Question

Which is the correct order for the process involved in aerobic cellular respiration
A. Krebs cycle, glycolysis, electron transfer chain
B. Glycolysis, Krebs cycle, electron transfer chain
C. Glycolysis, fermentation, electron transfer chain
D. Fermentation, Krebs cycle, electron transfer chain
E. Glycolysis, electron transfer chain, fermentation

Answer 1

The mechanism by which organisms use oxygen to convert food, such as fats and sugars, into chemical energy is aerobic respiration. Anaerobic respiration, by contrast, does not use oxygen.

Complete Answer:
All cells use respiration to transform fuel into energy that can be used for powering cellular processes. The product of respiration is a molecule called adenosine triphosphate (ATP), which utilises the energy stored in its phosphate bonds to power chemical reactions. It is often referred to as the 'currency' of the cell.
Aerobic respiration is much more effective than anaerobic respiration, and generates ATP much more rapidly. This is because oxygen is a great acceptor of electrons for the chemical reactions involved in ATP generation.

The stages involved in aerobic respiration:
1. Glycolysis,
2. A reaction of transition that forms acetyl coenzyme A,
3. The cycle of citric acid (Krebs), an electron transport chain and
4. Chemiosmosis

Four stages:
1. Glycolysis: Aerobic respiration is the aerobic catabolism of carbon dioxide, water and energy nutrients and requires an electron transport mechanism in which the final acceptor of electrons is molecular oxygen.

2. Transition Reaction: Glycolysis is linked to the citric acid (Krebs) cycle by the transformation reaction. The transition reaction transforms the two molecules of the 3-carbon pyruvate from glycolysis (and other pathways) into two molecules of the 2-carbon molecule acetyl coenzyme A (acetyl-CoA) and 2 molecules of carbon dioxide through a mechanism called oxidative decarboxylation.

3. Krebs Cycle: The cycle of citric acid, also known as the cycle of tricarboxylic acid and the cycle of Krebs, completes the oxidation of glucose through the transformation reaction, by taking the pyruvates from glycolysis, and completely breaking them down into $CO_2$, $H_{2}O$, and forming ATP by oxidative phosphorylation.

4. Electron transfer chain and Chemiosmosis: Coupled oxidation-reduction reactions and electron carriers are also part of what is called an electron transport chain during aerobic respiration, a sequence of electron carriers that ultimately transfer electrons to oxygen from NADH and $FADH_2$. NADH and $FADH_2$ diffuse electron carriers carry hydrogen atoms (protons and electrons) from substrates in exergonic catabolic pathways, such as glycolysis and citric acid cycles, to other membrane-embedded electron carriers.

The correct Answer is option (B) Glycolysis, Krebs Cycle, Electron transfer chain.

Note: Aerobic respiration is why we need both oxygen and food, as both are needed to create the ATP that enables our cells to function. We breathe in $O_2$ and we breathe out the same amount of $CO_2$ molecules. It comes from the food that you consume, such as sugar and fat.
This is also why, when doing calorie-burning exercises, you breathe deeper and faster. Your body uses both oxygen and sugar at a higher than average rate and generates more ATP, along with more $CO_2$ waste products, to fuel your cells.