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Simple Diffusion vs. Facilitated Diffusion: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on November 22, 2023
Simple diffusion is the passive movement of molecules from high to low concentration, while facilitated diffusion requires transport proteins.

Key Differences

Simple diffusion involves molecules moving passively from a region of higher concentration to lower concentration. Facilitated diffusion, however, involves the same movement, but it requires the assistance of membrane proteins.
Simple diffusion does not require energy and moves molecules such as oxygen or carbon dioxide directly through the cell membrane. In contrast, Facilitated diffusion requires specific transport proteins like channel or carrier proteins but still doesn’t require energy.
In simple diffusion, small, nonpolar molecules move freely across the lipid bilayer. Facilitated diffusion is used for larger or polar molecules that cannot diffuse through the membrane without help.
Simple diffusion is a more basic form of transport, relying on the natural kinetic energy of molecules. Facilitated diffusion is more complex, involving protein structures that provide a passageway or carry molecules across the membrane.
Simple diffusion is limited by the concentration gradient and the nature of the molecule. Facilitated diffusion, while also driven by a concentration gradient, expands the range of molecules that can pass through the membrane by using specific proteins.

Comparison Chart


Passive transport directly through the membrane
Passive transport via specific transport proteins

Energy Requirement

No energy required
No energy required

Types of Molecules

Small, nonpolar molecules
Larger, polar, or charged molecules

Involvement of Proteins

No proteins involved
Requires channel or carrier proteins

Dependence on Concentration Gradient

Moves down the concentration gradient
Moves down the concentration gradient, facilitated by proteins

Simple Diffusion and Facilitated Diffusion Definitions

Simple Diffusion

Movement of molecules from higher to lower concentration without energy use.
Oxygen entering a cell from the bloodstream occurs through simple diffusion.

Facilitated Diffusion

A concentration gradient-driven process aided by membrane-bound proteins.
The transport of calcium ions into muscle cells occurs through facilitated diffusion.

Simple Diffusion

Direct passage of substances across a cell membrane without assistance.
Simple diffusion allows ethanol to be absorbed quickly into the bloodstream.

Facilitated Diffusion

Transport mechanism for molecules that cannot directly diffuse through the membrane.
Facilitated diffusion is used for the entry of water-soluble vitamins into cells.

Simple Diffusion

Passive transport of molecules across a membrane along a concentration gradient.
Carbon dioxide, produced in cells, leaves the body via simple diffusion.

Facilitated Diffusion

Movement of molecules from high to low concentration via specific protein channels.
Ions like potassium move into cells through facilitated diffusion using ion channels.

Simple Diffusion

Natural movement of small, nonpolar molecules across a permeable barrier.
In simple diffusion, water vapor in the air enters a leaf through its stomata.

Facilitated Diffusion

Passive transport process using carrier proteins for larger or polar molecules.
Amino acids are often transported into cells through facilitated diffusion.

Simple Diffusion

A fundamental process where molecules spread from an area of high to low concentration.
The scent of perfume spreading in a room is an example of simple diffusion.

Facilitated Diffusion

Transport of substances across a cell membrane with the help of transport proteins.
Glucose enters cells through facilitated diffusion using glucose transporters.


What is simple diffusion?

It's the passive movement of molecules from a higher to a lower concentration area.

How does facilitated diffusion differ from simple diffusion?

Facilitated diffusion requires special transport proteins, unlike simple diffusion.

Do both simple and facilitated diffusion require energy?

No, both processes are passive and do not require energy.

How do carrier proteins work in facilitated diffusion?

They bind to specific molecules and change shape to transport them across the membrane.

Does temperature affect simple diffusion?

Yes, higher temperatures generally increase the rate of simple diffusion.

Are transport proteins in facilitated diffusion specific to one type of molecule?

Often, yes, they are usually specific to certain substances.

What role do proteins play in facilitated diffusion?

Proteins act as channels or carriers to help transport substances across the membrane.

Can any molecule use simple diffusion to cross a cell membrane?

Only small, nonpolar molecules can use simple diffusion.

Is facilitated diffusion faster than simple diffusion?

It can be, especially for molecules that can't easily cross the membrane on their own.

Is simple diffusion affected by the concentration gradient?

Yes, it occurs along the concentration gradient, from higher to lower concentration.

Does the size of molecules affect simple diffusion?

Yes, smaller molecules diffuse more easily and quickly.

Can facilitated diffusion be inhibited?

Yes, by blocking transport proteins or depleting energy sources.

Can simple diffusion occur in any cell?

Yes, as long as the cell membrane is permeable to the molecule in question.

What is an example of simple diffusion in the human body?

The exchange of oxygen and carbon dioxide in the lungs.

Can facilitated diffusion occur against a concentration gradient?

No, it only occurs along the concentration gradient.

How is facilitated diffusion regulated?

It's regulated by the availability and activity of transport proteins.

What types of molecules typically undergo facilitated diffusion?

Larger, polar, or charged molecules use facilitated diffusion.

How does facilitated diffusion contribute to homeostasis?

It helps regulate the internal environment by controlled transport of substances.

Can simple diffusion become saturated?

No, it doesn't saturate as it doesn’t involve carrier proteins.

Is simple diffusion a form of active transport?

No, it’s a passive transport process.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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