Question

How much of the energy released during aerobic respiration is approximately conserved in the form of ATP ?
a. $20\% $
b. $40\% $
c. $60\% $
d. $100\% $

Answer 1

Hint: We all need energy to do work and we breathe to live. Respiration is the gaseous exchange where the $C - C$ bonds break through oxidation in the cells. This process yields energy and the compounds that are oxidised are the respiratory substrates. Respiration is basically aerobic and anaerobic. Aerobic respiration takes place in the mitochondria which is the ‘powerhouse’ of the cell. The final product of glycolysis, pyruvate is transported from the cytoplasm into the mitochondria.

Complete answer:
Aerobic respiration uses oxygen and there are a series of crucial events yielding a certain amount of energy which is not $20\% $ as it is very low for such a high energy yielding complex process. Fermentation is an anaerobic process where the glucose oxidation is incomplete and pyruvate is converted to $CO_2$ and ethanol. In animal cells, like muscles during exercise, when there is an inadequate supply of oxygen then pyruvic acid is reduced to lactic acid by lactate dehydrogenase.

Aerobic respiration is the process of complete oxidation of organic substances in the presence of oxygen and releasing $CO_2$ , water and a large amount of energy present in the substrate. The equation can be stated as,
 $glucose + oxygen \to carbon dioxide + water + energy$.
On completion of one oxidation the amount of energy yielded is $38 ATP$ molecules which is approx $40\% $ release of energy during aerobic respiration stored in the form of ATP.

As from the equation and the statement above the other two options are not the amount of ATP or energy released during aerobic respiration. The complete oxidation of pyruvate by the stepwise removal of all the hydrogen atoms, leaving three molecules of carbon dioxide. The passing on of the electrons removed as part of the hydrogen atoms to molecular oxygen with simultaneous synthesis of ATP .

Hence, The correct answer is option (B).

Note: It is very interesting to note that the complete oxidation of pyruvate takes place in the mitochondrial matrix whereas the electron passing with ATP synthesis takes place in the inner membrane of mitochondria. Aerobic respiration is most common in higher organisms. The respiratory pathway is an amphibolic pathway as it involves both anabolism and catabolism.