Advanced Placement (AP) Biology Practice Exam

How is an endergonic reaction defined?

1. It requires energy input to proceed

2. It releases energy to the surroundings

3. It occurs spontaneously without energy

4. It is an energy-releasing process

The correct answer is: It requires energy input to proceed

An endergonic reaction is characterized by the requirement of energy input for the reaction to proceed. This type of reaction results in a net gain of free energy, meaning that the products have a higher energy content than the reactants. Because these reactions do not occur spontaneously, they rely on an external source of energy, such as light or chemical energy, to drive the process forward. In contrast, reactions that release energy, occur spontaneously, or are energy-releasing processes would not be classified as endergonic. Understanding the fundamental energy dynamics of endergonic reactions is crucial in various biological contexts, such as photosynthesis, where plants capture sunlight to produce glucose from carbon dioxide and water, illustrating how energy conversion is essential for life.