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Biology Question 91 – NEET-UG 2025

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The complex II of mitochondrial electron transport chain is also known as

Recall the different protein complexes involved in the mitochondrial electron transport chain (ETC) and their primary functions.

Step 1: Recall the Mitochondrial Electron Transport Chain Complexes✦ Active

The mitochondrial electron transport chain (ETC) consists of four major protein complexes (Complex I, II, III, and IV) and ATP synthase (Complex V). Each complex has a specific name and function in the process of oxidative phosphorylation.

💡 Teacher's Secret Hint

Remember that the ETC is crucial for generating ATP through oxidative phosphorylation.

Step 2: Identify Complex II○ Expand

Complex II of the mitochondrial electron transport chain is also known as succinate dehydrogenase. This enzyme is unique because it is the only complex of the ETC that is directly involved in the citric acid cycle (Krebs cycle), where it catalyzes the oxidation of succinate to fumarate, reducing FAD to FADH2.

💡 Teacher's Secret Hint

Don't confuse Complex II with other complexes like NADH dehydrogenase (Complex I) or Cytochrome c oxidase (Complex IV).

Step 3: Evaluate the Options○ Expand

Let's match the given options to their respective complexes in the electron transport chain:

(1) Cytochrome bc1 is Complex III.

(2) Succinate dehydrogenase is Complex II.

(3) Cytochrome c oxidase is Complex IV.

(4) NADH dehydrogenase is Complex I.

Therefore, option (2) is the correct answer.

💡 Teacher's Secret Hint

Knowing the alternative names for each complex is key for such questions.

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