex cannot accept electrons.

Answer C

Correct. If complex IV is blocked, complexes I, II, and III and will remain reduced and unable to accept any more electrons. NADH will be unable to transfer electrons to complex I and be oxidized to NAD+, resulting in an increase in the ratio of NADH to NAD+ in the cells.

In an experiment, a scientist isolates mitochondria from living cells and suspends them in two different buffered solutions. One solution is maintained at pH 4, while the other solution is maintained at pH 9. The scientist finds that mitochondria in the solution at pH 4 continue to produce ATP but those in the pH 9 solution do not.

The results of the experiment can be used as evidence in support of which of the following scientific claims about mitochondrial activity?

Responses

A

Mitochondria in a cell-free environment are unable to convert thermal energy into ATP.

B

The electron transport chain pumps electrons from the cytosol to the mitochondrial matrix.

C

ATP production in mitochondria requires a hydrogen ion gradient that favors movement of protons into the mitochondrial matrix.

D

ATP synthase molecules change their orientation in relation to the proton gradient across the mitochondrial membrane.

C

ATP production in mitochondria requires a hydrogen ion gradient that favors movement of protons into the mitochondrial matrix.

Which of the following statements is true about the Krebs (citric acid) cycle and the Calvin (light-independent) cycle?

Responses

A

They both result in a net production of ATP and NADH.

B

They both require a net input of ATP.

C

They both result in a release of oxygen.

D

They both take place within the cytoplasmic matrix.

E

They both are carried out by enzymes located within an organelle matrix.

E

They both are carried out by enzymes located within an organelle matrix.

Which of the following best explains why the inner mitochondrial membrane has more embedded proteins of the electron transport chain than the outer mitochondrial membrane?

Responses

A

The inner membrane is more efficient at capturing light than the outer membrane.

B

The inner membrane has a smaller surface area than the outer membrane.

C

The Krebs cycle occurs in the mitochondrial matrix and not the intermembrane space.

D

The outer membrane has a greater surface area for electron transfer.

Answer C

​Correct. Since the Krebs cycle occurs in the mitochondrial matrix, having the electron transport chain in the inner membrane is more efficient as it allows direct access to the NADH and FADH2 produced by the Krebs cycle.​

Which of the following describes a metabolic consequence of a shortage of oxygen in muscle cells?

Responses

A

An increase in blood pH due to the accumulation of lactic acid

B

No ATP production due to the absence of substrate-level phosphorylation

C

A buildup of lactic acid in the muscle tissue due to fermentation

D

A decrease in the oxidation of fatty acids due to a shortage of ATP

C

A buildup of lactic acid in the muscle tissue due to fermentation

The figure above shows an organelle typically found in eukaryotic cells. Which of the following best describes the function of the double membrane system of this organelle?

Responses

A

The outer membrane allows the transport of all molecules into the intermembrane space, while the inner membrane serves as the regulatory boundary.

B

The inner membrane has specialized proteins that create a hydrogen ion concentration gradient between the intermembrane space and the matrix.

C

The outer membrane contains transport proteins that establish a sodium ion concentration gradient used for ATP production, while the inner membrane contains transport proteins that establish a hydrogen ion concentration gradient used for glucose production.

D

The toxins and wastes entering a cell cross the outer membrane and are detoxified by digestive enzymes stored within the intermembrane space.

B

The inner membrane has specialized proteins that create a hydrogen ion concentration gradient between the intermembrane space and the matrix.

In an experiment, researchers compared the growth of two different plants, plant X and plant Y. The researchers maintained the plants under nearly identical conditions and observed that plant X grew faster than plant Y. The researchers also observed that the inner mitochondrial membranes of plant X had more folds than did those of plant Y.

Which of the following conclusions about increasing the number of folds in the inner mitochondrial membrane is best supported by the results of the experiment?

Responses

A

It increases the efficiency of photosynthesis, which results in faster cell growth.

B

It increases the surface area available for ATP production, which results in faster cell growth.

C

It increases the amount of space available for storing cellular wastes, which results in faster cell growth.

D

It increases the rate of protein transport to the plasma membrane, which results in faster cell growth.F

Answer B

Correct. The increased surface area of the folds will contain more ATP synthase, allowing for more efficient use of the chemiosmotic gradient and more efficient production of ATP. The observation that plant X grew faster than plant Y supports this conclusion.

