Final answer:
An endergonic reaction requires an input of energy to proceed, while an exergonic reaction releases energy. These reactions can be coupled together to change the overall free energy change. By coupling an exergonic process to an endergonic reaction, the overall reaction can become exergonic or favourable.
Step-by-step explanation:
An endergonic reaction is a reaction that requires an input of energy to proceed. On the other hand, an exergonic reaction is a reaction that releases energy. These reactions can be coupled together to change the overall free energy change. By coupling an exergonic process to an endergonic reaction, the overall reaction can become exergonic or favourable. For example, ATP phosphorylation is an endergonic reaction that requires an input of energy. However, this reaction can be coupled with exergonic reactions, such as catabolism, to make the overall reaction exergonic. Similarly, the exergonic reaction of ATP dephosphorylation can be coupled with the endergonic reaction of polysaccharide formation to change the overall free energy change. This coupling of reactions allows energy released from exergonic reactions to drive endergonic reactions, ensuring that energy is efficiently utilized in living systems.