Q.97  Glucose monomers are joined together by glycosidic linkages to form a cellulose polymer.
During this process, changes in the free energy, total energy, and entropy respectively are
represented correctly by which ONE of the following options?
(A) +ΔG, +ΔH, +ΔS. (B) +ΔG, –ΔH, –ΔS.
(C) –ΔG, +ΔH, +ΔS. (D) +ΔG, +ΔH, –ΔS.

The correct answer is (B) +ΔG, -ΔH, -ΔS.​

Polymerization of glucose monomers into cellulose via glycosidic linkages is a condensation reaction that eliminates water, reducing molecular freedom and disorder. This process is endergonic overall, requiring energy input in biological systems despite a favorable enthalpy from bond formation.​

Option Analysis

• (A) +ΔG, +ΔH, +ΔS: Incorrect. Enthalpy decreases (ΔH negative) due to strong glycosidic bond formation, and entropy decreases (ΔS negative) as monomers form an ordered polymer.​

• (B) +ΔG, -ΔH, -ΔS: Correct. Free energy increases (+ΔG, non-spontaneous), enthalpy decreases (-ΔH, exothermic bond making), but entropy sharply decreases (-ΔS, fewer molecules), dominating via ΔG = ΔH – TΔS.​

• (C) -ΔG, +ΔH, +ΔS: Incorrect. ΔG is positive, not spontaneous without coupling; ΔH is negative, not positive.​

• (D) +ΔG, +ΔH, -ΔS: Incorrect. ΔH is negative from net bond energy gain outweighing water formation.​

Cellulose, Earth’s most abundant biopolymer, forms when glucose monomers link via β-1,4-glycosidic bonds in a dehydration process. This polymerization drives plant cell walls but follows specific thermodynamic rules key for CSIR NET Life Sciences. Free energy (ΔG) rises positively, making it non-spontaneous without enzymes and UDP-glucose activation.​

Thermodynamic Changes

Enthalpy (ΔH) drops negatively as covalent glycosidic bonds form, releasing energy, though water formation slightly offsets this. Entropy (ΔS) falls negatively since many free glucose units become one rigid chain, slashing disorder. Overall, -TΔS term outweighs -ΔH, yielding +ΔG.​

• +ΔG: Endergonic; couples to ATP hydrolysis in vivo.

• -ΔH: Exothermic bond formation dominates.

• -ΔS: Order increases in polymer.

Biological Context

Plants use cellulose synthase to add activated glucose, overcoming +ΔG. Hydrolysis reverses this (exergonic, -ΔG).​

This matches CSIR NET/GATE patterns on biomolecule energetics.​