Which of the following best explains how the extensive folding of the inner mitochondrial membrane benefits a eukaryotic cell?

Responses

A

It enlarges the volume of the matrix, which allows for more enzymatic reactions.

B

It increases the area available for proteins involved in energy transfer.

C

It allows for greater area for the diffusion of water into and out of the mitochondria.

D

It provides better insulation for reactions in the matrix from conditions outside the mitochondria.

Answer B

Correct. The extensive folding provides more surface area for proteins involved in energy transfer.

Two nutrient solutions are maintained at the same pH. Actively respiring mitochondria are isolated and placed into each of the two solutions. Oxygen gas is bubbled into one solution. The other solution is depleted of available oxygen. Which of the following best explains why ATP production is greater in the tube with oxygen than in the tube without oxygen?

Responses

A

The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen.

B

Electron transport is reduced in the absence of a plasma membrane.

C

In the absence of oxygen, oxidative phosphorylation produces more ATP than does fermentation.

D

In the presence of oxygen, glycolysis produces more ATP than in the absence of oxygen.

A

The rate of proton pumping across the inner mitochondrial membrane is lower in the sample without oxygen.

The function of which of the following organelles directly requires oxygen?

Responses

A

Ribosome

B

Mitochondrion

C

Nucleus

D

Centriole

E

Golgi apparatus

B

Mitochondrion

Oxygen consumption can be used as a measure of metabolic rate because oxygen is

Responses

A

necessary for ATP synthesis by oxidative phosphorylation

B

necessary to replenish glycogen levels

C

necessary for fermentation to take place

D

required by all living organisms

E

required to break down the ethanol that is produced in muscles

A

necessary for ATP synthesis by oxidative phosphorylation

Some organisms use a weaker terminal electron acceptor than oxygen during cellular respiration. Which of the following best explains why the cells of these organisms might generate less ATP per molecule of glucose than cells that use oxygen as the terminal electron acceptor?

Responses

A

The cells of these organisms remove fewer electrons from glucose than cells that use oxygen.

B

The cells of these organisms create a smaller proton gradient than cells that use oxygen.

C

The cells of these organisms convert pyruvate to lactate more often than cells that use oxygen.

D

The cells of these organisms generate more metabolic heat than cells that use oxygen.

Answer B

Correct. Weaker electron acceptors result in less efficient electron transport chains, which create smaller proton gradients across the membrane. Since ATP synthesis depends on the proton gradient’s strength, less ATP is produced per glucose molecule.

When hydrogen ions are pumped out of the mitochondrial matrix, across the inner mitochondrial membrane, and into the space between the inner and outer membranes, the result is

Responses

A

damage to the mitochondrion

B

the reduction of NAD

C

the restoration of the Na-K balance across the membrane

D

the creation of a proton gradient

E

the lowering of pH in the mitochondrial matrix

D

the creation of a proton gradient

Which metabolic process is common to both aerobic cellular respiration and alcoholic fermentation?

Responses

A

Krebs cycle

B

Glycolysis

C

Electron transport chain

D

Conversion of pyruvic acid to acetyl CoA

E

Production of a proton gradient

B

Glycolysis

Figure 1. The rate of O2 uptake for three species of Saccharomyces yeast at 30 °C and 35 °C

Researchers studied the effect of increased temperature on the rate of respiration of three species of Saccharomyces yeast (Q, R, and S) by measuring the rate of oxygen uptake in each species at 30 °C and at 35 °C (Figure 1).

Based on Figure 1, which of the following statements about the effect of the temperature increase on the respiratory rate of one of the species, Q, R, or S, is most likely true?

Responses

A

The median O2 uptake rate for species S at 35 °C is 0.1 μL*mg^-1 * min^-1 less than it is at 30 °C.

B

The range from minimum to maximum O2 uptake rate for species R at 35 °C is 0.1 μL*mg^-1 * min^-1 more than it is at 30 °C.

C

The median O2 uptake rate for species Q at 35 °C is the same as it is at 30 °C.

D

The range of the O2 uptake rate for species S at 35 °C is the same as it is at 30 °C.

Answer A

Correct. In a box-and-whisker plot, the line inside the box is the median value. For species S at 30 °C, the median O2 uptake rate is 1.4, while at 35 °C, the median uptake rate is 1.3.