AP Biology : Understanding the Electron Transport Chain

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Understanding The Electron Transport Chain

Cellular respiration is dependent on which of the following atoms?

Possible Answers:

Hydrogen

Nitrogen

Oxygen

Carbon

Iron

Correct answer:

Oxygen

Explanation:

In cellular respiration, oxygen is the final electron acceptor. Oxygen accepts the electrons after they have passed through the electron transport chain and ATPase, the enzyme responsible for creating high-energy ATP molecules. Just remember cellular respiration—respiration means breathing, and you cannot breathe without oxygen.

Example Question #2 : Understanding The Electron Transport Chain

Which of the following molecules is the final electron acceptor in the electron transport chain during cellular respiration?

Possible Answers:

O2

CO2

ATP

Glucose

Correct answer:

O2

Explanation:

Oxygen is the final electron acceptor in the electron transport chain, showing the need for aerobic conditions to undergo such a process. ATP is produced as a product of the electron transport chain, while glucose and CO2 play a role in earlier processes of cellular respiration.

Example Question #81 : Cellular Respiration

How many potential ATP can be produced when one molecule of glyceraldehyde-3-phosphate is put through glycolysis?

Possible Answers:

2

3.5

4

4.5

2.5

Correct answer:

3.5

Explanation:

Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate, and one NADH is also produced during that step. NADH enters the electron transport chain, and is therefore worth ATP. Normally, an NADH is worth about 2.5 ATP; however, an NADH produced in glycolysis is only worth 1.5 ATP because it costs 1 ATP to move that NADH from the cytoplasm into the mitochondria. So, in this first step, we have a total of 1.5 ATP.

As the molecule continues on its path to become pyruvate, it will also produce two ATP directly; therefore, we have a net total of 3.5 potential ATP.  

Example Question #1 : Understanding The Electron Transport Chain

Oxygen is necessary for aerobic respiration, because __________.

Possible Answers:

it donates its electrons to the electron transport chain

it establishes the proton gradient

it is necessary in order for ATP synthase to work properly

it is the final electron acceptor in the electron transport chain

Correct answer:

it is the final electron acceptor in the electron transport chain

Explanation:

Oxygen is the final electron acceptor in aerobic respiration. It becomes water upon being reduced by the accepted electrons, which explains why water is one of the products of respiration. Without the presence of oxygen, electrons would remain trapped and bound in the final step of the electron transport chain, preventing further reaction.

NADH and FADH2 are necessary to donate electrons to the electron transport chain.

Example Question #2 : Understanding The Electron Transport Chain

What happens to the electron transport chain when oxygen is not available?

Possible Answers:

Oxidative phosphorylation can continue without any noticeable impact

Oxidative phosphorylation will produce oxygen from available carbon dioxide

Oxidative phosphorylation will utilize carbon dioxide instead of oxygen

Oxidative phosphorylation utilizes alternative fuel sources, such as fats

Oxidative phosphorylation ceases and the cell reverts to fermentation after glycolysis

Correct answer:

Oxidative phosphorylation ceases and the cell reverts to fermentation after glycolysis

Explanation:

Oxygen is the final electron acceptor in the electron transport chain, which allows for oxidative phosphorylation. Without oxygen, the electrons will be backed up, eventually causing the electron transport chain to halt. This will cause the products of glycolysis to go through fermentation instead of going to the citric acid cycle. Without oxygen, oxidative phosphorylation (the electron transport chain) is impossible, but substrate-level phosphorylation (glycolysis) continues.

