Question

Assertion :Glycolysis is the first step of respiration in which glucose completely breaks into $C{O}_2$ and $H_{2}O$. Reason: In this process, there is net gain of twenty four molecules of ATP.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect.

Answer 1

Answer: (D)

Glycolysis is the process of breakdown of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of enzyme mediated reactions, releasing energy (ATP) and reducing power $\left(NAD{H}_2\right)$. It is the first step of respiration, which occurs inside the cytoplasm and is independent of $O_2$. In glycolysis, two molecules of ATP are consumed during double phosphorylation of glucose to form fructose $1,6$ diphosphate. Four molecules of ATP are produced in the conversion of $1,3$-diphosphoglycerate to $3$-phosphoglycerate and phosphoenolpyruvate to pyruvate whereas, two molecules of $NAD{H}_2$ are formed during oxidation of glyceraldehyde $3$-phosphate to $1,3$-diphosphoglycerate. Since, each NADH is equivalent to $3$ ATP, so net gain in glycolysis is $8$ ATP.