Difference Between Simple Diffusion and Facilitated Diffusion (With Table)

Whoever studied biology has come across the term diffusion. The term diffusion is referred to as the movement of anything (for instance, molecules, ions, energy, atoms) from a region of higher to lower concentration. This process is driven with the help of a gradient in concentration. The concept of diffusion is not limited to biology but is also accepted in many fields, such as chemistry, sociology, physics, finance, and economics. Based on the absence or presence of facilitator molecules, diffusion can be divided into simple diffusion and facilitated diffusion. 

Simple Diffusion vs Facilitated Diffusion 

The main difference between simple and facilitated is that simple diffusion is a process that transports molecules from higher to lower concentrations without the support of transmembrane proteins. On the other hand, facilitated diffusion is a process without the aid of carrier final proteins that transports molecules across the membrane from higher to lower concentrations.  

In simple diffusion, solutes in a solution move along a concentration gradient or across a semipermeable membrane. It is generally carried out with the help of hydrogen bonds which forms between water molecules and solutes. Hydrogen bonds are temporary, but as a result, a solution is constantly stirred.  

In facilitated diffusion, the substance is transported across a biological membrane from higher to lower concentrations. Chemical energy is not directly required due to the movement of substances along the concentration gradient’s direction. Gas transport, ion transport, and glucose and amino acid transport are a few of the examples that entail facilitated diffusion. 

Comparison Table Between Simple Diffusion and Facilitated Diffusion 

Parameter of ComparisonSimple DiffusionFacilitated Diffusion
InterpretationIt is a process that transports molecules from higher to lower concentrations without the support of transmembrane proteins.It is a process without the aid of carrier final proteins that transports molecules across the membrane from higher to lower concentrations.  
ProcessPassive processThe active or passive process
SpeedRelatively slowComparatively fast
Energy from ATPDoes not requireMay, or may not require
Solute specificNoAlways

What is Simple Diffusion? 

In simple diffusion, there is no need for membrane proteins assistance. The substance or particle moves from a higher concentration to a lower one, but the downhill movement of particles does not require membrane protein. In maintaining equilibrium simple diffusion is pivotal.  

Simple diffusion is one of the types of passive transport, and for the proceeding of the process, it does not require chemical energy (ATP). In biological systems, ATP does not drive directly simple diffusion. Concentration gradient and kinetic energy fuel up simple diffusion.  

In simple diffusion, molecules are in random constant motion due to struck of molecules with each other. Pedesis is called when the collision of particles occurs. The molecules are compacted when the area is concentrated. As a result, the motion also reduces. Thus, molecules move towards the larger space or when there is the availability of larger space.  

In biological systems, it can be exemplified by the simple molecular transportation at the cellular level. The feature of the plasma membrane, namely the bilipid membrane prevents the exit and entry of all molecules. In simple diffusion, not all molecules can diffuse freely. 

What is Facilitated Diffusion? 

In facilitated diffusion, transportation includes the passive movement of a molecule with its respective concentration gradient and is directed by the presence of another molecule. After all, the molecules of facilitated diffusion move with their concentration gradient they do not directly involve high-energy molecules such as guanosine triphosphate (GTP) or adenosine triphosphate (ATP).

Across the cell membrane, small non-polar molecules diffuse easily. Lipids have a hydrophobic nature which makes up cell membranes, whereas ions and polar molecules cannot do so. As a result, through transport proteins, they diffuse across the membrane.  

There are mainly three types of transport proteins involved in facilitated diffusion:  

  1. Carrier protein- It is particular for an ion, molecule, or group of substances. It carried the molecule or ion by changing shape over the membrane.
  2. Gated channel protein- It mainly opens a gate to allow molecules for passing through the membrane. A binding site is located at gated channels that are specific to a given ion or molecule.
  3. Channel protein- In the membrane, it acts like a pore that lets small ions or water molecules quickly. The water channel proteins allow water at a very fast rate to diffuse over the membrane.

Main Differences Between Simple Diffusion and Facilitated Diffusion 

  1. Only small molecules can be transported in simple diffusion. On the other hand, both large and small molecules can be transported with facilitated diffusion.  
  2. The occurrence of simple diffusion is through the phospholipid bilayer or simply in a solution. On the flip side, transmembrane protein facilitated diffusion occurs.  
  3. The rate of simple diffusion is proportional to the membrane permeability and the concentration gradient of the solute molecule, whereas the rate of facilitated diffusion relies upon carrier-mediated kinetics.  
  4. The molecules in simple diffusion pass solely in the gradient concentration direction, whereas in facilitated diffusion, the movement of molecules occurs in opposite and directions of the gradient concentration.
  5. When it comes to facilitator molecules, simple diffusion occurs through the cell membrane, whereas facilitated diffusion occurs through particular facilitator molecules. 

Conclusion 

It can be concluded that simple diffusion and facilitated diffusion are two of the types of diffusion. Both terms are used in biological. They both move from a higher to lower concentration. The net movement of molecules on the side of the cell membrane at the equilibrated state is zero.  

The support of transmembrane proteins does not require in the process of simple diffusion, whereas facilitated diffusion requires the aid of carrier channel proteins. The speed is quite slow in simple diffusion, but the speed is comparatively high in facilitated diffusion. The process is passive in simple diffusion, while it can be active or passive in facilitated diffusion.

References 

  1. https://journals.sagepub.com/doi/pdf/10.3181/00379727-212-43986
  2. https://journals.physiology.org/doi/abs/10.1152/physrev.1990.70.4.1135
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