Q.28 Which one of the following need NOT be conserved in a biochemical reaction?
(A) Total mass (B) Total moles
(C) Number of atoms of each element (D) Total energy
Total moles need not be conserved in a biochemical reaction. This multiple-choice question tests fundamental conservation laws in chemistry, applicable to biochemical contexts like enzyme-catalyzed reactions. The correct answer is (B) Total moles, as biochemical reactions often involve changes in the number of molecules despite conserving mass, atoms, and energy.
Option Analysis
(A) Total mass must be conserved per the law of conservation of mass, which holds in closed systems for all chemical reactions, including biochemical ones where reactants equal products in mass. Biochemical reactions, such as glycolysis, balance total mass across all steps.
(B) Total moles (or molecules) does not need conservation, as reactions frequently produce more or fewer molecules; for example, one glucose molecule (C6H12O6) yields two pyruvate molecules in glycolysis, changing the mole count.
(C) Number of atoms of each element remains conserved, as chemical equations balance atoms of carbon, hydrogen, oxygen, etc., in biochemical pathways like the Krebs cycle.
(D) Total energy conserves via the first law of thermodynamics, with energy shifting forms (e.g., ATP hydrolysis releases potential energy as heat or work) but totaling unchanged.
In competitive exams like IIT JAM or CSIR NET, questions on conserved in a biochemical reaction test stoichiometry and thermodynamics basics. Biochemical reactions, from metabolism to enzyme kinetics, follow physical laws but differ from simple chemical ones due to complexity.
Why Total Moles Changes
Biochemical reactions often split or combine molecules unevenly. Hydrolysis of ATP (adenosine triphosphate) to ADP + Pi produces two products from one reactant, so moles increase while atoms balance. This distinguishes moles from invariant quantities like mass.
Core Conservation Laws
-
Mass and Atoms: Lavoisier’s law ensures no atom creation/destruction; e.g., photosynthesis balances CO2 + H2O to glucose + O2.
-
Energy: ΔE = q + w holds, vital for bioenergetics like oxidative phosphorylation.
Mastering these aids problem-solving in genetics, biochemistry, and exam prep.
