Biology

Cellular Respiration and Enzymes

1,721 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice

Which molecule enters the Krebs Cycle?

  1. Glucose

  2. Pyruvate

  3. Acetyl-CoA

  4. Citrate
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Acetyl-CoA, derived from the breakdown of carbohydrates, fats, and proteins, is the molecule that enters the Krebs Cycle.

Multiple choice

What is the first reaction of the Krebs Cycle?

  1. Condensation of acetyl-CoA with oxaloacetate to form citrate

  2. Isomerization of citrate to isocitrate

  3. Oxidation of isocitrate to α-ketoglutarate

  4. Decarboxylation of α-ketoglutarate to succinyl-CoA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The first reaction of the Krebs Cycle is the condensation of acetyl-CoA with oxaloacetate to form citrate, catalyzed by the enzyme citrate synthase.

Multiple choice

Which reaction of the Krebs Cycle produces the most ATP?

  1. Conversion of isocitrate to α-ketoglutarate

  2. Decarboxylation of α-ketoglutarate to succinyl-CoA

  3. Conversion of succinyl-CoA to succinate

  4. Oxidation of succinate to fumarate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The decarboxylation of α-ketoglutarate to succinyl-CoA, catalyzed by the enzyme α-ketoglutarate dehydrogenase, is the reaction that produces the most ATP in the Krebs Cycle.

Multiple choice

What is the final product of the Krebs Cycle?

  1. Oxaloacetate

  2. Malate

  3. Fumarate

  4. Succinate
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The final product of the Krebs Cycle is oxaloacetate, which is regenerated to start the cycle again.

Multiple choice

How many molecules of ATP are produced per glucose molecule through the Krebs Cycle?

  1. 2

  2. 4

  3. 6

  4. 8
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Krebs Cycle directly produces 2 molecules of ATP per glucose molecule.

Multiple choice

What is the role of NADH and FADH2 in the Krebs Cycle?

  1. They are electron carriers that transfer electrons to the electron transport chain

  2. They are used to generate ATP through oxidative phosphorylation

  3. They are involved in the decarboxylation reactions of the Krebs Cycle

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

NADH and FADH2 are electron carriers that transfer electrons to the electron transport chain, where ATP is generated through oxidative phosphorylation. They are also involved in the decarboxylation reactions of the Krebs Cycle.

Multiple choice

Which enzyme catalyzes the conversion of isocitrate to α-ketoglutarate?

  1. Citrate synthase

  2. Aconitase

  3. Isocitrate dehydrogenase

  4. α-Ketoglutarate dehydrogenase
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The conversion of isocitrate to α-ketoglutarate is catalyzed by the enzyme isocitrate dehydrogenase.

Multiple choice

What is the name of the enzyme that catalyzes the decarboxylation of α-ketoglutarate to succinyl-CoA?

  1. Citrate synthase

  2. Aconitase

  3. Isocitrate dehydrogenase

  4. α-Ketoglutarate dehydrogenase
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The decarboxylation of α-ketoglutarate to succinyl-CoA is catalyzed by the enzyme α-ketoglutarate dehydrogenase.

Multiple choice

Which reaction of the Krebs Cycle involves the transfer of a high-energy phosphate group to GDP to form GTP?

  1. Conversion of isocitrate to α-ketoglutarate

  2. Decarboxylation of α-ketoglutarate to succinyl-CoA

  3. Conversion of succinyl-CoA to succinate

  4. Oxidation of succinate to fumarate
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The conversion of succinyl-CoA to succinate, catalyzed by the enzyme succinyl-CoA synthetase, involves the transfer of a high-energy phosphate group to GDP to form GTP.

Multiple choice

What is the name of the enzyme that catalyzes the oxidation of succinate to fumarate?

  1. Succinate dehydrogenase

  2. Fumarase

  3. Malate dehydrogenase

  4. Citrate synthase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The oxidation of succinate to fumarate is catalyzed by the enzyme succinate dehydrogenase.

Multiple choice

Which reaction of the Krebs Cycle involves the addition of water to fumarate to form malate?

  1. Conversion of isocitrate to α-ketoglutarate

  2. Decarboxylation of α-ketoglutarate to succinyl-CoA

  3. Conversion of succinyl-CoA to succinate

  4. Oxidation of succinate to fumarate
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The addition of water to fumarate to form malate is catalyzed by the enzyme fumarase.

Multiple choice

What is the name of the enzyme that catalyzes the oxidation of malate to oxaloacetate?

  1. Succinate dehydrogenase

  2. Fumarase

  3. Malate dehydrogenase

  4. Citrate synthase
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The oxidation of malate to oxaloacetate is catalyzed by the enzyme malate dehydrogenase.

Multiple choice

Which of the following is the first stage of cellular respiration?

  1. Glycolysis

  2. Krebs cycle

  3. Electron transport chain

  4. Oxidative phosphorylation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Glycolysis is the first stage of cellular respiration. It is a series of ten enzymatic reactions that occur in the cytoplasm of cells and result in the breakdown of glucose into two molecules of pyruvate.

Multiple choice

What is the name of the series of chemical reactions that occur in the mitochondria of cells and result in the production of ATP?

  1. Glycolysis

  2. Krebs cycle

  3. Electron transport chain

  4. Oxidative phosphorylation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Oxidative phosphorylation is the series of chemical reactions that occur in the mitochondria of cells and result in the production of ATP. This process involves the transfer of electrons through a series of protein complexes, which generates a proton gradient that is used to drive the synthesis of ATP.

Multiple choice

Which of the following is the final electron acceptor in the electron transport chain?

  1. Oxygen

  2. NADH

  3. FADH2

  4. Cytochrome c
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Oxygen is the final electron acceptor in the electron transport chain. It accepts electrons from cytochrome c oxidase and combines with them to form water.