Question 1

For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle (see Figure 7.1)?

Accepted Answer

In the citric acid cycle, each mole of glucose is fully oxidized, leading to the release of 6 moles of CO2. However, the citric acid cycle only oxidizes half a glucose molecule, leading to the release of 3 moles of CO2. Since one mole of glucose leads to the oxidation of two molecules of pyruvate, which in turn enter the citric acid cycle, the total number of moles of CO2 released in the citric acid cycle is 6 (3 moles of CO2 per pyruvate molecule, times 2 pyruvate molecules per glucose molecule). Therefore, the correct answer is B, 4 moles of CO2 per mole of glucose oxidized.

Question 2

Starting with citrate, which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see Figure 7.1)?

Accepted Answer

Each acetyl CoA entering the citric acid cycle results in the production of 1 ATP, 2 CO2, 3 NADH, and 1 FADH2. Therefore, three acetyl CoA molecules entering the cycle would result in the production of 3 ATP, 6 CO2, 9 NADH, and 3 FADH2. Option D is the only one that matches this combination. Option A is incorrect because it only includes 1 ATP, while option B includes too many FADH2 molecules. Option C is incorrect because it includes too many ATP molecules, and option E is incorrect because it includes too few CO2 molecules.

Question 3

One function of both alcohol fermentation and lactic acid fermentation is to

Accepted Answer

Both alcohol fermentation and lactic acid fermentation oxidize NADH to NAD+ to regenerate NAD+ for glycolysis to continue producing ATP anaerobically.

Question 4

What is the purpose of beta oxidation in respiration?

Accepted Answer

Beta oxidation is the breakdown of fatty acids into acetyl-CoA, which can enter the citric acid cycle and generate ATP through oxidative phosphorylation.

Question 5

What happens at the end of the chain in Figure 7.2?

Accepted Answer

Four electrons combine with a molecule of oxygen and 4 protons.

Question 6

You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body?

Accepted Answer

When the body loses fat, it is primarily broken down into carbon dioxide (CO2) and water (H2O), which are then eliminated through breathing, sweating, and urination. This process is known as oxidation and involves the metabolism of fats by the body's cells to produce energy. Therefore, option A is the best choice.

Question 7

Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle. Which intermediate would supply the carbon skeleton for synthesis of a five-carbon amino acid (see Figure 7.1)?

Accepted Answer

α-ketoglutarate is a five-carbon intermediate in the citric acid cycle and would supply the carbon skeleton for the synthesis of a five-carbon amino acid.

Question 8

Figure 7.1
The citric acid cycle.
-Starting with one molecule of isocitrate and ending with fumarate, how many ATP molecules can be made through substrate-level phosphorylation (see Figure 7.1)?

Accepted Answer

The answer of  Figure 7.1
The citric acid cycle.
-Starting with...

Question 9

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

Accepted Answer

Glycolysis does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms. These characteristics suggest that it evolved early in the history of life and is present in both prokaryotes and eukaryotes.

Question 10

An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism

Accepted Answer

The fact that the organism can thrive both in the presence and absence of oxygen suggests that it is a facultative anaerobe. The increase in sugar consumption when oxygen is removed suggests that the organism is switching to an alternative energy source, likely fermentation, which does not result in much weight gain.

Question 11

Which of the following most accurately describes what is happening along the electron transport chain in Figure 7.2?

Accepted Answer

Along the electron transport chain, each electron carrier alternates between being reduced (accepting electrons) and being oxidized (donating electrons), creating a flow of electrons through the chain. This flow of electrons is what drives the pumping of protons across the membrane, creating a proton gradient and allowing chemiosmosis to occur, ultimately generating ATP. The energy of the electrons does not increase at each step; rather, molecules in the chain give up some of their potential energy. Therefore, the best choice is B.

Question 12

If pyruvate oxidation is blocked, what will happen to the levels of oxaloacetate and citric acid in the citric acid cycle shown in Figure 7.1?

Accepted Answer

In pyruvate oxidation, pyruvate is converted into acetyl-CoA, which is then used to combine with oxaloacetate to form citric acid. If pyruvate oxidation is blocked, then there will be no acetyl-CoA to combine with oxaloacetate, leading to a buildup of oxaloacetate and a decrease in citric acid levels. Therefore, the best choice is C, where oxaloacetate will accumulate and citric acid will decrease.

Question 13

Figure 7.2
-Figure 7.2 shows the electron transport chain. Which of the following is the combination of substances that is initially added to the chain?

Accepted Answer

NADH and FADH2 are initially added to the electron transport chain, and oxygen is the final electron acceptor.

Question 14

Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle?

Accepted Answer

The catabolic products of fatty acid breakdown, specifically acetyl CoA, enter into the citric acid cycle by combining with oxaloacetate to form citrate.

Question 15

When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells?

Accepted Answer

Lactate produced in skeletal muscle cells is transported to the liver where it is converted back to pyruvate through a process called gluconeogenesis, which can then be used for energy production. This process helps to prevent a buildup of lactate in the muscle, which can lead to muscle fatigue and cramping.

Question 16

During intense exercise, as skeletal muscle cells switch to fermentation, the human body will increase its catabolism of

Accepted Answer

As skeletal muscle cells switch to fermentation, the human body will increase its catabolism of carbohydrates only. This is because fermentation involves the breakdown of glucose to produce ATP without the use of oxygen, and carbohydrates are the primary source of glucose in the body. Fats and proteins can also be metabolized for energy, but they are not preferred during intense exercise when quick energy is needed.

Question 17

Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth?

Accepted Answer

The fact that glycolysis is widespread and present in all three domains of life (Bacteria, Archaea, and Eukarya) suggest that it is an ancient metabolic pathway that predates the divergence of these domains.

Question 18

Which of the protein complexes labeled with Roman numerals in Figure 7.2 will transfer electrons to O2?

Accepted Answer

Complex IV, also known as cytochrome c oxidase, transfers electrons to O2 by catalyzing the reduction of O2 to H2O. None of the other complexes transfer electrons directly to O2.

Question 19

A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?

Accepted Answer

Yeast cells rely on anaerobic fermentation to generate ATP under oxygen-deprived conditions. Without the ability to convert pyruvate to ethanol, the mutant yeast will be unable to carry out anaerobic fermentation and generate ATP. Therefore, the mutant yeast will be unable to grow anaerobically.

Question 20

For each molecule of glucose that is metabolized by glycolysis and the citric acid cycle (see Figure 7.1), what is the total number of NADH + FADH2 molecules produced?

Accepted Answer

Glycolysis produces 2 NADH molecules, and the citric acid cycle produces 6 NADH and 2 FADH2 molecules. Therefore, the total number of NADH + FADH2 molecules produced is 2 + 6 + 2 = 10.

Quiz 7: Cellular Respiration and Fermentation

For each mole of glucose (C6H12O6) oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle (see Figure 7.1) ?

Starting with citrate, which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see Figure 7.1) ?