Q8 / 200 · MHT CET - Medical 2026 (22 April Shift 2) · Biology
Which one of the following respiratory reactions does NOT yield $\text{CO}_2$?
- APyruvic acid $\rightarrow$ Acetyl Co.A
- BPyruvic acid $\rightarrow$ Acetaldehyde
- Correct answerCPyruvic acid $\rightarrow$ Lactic acid
- DPyruvic acid $\rightarrow$ Ethanol
Solution
In the conversion of pyruvic acid to acetyl CoA (link reaction), oxidative decarboxylation takes place, releasing $\text{CO}_2$.
In alcoholic fermentation, pyruvic acid is first converted to acetaldehyde, releasing $\text{CO}_2$, which is then reduced to ethanol. Thus, the overall conversion of pyruvic acid to ethanol also yields $\text{CO}_2$.
In lactic acid fermentation, pyruvic acid (a 3-carbon compound) is directly reduced to lactic acid (also a 3-carbon compound) by the enzyme lactate dehydrogenase. Since there is no loss of carbon atoms, no decarboxylation occurs and no $\text{CO}_2$ is produced.
Answer: Pyruvic acid $\rightarrow$ Lactic acid
In alcoholic fermentation, pyruvic acid is first converted to acetaldehyde, releasing $\text{CO}_2$, which is then reduced to ethanol. Thus, the overall conversion of pyruvic acid to ethanol also yields $\text{CO}_2$.
In lactic acid fermentation, pyruvic acid (a 3-carbon compound) is directly reduced to lactic acid (also a 3-carbon compound) by the enzyme lactate dehydrogenase. Since there is no loss of carbon atoms, no decarboxylation occurs and no $\text{CO}_2$ is produced.
Answer: Pyruvic acid $\rightarrow$ Lactic acid
Hence, the correct answer is option: 'C'.