Biology: Citric Acid Cycle Quiz
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Questions and Answers

Which molecule is oxidized during the citric acid cycle?

  • Oxaloacetate
  • Acetyl CoA (correct)
  • NAD+
  • FAD

What is produced from 2 Acetyl CoA during the citric acid cycle?

  • 2 NADH
  • 4 CO2 (correct)
  • 6 OAA
  • 2 ATP (correct)

Which of the following statements is true regarding NADH and FADH2?

  • They serve as electron carriers. (correct)
  • They are both oxidized forms of NAD+ and FAD.
  • They do not have potential energy.
  • They are produced during glycolysis.

What is the primary location of the citric acid cycle within the cell?

<p>Mitochondrial matrix (D)</p> Signup and view all the answers

Which molecules are reduced during the citric acid cycle?

<p>6 NAD+ and 2 FAD (A)</p> Signup and view all the answers

What is the process called when protons move back across the selectively permeable membrane from high concentration to low concentration?

<p>Chemiosmosis (A)</p> Signup and view all the answers

Which sequence correctly represents the flow of electrons during aerobic cellular respiration?

<p>Glucose → Electron carriers → Electron transport chain → Water (A)</p> Signup and view all the answers

What is the net ATP production from cellular respiration, considering the given values for NADH and FADH2?

<p>28-32 (A)</p> Signup and view all the answers

Which type of fermentation occurs in mammals in the absence of oxygen?

<p>Lactic acid fermentation (A)</p> Signup and view all the answers

During fermentation, what is the key purpose of regenerating NAD+?

<p>To allow glycolysis to continue (D)</p> Signup and view all the answers

What role does NAD+ play in redox reactions?

<p>It serves as an oxidizing agent by accepting electrons. (D)</p> Signup and view all the answers

What is oxidation defined as in the context of redox reactions?

<p>Loss of electrons. (A)</p> Signup and view all the answers

What does an oxidizing agent do during a redox reaction?

<p>It accepts electrons from another compound. (A)</p> Signup and view all the answers

Which of the following correctly describes the flow of energy through living systems?

<p>Carbohydrate → respiration → ATP → heat. (A)</p> Signup and view all the answers

What defines an energy shell in an atom?

<p>A distance from the nucleus where electrons have varying potentials. (D)</p> Signup and view all the answers

Which statement about reduction in a redox reaction is accurate?

<p>It always occurs simultaneously with oxidation. (C)</p> Signup and view all the answers

How is energy from the sun ultimately utilized in living organisms?

<p>It transforms into carbohydrates through photosynthesis. (C)</p> Signup and view all the answers

What change occurs to NAD+ when it accepts an electron?

<p>It transforms into NADH. (B)</p> Signup and view all the answers

Which process generates the most ATP per glucose molecule?

<p>Aerobic respiration (A)</p> Signup and view all the answers

What is the final product of alcoholic fermentation?

<p>Ethanol (D)</p> Signup and view all the answers

Which pathway occurs in the absence of oxygen?

<p>Fermentation (A)</p> Signup and view all the answers

In which process is NAD+ used as an input during glycolysis?

<p>Fermentation (B)</p> Signup and view all the answers

Which of the following does NOT require oxygen as an input?

<p>Fermentation (A)</p> Signup and view all the answers

What is the primary purpose of fermentation?

<p>To regenerate NAD+ (A)</p> Signup and view all the answers

Which molecule accepts electrons in the initial glycolysis process?

<p>NAD+ (D)</p> Signup and view all the answers

Which pathway produces lactate as a final product?

<p>Lactic acid fermentation (D)</p> Signup and view all the answers

Which example represents the reduced forms of the two major electron carriers?

<p>NADH and FADH2 (B)</p> Signup and view all the answers

Why do some marathon runners attempt to 'carbo load' before a big race?

<p>The bonds in carbohydrates have high potential energy. (B)</p> Signup and view all the answers

Which of the following summarizes the net final products of glycolysis?

<p>Two molecules of pyruvate, two molecules of ATP, and two molecules of NADH (D)</p> Signup and view all the answers

Tracing the metabolism of one glucose molecule, how many carbon atoms are available for further oxidation at the completion of the pyruvate oxidation stage?

<p>2 (C)</p> Signup and view all the answers

Once processed through the citric acid cycle, the acetyl-CoA molecules from a single glucose molecule produce:

<p>2 ATP, 6 NADH, 4 CO2, and 2 FADH2 (D)</p> Signup and view all the answers

What happens to the pH in the intermembrane space as hydrogen ions are moved into it?

<p>It becomes more acidic. (B)</p> Signup and view all the answers

Which of the following creates a proton gradient in cellular respiration?

<p>The electron transport chain. (A)</p> Signup and view all the answers

How do protons move through ATP synthase?

<p>Facilitated diffusion. (C)</p> Signup and view all the answers

What occurs when oxygen combines with protons and electrons?

