Question
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Sequence of aerobic metabolic breakdown of glucose is
A. Glycolysis-transition-citric acid cycle-electron transport system
B. Transition-glycolysis-electron transport-citric acid cycle
C. Electron transport system-citric acid cycle- transition-glycolysis
D. None of the above

Answer
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Hint: Aerobic respiration is the process of complete oxidation of organic molecules in the presence of molecular oxygen into carbon dioxide and water.

Complete answer:
> Glycolysis is the process in which partial oxidation of glucose occurs to form two molecules of pyruvic acid.

> Complete oxidation of pyruvate occurs and results in the formation of Acetyl coenzyme A. This occurs in the transition phase. It occurs in the mitochondrial matrix .

> Acetyl coenzyme A now enters the cyclic pathway that is the Krebs cycle. In these reactions hydrogen atoms are removed from the acetyl CoA and transferred to the coenzyme for further processing in the electron transport chain.

> The last step is the Electron transport chain. In this process electrons are passed from one carrier to another . This occurs in the inner mitochondrial membrane.

Let's check the given options.
- This the correct sequence as first partial oxidation of glucose occurs then transition and then kreb cycle followed by electron transport chain .Hence this option is correct.
- Glycolysis occurs first and not transition and the kreb cycle occurs first then ETS. So this option is incorrect.
- This sequence is the reverse of the correct sequence . Hence this option is not correct.
- This option is not correct as the first option is true.

> Our correct option is glycolysis then transition followed by kreb cycle and ETS .

Hence, The correct answer is option (A).
That is glycolysis than transition followed by the Kreb cycle and ETS.

Additional information:
Glycolysis is also known as EMP pathway. It is the only process of respiration in anaerobic organisms. Each molecule of glucose produces 2 molecules of pyruvic acid after partial oxidation , at the end of glycolysis. Krebs cycle was named after Hans kerb who first found it in flight muscles of pigeons.

Note: First the pyruvic acid forms from glucose. Then acetyl coenzyme A forms. Then this enzyme enters the kerb's cycle for removal of hydrogen. Now the final step occurs that is the electron transport chain.