Example Question #3 : Understanding The Electron Transport Chain

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

Possible Answers:

Glycolysis

Krebs cycle

Substrate-level phosphorylation

Oxidative phosphorylation

Citric acid cycle

Correct answer:

Oxidative phosphorylation

Explanation:

Cellular respiration typically follows three steps, under aerobic conditions. Glycolysis generates NADH and converts glucose to pyruvate, while producing small amounts of ATP through substrate-level phosphorylation. The citric acids cycle, or Krebs cycle, uses pyruvate to generate more NADH and FADH2. These NADH and FADH2 molecules donate electrons to the electron transport chain, which are used to pump protons into the intermembrane space of the mitochondrion. The protons in the intermembrane space then flow through ATP synthase to generate large amounts of ATP via oxidative phosphorylation.

Example Question #424 : Ap Biology

Why is oxygen essential for the electron transport chain?

Possible Answers:

It serves as the primary electron donor

It is part of the chemiosmotic gradient

It serves as the terminal electron acceptor

It is essential for transporting pyruvate into the mitochondria

Correct answer:

It serves as the terminal electron acceptor

Explanation:

Oxygen serves as the terminal electron acceptor for the electron transport chain. Electrons are donated by NADH molecules and passed through several different proteins to generate the proton gradient in the intermembrane space. Upon reaching the final protein, the electron is bonded to an oxygen molecule to create water. Without oxygen, there would be nowhere for the electrons to go after being pumped through the electron transport chain, and aerobic cellular respiration would be impossible.

Example Question #4 : Understanding The Electron Transport Chain

Which of the following processes requires an electron acceptor?

Possible Answers:

Glycolysis requires a nitrogen electron acceptor

The electron transport chain requires a nitrogen electron acceptor

The citric acid cycle requires an oxygen electron acceptor

The electron transport chain requires an oxygen electron acceptor

Correct answer:

The electron transport chain requires an oxygen electron acceptor

Explanation:

Oxygen acts as the terminal electron acceptor in the electron transport chain (ETC). This accounts for the reason as to why, when cells are starved of oxygen, the ETC "backs up" and the cell will divert to using anaerobic respiration, such as fermentation. At the end of the electron transport chain, the electron and a proton are passed to an oxygen molecule to produce water.

The citric acid cycle depends on oxygen in an indirect sense. The main purpose of the cycle is to produce electron donors for the electron transport chain. If the chain is not functional (due to lack of oxygen), the citric acid cycle also stops functioning. Glycolysis is not dependent on oxygen, and can function in anaerobic environments.

Example Question #5 : Understanding The Electron Transport Chain

The chemical compound 2,4-dinitrophenol can disrupt the process of oxidative phosphorylation in the mitchondrial electron transport chain by causing which effect?

Possible Answers:

Binding to ubiquinone

Oxidative inhibition

Binding to nucleotide carriers

Removing the F0 subunit from the ATP synthase complex

Dispersion of the proton gradient

Correct answer:

Dispersion of the proton gradient

Explanation:

In ATP synthesis, the proton gradient is an interconvertible form of energy in electron transport. 2,4-dinitrophenol is an inhibitor of ATP production in cells with mitochondria. Its mechanism of action involves carrying protons across the mitochondrial membrane, which leads to the consumption of energy without ATP production.

The other answer choices are not directly related to the generation of the proton gradient.

Example Question #6 : Understanding The Electron Transport Chain

If cellular respiration were 100% efficient, the process should produce around eighty ATP, however, the actual yield is around thirty ATP. What happens to the rest of the chemical energy in glucose?

Possible Answers:

It is stored as fat

It is released as carbon dioxide and water

It is converted to starch

It is used to make water from hydrogen ions and oxygen

It is converted to heat

Correct answer:

It is converted to heat

Explanation:

Cellular respiration is only about 38% efficient, with the rest of the energy in glucose lost as heat.

Water and carbon dioxide are not used to store energy. Fats can be synthesized from acetyl CoA and glycerol, but are not generally created in large quantities during cellular respiration. Starches are generally used for energy storage in plants, but can be synthesized from glucose; however, starches are not a standard product of cellular respiration.

Most of the reactions in cellular respiration are exothermic, in order to support spontaneous reaction. The result is release of heat energy with most steps.

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