Respiratory Balance Sheet – Class 11 | Chapter – 14 | Biology Short Notes Series PDF

Respiratory Balance Sheet: The respiratory balance sheet deals with the gain and loss of energy in the form of an energy currency called ATP. The balance sheet can be drawn only theoretically. There are certain assumptions considered to draw a balance sheet. It is assumed that the process of respiration is a sequential and orderly process.

Assumptions of Respiratory Balance Sheet

Theoretical calculation of ATP generation is based upon certain assumptions, which are listed below:

1. The process of respiration is sequential and orderly. The pathway involves steps glycolysis–> TCA cycle –>ETS pathway.
2. Every NADH molecule produced during glycolysis is transferred into the mitochondria for oxidative phosphorylation and ATP generation.
3. Respiration is an isolated pathway, and intermediates formed along the pathway are not utilised to synthesise any other compound.
4. Glucose is the only respiratory substrate being used for ATP generation. Other substrates like protein and fat do not enter the pathway at any stages.

Respiratory Balance Sheet

Aerobic Respiration

C₆H₁₂O₆ + 6O₂   → 6CO₂ + 6H₂O + 673Kcal

Aerobic respiration involves the complete combustion of glucose. Typically, during the electron transport system in aerobic respiration, oxidation of each NADH molecule produces three ATP and oxidation of each FADH₂ molecule produces two ATP molecules. The numbers of ATP produced vary in prokaryotes and eukaryotes.

1NADH→3ATP1NADH→3ATP
1FADH2→2ATP1FADH2→2ATP

Phase	Molecular change	Cost per glucose molecule	Gain per glucose molecule
Glycolysis	Conversion of glucose(6C) to 2 pyruvates (3C)	2ATP	4 ATP 2 NADH
Oxidation of pyruvates	Conversion of pyruvates(3C) to acetyl group (2C)	None	2 NADH
Krebs cycle	Conversion of citric acid(6C) formed by the combination of an acetyl group and oxaloacetate to oxaloacetate(4C)	None	2 ATP 6 NADH 2 FADH2
Electron transport	oxidation of NADH and FADH2 to build ATP and water molecules	2ATP	34 ATP

Pathway	NADH (3 ATP)	FADH2 (2 ATP)	ATP	Total
EMP pathway/ glycolysis	2 x 3 = 6	—	Produced- 4 Utilised- 2 Net gain- 2	8
2 x Pyruvate oxidation to acetyl CoA	2 x 3 = 6	–	–	6
Krebs cycle	6 x 3 = 18	2 x 2 = 4	2	24
Total	10 x 3 = 30	2 x 2 = 4	4	38

The net gain of ATP is 36 in most eukaryotes, while it is 38 in prokaryotes.

Significance of Respiratory Balance Sheet

Theoretical calculation suggests a net gain of 38 ATP during the complete oxidation of a glucose molecule. Although the practical calculation is not possible, we do the calculation for the following reasons:

1. To estimate the net gain of ATP
2. To understand the efficiency of the living system in extraction and storing energy

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By Team Learning Mantras