Endergonic Reaction: Definition & Examples

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  • 0:01 What Are Endergonic Reactions?
  • 0:47 Photosynthesis
  • 1:41 Metabolic Reactions
  • 2:30 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Chemical reactions take place in nature as well as in living things. These reactions often involve the exchange of energy. In this lesson, we'll study a type of chemical reaction known as an endergonic reaction and look at two examples.

What Are Endergonic Reactions?

Chemical reactions are occurring all around you and inside you. Even as you watch this lesson your stomach is using acid to break down food molecules for digestion; and outside your window, trees and flowers are undergoing photosynthesis, the process plants use to convert sunlight into usable energy. All chemical reactions involve energy.

An endergonic reaction is a reaction that requires energy to be absorbed in order for it to take place. These reactions are not spontaneous. They require work or an input of force - often in the form of energy - to get started. Sometimes the initial energy required to get the reaction started is all the energy that is required, while other times the reaction continues to absorb energy throughout the entire process.


One of the most common examples of an endergonic reaction is the process of photosynthesis. Photosynthesis is used by all plants to convert light energy into a form of chemical energy that can be used to fuel their life processes.

Photosynthesis doesn't happen spontaneously. For example, if you cover a plant with a black garbage bag and you put it in a dark room, it eventually will die. Why do you think this happens? The plant can't spontaneously make food or complete its life processes without an input of light energy to fuel the photosynthesis process. Once a plant emerges from the soil and begins to grow, it depends on light.

It's important to note that plants have all of the materials and organelles for photosynthesis to occur inside them at all times. However, they simply can't complete the process without the input of light energy. This makes photosynthesis an endergonic reaction.

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