Difference Between Simple Diffusion and Facilitated Diffusion

The key difference between simple diffusion and facilitated diffusion is that simple diffusion occurs without the involvement of channel or carrier proteins while the facilitated diffusion occurs through channel or carrier proteins.

Simple diffusion is a process that transports molecules from a region of high concentration to a region of low concentration. It occurs along the concentration gradient. Hence it does not use energy. And, this process can be explained by a simple task where when you open a scent bottle, quickly its smell spreads throughout the room by diffusion.

Similarly, if you put an ink drop into a beaker filled with water, the colour will distribute evenly in the water. Diffusion not only occurs in those instances, but it also occurs in the cells as well. However, sometimes when larger molecules diffuse across the membrane, the proteins associating the membrane involve with the diffusion process. It is referred to as facilitated diffusion, and it differs from the simple diffusion since it involves the membrane proteins which are channels or carrier proteins. However, since both the simple diffusion and facilitated diffusion occur along the concentration gradient, both processes are passive processes.

CONTENTS

1. Overview and Key Difference
2. What is Simple Diffusion
3. What is Facilitated Diffusion
4. Similarities Between Simple Diffusion and Facilitated Diffusion
5. Side by Side Comparison – Simple Diffusion vs Facilitated Diffusion in Tabular Form
6. Summary

What is Simple Diffusion?

Simple diffusion is a process that transports molecules from a region of higher concentration to a region of lower concentration in a solution or across a semi-permeable membrane. It is a passive process. In simple diffusion, molecules move without the aid of other molecules such as proteins or channel or carrier proteins.

Simple diffusion passively occurs until all the molecules distribute evenly throughout the solution or between both sides of the membrane. Hence, this process stops when the equilibrium is reached. Since the simple diffusion does not occur through transmembrane proteins, it occurs via the phospholipid bilayer. Furthermore, simple diffusion can transport only small molecules.

What is Facilitated Diffusion?

Facilitated diffusion is a form of diffusion that facilitates the movement of molecules from a region of higher concentration to a region of lower concentration via transmembrane proteins. Since it also occurs along the concentration gradient, it is a passive process similar to simple diffusion. But, facilitated diffusion occurs through the proteins. Hence, it differs from the simple diffusion.

Moreover, this process facilitates the uptake of nutrients across the cell membrane without utilizing energy. It uses channel proteins or carrier proteins of the membrane. Not only small molecules, but facilitated diffusion also facilitates the movement of larger molecules across the membrane as well. Similar to simple diffusion, facilitated diffusion occurs till the concentration is equal in both sides.

What are the Similarities Between Simple Diffusion and Facilitated Diffusion?

• Simple diffusion and facilitated diffusion are passive processes that do not use energy.
• Both processes occur along the concentration gradient.
• Also, when equilibrium is reached, the molecular movements stop in both processes.
• Furthermore, these processes occur in cells across the membranes.

What is the Difference Between Simple Diffusion and Facilitated Diffusion?

Simple diffusion occurs from a higher concentration to a lower concentration passively. Transmembrane proteins do not involve with the simple diffusion. On the other hand, facilitated diffusion also occurs from higher concentration to lower concentration passively. But transmembrane proteins aid the facilitated diffusion. Therefore, this is the key difference between simple diffusion and facilitated diffusion. Furthermore, simple diffusion takes place across the phospholipid bilayer while the facilitated diffusion takes place only across the membrane proteins. Such that, this is also a difference between simple diffusion and facilitated diffusion.

Another difference between simple diffusion and facilitated diffusion is that the simple diffusion can transport only smaller molecules while the facilitated diffusion can transport both the small and larger molecules across the cell membrane.

The below infographic summarizes the difference between simple diffusion and facilitated diffusion.

Summary – Simple Diffusion vs Facilitated Diffusion

Simple diffusion and facilitated diffusion are two passive processes that allow molecules to distribute from higher concentration to lower concentration. The transmembrane proteins do not support simple diffusion. On the other hand, carrier or channel proteins aid the facilitated diffusion. Thus, it is the key difference between simple diffusion and facilitated diffusion. Furthermore, when considering the cell membrane, simple diffusion occurs via the phospholipid bilayer of the cell membrane while facilitated diffusion occurs via the transmembrane proteins. Thus, this is another difference between simple diffusion and facilitated diffusion. Simple diffusion allows small molecules to travel across the membrane while facilitated diffusion allows both small and larger molecule to pass through the membrane. Thus, this article summarizes the difference between simple diffusion and facilitated diffusion.

Reference:

1.“Facilitated Diffusion.” Wikipedia, Wikimedia Foundation, 6 Nov. 2018. Available here

Image Courtesy:

1.”Scheme simple diffusion in cell membrane-en”By LadyofHats Mariana Ruiz Villarreal – Own work. (Public Domain) via Commons Wikimedia  
2.”Facilitated Diffusion”By Kjaray – Own work, (CC BY-SA 4.0) via Commons Wikimedia