Both (A) and (R) are correct and (R) is the correct explanation of (A).

Glucose enters extrahepatic tissues (like muscle and adipose) via GLUT4 transporters and gets phosphorylated by glucokinase (or predominantly hexokinase in most tissues) to glucose-6-phosphate. Glucose-6-phosphate lacks a specific transporter to exit the cell, effectively trapping it inside for metabolism.

Option Analysis

Option 1: Both (A) and (R) are correct and (R) is the correct explanation of (A)
This is correct. Reason (R) directly explains Assertion (A) by describing the phosphorylation mechanism (glucokinase → glucose-6-phosphate) and the absence of transporters, which prevents glucose exit.​

Option 2: Both (A) and (R) are correct but (R) is not the correct explanation of (A)
Incorrect. (R) precisely explains the trapping via irreversible phosphorylation and transporter absence, so it is the explanation.

Option 3: (A) is correct but (R) is not correct
Incorrect. (R) is factually true: glucokinase (high-Km hexokinase IV) phosphorylates glucose irreversibly in liver and other extrahepatic tissues like pancreas/beta cells; glucose-6-P is trapped due to no membrane transporter.​

Option 4: (A) is not correct but (R) is correct
Incorrect. (A) is true—glucose does get trapped in extrahepatic tissues post-phosphorylation for glycolysis/glycogenesis.

Glucose trapping in extrahepatic tissues is a key concept in molecular biology and carbohydrate metabolism, especially for exams like NEET/GATE Life Sciences. This process ensures cells like muscle and adipocytes retain glucose for energy after uptake via GLUT transporters.

Glucose Phosphorylation Mechanism

Glucokinase (hexokinase IV) in extrahepatic tissues irreversibly converts glucose to glucose-6-phosphate using ATP. This reaction traps glucose inside the cell since glucose-6-phosphate cannot cross the plasma membrane—no specific transporters exist for it.

Why No Exit from Cells?

Unlike liver (with glucose-6-phosphatase for dephosphorylation and GLUT2 bidirectional transport), extrahepatic tissues lack this enzyme. Glucose-6-P enters glycolysis or glycogen synthesis instead, preventing blood glucose re-release.​

Assertion-Reason Breakdown for Exams

• Assertion (A): Accurate—describes the trapping phenomenon.

• Reason (R): Accurate—pinpoints glucokinase’s role and transporter absence.

• Link: (R) causally explains (A), making Option 1 correct.

This matches standard NCERT/NEET syllabi on glycolysis and tissue-specific metabolism. For competitive prep, memorize: Liver releases glucose; others trap it.​