Energy requiring reactions can occur in biological systems because enzymes allow their coupling to other reactions with

Energy requiring reactions can occur in biological systems because enzymes allow their coupling to other reactions with products of lower free energy than the reactants

Explanation:

Reactions which release energy are exergonic reactions and those that require energy are endergonic reactions. Exergonic reactions are with negative ∆G where the free energy (ability to do a work) of the products is lesser than the free energy of the reactants of the reaction.  

To utilize the energy that is released during exergonic reactions, endergonic reactions couple with exergonic reactions in biological systems.

Exergonic reactions are spontaneous and can be coupled with endergonic reactions because their equilibrium constant remains greater than 1.  

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