<p>It is reduced. (B)</p> Signup and view all the answers

What happens to the pH of the mitochondrial matrix in the absence of oxygen?

<p>It would go down. (D)</p> Signup and view all the answers

What could be added to restore citric acid cycle activity in the absence of oxygen?

<p>NAD+ or FAD. (B)</p> Signup and view all the answers

Which effect might be expected from the presence of oligomycin, an antibiotic that blocks ATP synthase?

<p>Lower pH in the intermembrane space. (A), A buildup of protons in the mitochondrial matrix. (D)</p> Signup and view all the answers

Which molecule carries the smallest amount of potential energy derived from glucose during cellular respiration?

<p>ATP. (A)</p> Signup and view all the answers

Flashcards

Oxidation

The loss of electron(s) in a chemical reaction.

Reduction

The gain of electron(s) in a chemical reaction.

Redox Reaction

A chemical reaction involving both oxidation and reduction.

Oxidizing agent

A substance that oxidizes another substance by accepting electrons.

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Reducing agent

A substance that reduces another substance by donating electrons.

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NAD+

Oxidized form of the coenzyme NAD.

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NADH

Reduced form of coenzyme NAD, after gaining an electron.

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Electron Carrier

A molecule that accepts and donates electrons in redox reactions.

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Pyruvate

A three-carbon molecule that is a product of glycolysis.

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Citric Acid Cycle

Completes the breakdown of glucose; occurs in the mitochondrial matrix; produces NADH and FADH2.

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Acetyl CoA

A two-carbon molecule that enters the citric acid cycle.

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Oxidation/Reduction

Oxidation is the loss of electrons in a molecule and reduction is the gain. Electrons carry potential energy.

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NADH higher potential energy

NADH, produced during oxidation, has more potential energy than NAD+.

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Aerobic Cellular Respiration

The process of breaking down glucose in the presence of oxygen to produce ATP.

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Chemiosmosis

The movement of protons across a membrane to generate ATP.

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Electron Carriers (e.g., NADH, FADH2)

Molecules that carry electrons during cellular respiration.

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Fermentation

A process that occurs in the absence of oxygen to regenerate NAD+ for glycolysis.

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ATP Production (Cellular Respiration)

The net production of ATP molecules by cellular respiration is approximately 28-32.

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Alcohol Fermentation

A type of anaerobic respiration where glucose is converted to ethanol, releasing NAD+.

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Lactic Acid Fermentation

A type of anaerobic respiration where glucose is converted to lactate, regenerating NAD+.

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Fermentation and Aerobic Respiration Similarities

Both use glycolysis, and regenerate NAD+ in the absence of oxygen, by converting pyruvate into a different end product.

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Fermentation vs. Respiration ATP

Fermentation produces 2 ATP per glucose, while aerobic cellular respiration produces 32-38 ATP per glucose.

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Anaerobic pathways

Biochemical pathways that do not require oxygen.

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Glycolysis input

A key input to Glycolysis is NAD+ It is then converted into NADH.

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Fermentation output

Fermentation produces NAD+ by converting pyruvate into ethanol or lactate.

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Oxygen-requiring pathways

Biochemical pathways that require oxygen for the final steps of respiration.

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Reduced Electron Carriers

NADH and FADH2, the reduced forms of electron carriers, carry high-energy electrons to the electron transport chain.

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Carbo Loading (Marathon)

Eating high-carbohydrate foods before a race to store glycogen for energy.

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Glycolysis Final Products

Two pyruvate, two ATP, and two NADH molecules.

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Pyruvate Oxidation Carbon Atoms

Two carbon atoms are available for further oxidation after pyruvate oxidation.

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Citric Acid Cycle Output (Per Glucose)

Two ATP, six NADH, four CO2, and two FADH2 are generated per glucose molecule.

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pH change in intermembrane space

The pH in the intermembrane space of mitochondria becomes more acidic as hydrogen ions are pumped into it during the electron transport chain.

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Electron Transport Chain (ETC) energy type

The ETC creates a proton gradient, storing potential energy.

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Proton movement in ATP synthase

Protons move through ATP synthase by facilitated diffusion.

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Oxygen's role in ETC

Oxygen combines with protons and electrons to form water; it becomes reduced.The reduction of oxygen in the ETC is crucial for maintaining the electron flow and preventing the build-up of electrons in the system.

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Citric Acid Cycle in absence of Oxygen

In the absence of oxygen, the citric acid cycle and pyruvate oxidation stop.

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Matrix pH in absence of O2

Without oxygen, increasing the pH of the matrix of the mitochondria is expected as electrons are not drained resulting in build-up within the matrix.

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Proton gradient and ATP synthesis

Conditions that weaken the proton gradient slow down the production of ATP by ATP synthase.

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Restoration of Citric Acid Cycle without oxygen

Adding glucose, acetyl-CoA, or NAD+/FAD to the system might restore citric acid cycle and pyruvate oxidation activity when oxygen is depleted.

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