Which statement is true regarding coupled reactions?

The statement that free energy changes are additive is true regarding coupled reactions. When two or more reactions occur in sequence, the overall free energy change of the combined process is equal to the sum of the free energy changes of each individual reaction involved. This means that if one reaction is energetically unfavorable (has a positive ΔG), it can be coupled to a second reaction that is energetically favorable (has a negative ΔG), such that the overall free energy change for the coupled process is negative. This principle is crucial for understanding how cells drive endergonic processes (which require energy input) by coupling them with exergonic reactions (which release energy), such as the hydrolysis of ATP.

In the context of biochemical pathways, this concept allows for the regulation and efficiency of metabolic processes, as unfavorable reactions can occur in tandem with favorable ones, facilitating various cellular functions and energy transformations. This additive nature is a fundamental principle in bioenergetics and helps explain how living organisms can maintain their necessary energy balance.