Question

When malic acid is a respiratory substrate, what is the amount of CO₂ released?

Answer 1

Respiratory substrate: Any biomolecule or compound that undergoes oxidation during respiration to liberate energy is termed a respiratory substrate.

1. Malic acid is an organic acid obtained from Kreb's cycle.
2. The amount of CO₂ released is measured using the respiration quotient (R.Q.).
3. R.Q. can be defined as the ratio of the amount of CO₂ released to the amount of O₂ consumed during respiration.
4. Organic acid such as malic acid contains more oxygen than carbohydrates hence its R.Q. is greater than one, so less O₂ is required for oxidation.

The Chemical formula of malic acid is C₄H₆O, and its respiratory oxidation reaction is as follows:

C₄H₆O₅+3O₂ ⇢ 4CO₂+3H₂O

R.Q. =4CO₂/3O₂=1.33

Hence the amount of carbon dioxide released is 1.33 times more than the oxygen consumed when malic acid is a respiratory substrate.