Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R

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Question

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: ATP is used at two steps in glycolysis.
Reason R: First ATP is used in converting glucose into glucose-6-phosphate and second ATP is used in conversion of fructose-6-phosphate into fructose-1,6-diphosphate.
In the light of the above statements, choose the correct answer from the options given below:
(1) Both A and R are true but R is NOT the correct explanation of A.
(2) A is true but R is false.
(3) A is false but R is true.
(4) Both A and R are true and R is the correct explanation of A.

Accepted Answer

Correct Answer: D — Both A and R are true and R is the correct explanation of A.Step-by-step Solution:Assertion A (True): During the preparatory (energy investment) phase of glycolysis, two ATP molecules are consumed per molecule of glucose.Reason R (True and explanatory): The two ATP-consuming steps are: (1) Glucose → Glucose-6-phosphate, catalysed by hexokinase (1 ATP consumed); and (2) Fructose-6-phosphate → Fructose-1,6-bisphosphate, catalysed by phosphofructokinase-1 (PFK-1) (1 ATP consumed). These two phosphorylation steps constitute the energy investment phase of glycolysis. The reason precisely and correctly identifies these two steps, thus explaining why ATP is used at exactly two steps. R is the correct explanation of A.Key Concepts:Glycolysis (EMP pathway): Occurs in the cytoplasm; converts glucose (C6) to 2 pyruvate (C3); net yield: 2 ATP + 2 NADH per glucose.Energy investment phase (steps 1–3): 2 ATP consumed (hexokinase and PFK-1 reactions).Energy payoff phase (steps 6–10): 4 ATP + 2 NADH produced per glucose (substrate-level phosphorylation).Net ATP per glucose in glycolysis = 4 − 2 = 2 ATP; Net NADH = 2.

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