Question

Enumerate the assumptions that we undertake in making the respiratory balance sheet. Are these assumptions valid for a living system? Compare fermentation and aerobic respiration in this context.

Answer 1

The respiratory balance sheet is calculated based on the following assumptions:

Respiration is a sequential process that follows an orderly pattern.

Once NADH has been synthesized through glycolysis, it is oxidatively phosphorylated in the mitochondria.

No intermediate in the pathway can be used to synthesize a compound.

Oxidation of glucose is the only process occurring. Neither intermediate substrates nor intermediate products are utilized.

These assumptions, however, do not apply to a living system. Because pathways operate simultaneously, they are not always sequential. Adenosine triphosphate and ATP are used when needed. Glucose may not be the only fuel available. Although this calculation has practical limitations, it is nonetheless very useful.

Fermentation	Aerobic respiration
(i) Partial breakdown of glucose happens during this process into ethanol.	(i) Complete breakdown of glucose takes place into carbon dioxide.
(ii) There is a net gain of only two ATP molecules.	(ii) There can be a net gain of 36 molecules of ATP.
(iii) Oxidation of NADH to NAD+ is slow.	(iii) Oxidation of NADH to NAD+ is very fast.