Chemical reactions happen all around us inside our bodies, in plants, in the environment and even inside a simple cell. Some reactions give off energy, while others need energy to move forward. The reactions that require energy input are known as endergonic reactions.

If you are just starting to learn biochemistry or trying to understand this topic for your exam, don’t worry. This guide explains endergonic reactions in simple, everyday language and without confusing scientific terms.

What Exactly Is an Endergonic Reaction?

An endergonic reaction is a type of chemical reaction that cannot happen on its own. It needs energy from outside to take place. The word “endergonic” comes from two Greek words:

“Endo” meaning inside
“Ergon” meaning energy or work

So an endergonic reaction is one that takes energy in.

Think of it like charging your phone. Your phone won’t charge unless you plug it in. In the same way, an endergonic reaction won’t happen unless energy is supplied.

Key Points to Remember

It absorbs energy from the surroundings.
It is non-spontaneous (does not start on its own).
Its products have more energy than the starting materials.
It has a positive ΔG (Gibbs free energy).

A Very Simple Way to Understand Endergonic Reactions

Imagine pushing a heavy box up a hill. You must use force to push it upward. Without your effort, the box will simply stay in place.

Endergonic reactions work the same way they require an energy push.

The Basic Formula

Reactants + Energy → Products (with higher energy)

This tiny formula tells you everything:
energy must be added for the reaction to occur.

Why Are Endergonic Reactions Important?

Even though they require energy, endergonic reactions are extremely important especially in living organisms. Your body uses endergonic reactions every second to:

Grow and repair tissues
Make proteins, DNA, and enzymes
Store nutrients and energy
Move muscles
Help nerves send signals

Without these reactions, life would stop instantly.

Endergonic vs Exergonic Reactions (A Simple Comparison)

To understand endergonic reactions better, it helps to look at their opposite: exergonic reactions.

Feature	Endergonic Reaction	Exergonic Reaction
Energy	Absorbed	Released
ΔG Value	Positive (+ΔG)	Negative (–ΔG)
Spontaneous?	No	Yes
Product Energy	Higher	Lower
Example	Photosynthesis	Cellular respiration

A quick way to remember:

Endergonic = Energy In
Exergonic = Energy Exit

Examples of Endergonic Reactions (Explained Simply)

Below are some easy and real-world examples that will help the idea stick.

1. Photosynthesis (The Most Famous Endergonic Reaction)

Plants use sunlight to make food. In this process, they absorb light from the sun and use it to convert carbon dioxide and water into glucose.

6CO₂ + 6H₂O + sunlight → glucose + oxygen

Because sunlight energy is absorbed, this reaction is clearly endergonic.

Think of plants as tiny factories that capture sunlight and store it as chemical energy.

2. Making ATP from ADP + Pi

Inside every cell in your body, ATP acts like a “power packet.” But making ATP itself requires energy.

ADP + Pi + energy → ATP

Since energy must be added, this is another endergonic reaction.

3. Building Proteins

When your body joins amino acids together to form proteins, it needs energy. Each bond formed requires ATP. This makes protein synthesis endergonic.

This is why your body uses more energy when it grows, heals, or builds muscle.

4. Active Transport in Cells

Cells sometimes move molecules from low concentration to high concentration which is like swimming upstream. The cell uses ATP to make this happen.

This process is also energy-dependent and endergonic.

How Do Endergonic Reactions Work?

To understand the working process, let’s go step by step.

Step 1: Reactants Have Low Energy

The starting materials (reactants) contain less stored energy.

Step 2: Energy Must Be Added

The reaction cannot start until energy enters the system.
This energy may come from:

Sunlight
ATP
Heat
Electrical energy
Chemical energy from other reactions

Step 3: Products Have Higher Energy

Once the reaction is complete, the products have more stored energy than the reactants.

This explains why energy absorption is necessary.

Understanding Gibbs Free Energy (ΔG) in Simple Words

Gibbs free energy helps scientists predict whether a reaction will occur naturally.

For endergonic reactions:

ΔG is positive
This means energy must be added
The reaction is not spontaneous

If ΔG were negative, the reaction would occur on its own — but that would make it exergonic.

Why Living Organisms Depend on Endergonic Reactions

Every living thing like plants, animals, humans, even tiny bacteria relies on endergonic reactions to survive.

These reactions help with:

Growth
Reproduction
Energy storage
Repairing damaged cells
Making hormones and enzymes
Movement and muscle activity

Without endergonic reactions, no organism could build the molecules necessary for life.

How Cells Power Endergonic Reactions: ATP to the Rescue

Cells use ATP as their main energy source.
ATP releases energy through an exergonic reaction (breaking ATP → ADP + energy).

Then this released energy is used to drive endergonic reactions.

This combination is called a coupled reaction.

Example of coupling:

ATP breaks down → releases energy
That energy powers protein synthesis (endergonic)

This efficient system ensures that energy is never wasted.

Final Thoughts

Endergonic reactions may sound complicated at first but once you understand the idea of “energy going in” the concept becomes much easier. These reactions are essential for building, repairing, storing and growing everything life needs to function.

Whether you are studying biology, chemistry or preparing for an exam, understanding endergonic reactions gives you a strong foundation for more advanced topics. read more