Question

What is the correct order of the stages of cellular respiration?
A) Krebs cycle electron transport - chain glycolysis
B) Electron transport chain - Krebs cycle - glycolysis
C) Glycolysis - Krebs cycle - electron transport chain
D) Glycolysis - electron transport chain - Krebs cycle

Answer 1

Hint: Cellular respiration is the mechanism of breakdown of food materials within the cells to release energy, and the trapping of this energy for ATP synthesis cellular respiration is of two types – Aerobic respiration and anaerobic respiration.

Complete Answer:
(i) For cellular respiration, the common substrate is glucose.
(ii) Glucose is firstly commented into 2 molecules of pyruvate by glycolysis pathway. Glycolysis occurs in cytoplasm.
(iii) The pyruvate formed is converted into Acetyl (\[CoA\] by oxidative decarboxylation process.
(iv) This Acetyl \[CoA\] then enters kreb’s cycle. In kreb’s cycle, Acetyl \[CoA\] is oxidized to form \[C{O_2},\]\[\;ATP,{\text{ }}NADH,{\text{ }}FAD{H_2}.\] Krebs cycle takes place in the mitochondrial Matrix. Kreb’s cycle is also called Citric acid cycle.
(vi)\[NADH\] and \[FAD{H_2}\] are used as the reducing power in the Electron Transport chain for ATP synthesis. ETC occurs in inner
mitochondrial membrane. Therefore, the correct order for the stages involved in cellular respiration is glycolysis, then Kreb’s
Cycle and electron transport chain.

The correct option is C.

Note: Glycolysis was discovered by three German scientists Embden, Meyerhof and Parnas, also called EMP Pathway.
(i) Kreb cycle (citric acid cycle) was proposed by Hans Adolf Krebs in 1937 based on the studies of oxygen consumption in
Pigeon breast muscles.
(ii) In Electron transport chain, the inner mitochondrial membrane has groups of several photons \[\left( {{H^ + }} \right)\] and electrons \[\left( {{e^ - }} \right)\] acceptors. These groups are arranged in a specific series called Electron Transport Chain (ETC) or Electron Transport System
(ETS).
(iii) Net gain of \[36{\text{ }}ATP\] molecules during aerobic respiration of one molecule of glucose.