Final answer:
Coupling energetically unfavourable (endergonic) and favourable (exergonic) reactions allows cells to drive non-spontaneous processes, like ATP synthesis, by using energy released from favourable reactions.
Step-by-step explanation:
Coupling energetically unfavourable reactions with energetically favourable reactions yields a biologically useful way to drive non-spontaneous processes. This phenomenon is essential in life processes, such as cellular respiration and photosynthesis, where high-energy compounds like ATP are synthesized through the coupling of exergonic and endergonic reactions. Exergonic reactions release energy and have a negative change in free energy (ΔG < 0), making them spontaneous, whereas endergonic reactions require an input of energy and have a positive ΔG. By coupling these two types of reactions, cells can utilize the energy released from exergonic reactions to power the endergonic ones, effectively overcoming the energy barrier required for the latter to proceed.