What is the primary characteristic of an endergonic reaction?

Endergonic reactions are defined by their requirement for energy input to proceed. In these reactions, the products have a higher free energy than the reactants, meaning that energy must be absorbed from the surroundings to drive the reaction forward. This is in contrast to exergonic reactions, where energy is released as the reaction proceeds, causing a net decrease in free energy.

The concept of energy absorption is crucial for understanding how endergonic reactions function in biological systems. For example, in photosynthesis, plants absorb light energy to convert carbon dioxide and water into glucose and oxygen. This illustrates the principle that energy is not only a factor in initiating these reactions but is essential to the overall process itself.

Furthermore, endergonic reactions typically do not occur spontaneously; they require a constant energy source to transform reactants into products. The requirement for activation energy is also misleading in this context, as most chemical reactions need activation energy to begin, regardless of whether they are endergonic or exergonic.

Thus, the defining characteristic of endergonic reactions is the absorption of energy, leading to a rise in free energy within the system.