What type of metabolic reaction requires energy input?

The type of metabolic reaction that requires energy input is endergonic reactions. These reactions are characterized by an increase in free energy, meaning they cannot proceed without an input of energy from an external source. In biochemical terms, endergonic reactions often involve the formation of complex molecules from simpler ones, such as the synthesis of glucose during photosynthesis or the formation of ATP from ADP and inorganic phosphate.

The requirement for energy input is what differentiates endergonic reactions from exergonic reactions, which release energy as they proceed. Catabolic reactions are typically exergonic as they break down molecules, releasing energy that can be harnessed for cellular processes. Oxidative reactions can be either energy-releasing or requiring energy depending on the context; they are more about the transfer of electrons than the overall energy flow of the reaction. Overall, endergonic reactions represent a crucial aspect of anabolism and other cellular processes that build and maintain cellular structures and functions.