Differences between simple diffusion and facilitated diffusion

Simple diffusion, facilitated diffusion and active transport are three methods to transport various molecules across a membrane. Whilst similar in the overall effect, there are some major differences between these methods.

1. Energy requirement: simple diffusion and facilitated diffusion are similar in the fact that both are passive processes that require no energy (ATP) since both transport molecules down a concentration gradient. Active transport on the other hand is an active process, thus requiring energy provided through ATP hydrolysis and transports substances against the concentration gradient.

2. Machinery requirements: As simple diffusion is passive, it requires no extra machinery. For both facilitated diffusion and active transport, transmembrane proteins are required. For facilitated diffusion, carrier proteins or channel proteins are used. For active transport, carrier proteins that also act as ATPases are required.

3. Cargo and selectivity: Simple diffusion across a biological membrane is difficult, as the membrane acts as a barrier and prevents anything large or polar to diffuse through, although small, non-polar molecules such as oxygen, carbon dioxide and small hormones like oestrogen can diffuse through non-selectively. Facilitated diffusion and active transport are a lot more selective, requiring very specific transmembrane proteins which in most cases will only be able to transport one specific molecule across the membrane. However, many different types of these proteins exist, allowing a wide array of molecules of varying charges and sizes to be transported. For the transport methods that require carrier proteins (some facilitated diffusion and all active transport), it is even possible to have various activation methods to open the carrier proteins. E.g. voltage gated protein channels involved in action potential generation.

• What is Diffusion?
• Simple and Facilitated Diffusion Examples
  • Simple Diffusion
  • Facilitated Diffusion
• Identify the Similarities between Simple Diffusion and Facilitated Diffusion
• Differences between Simple and Facilitated Diffusion
  • Speed
  • Size of Molecules
  • Driving Force
  • Solute Specificity
  • Energy Requirement
  • Direction of Movement
  • Inhibition
  • Channel Proteins
• Conclusion

What is Diffusion?

The movement of elements from a higher concentration to a lower concentration region is called diffusion. The process works on the passive phenomenon, which means it requires no energy. Besides, the gradient is more than enough to drive the process.

There are typically two types of diffusion processes, which have their similarities and differences. These are further named Simple Diffusion & Facilitated Diffusion.

• Simple Diffusion: It is a type of passive transport of molecules that, as the name suggests, is merely unassisted by transmembrane.
• Facilitated Diffusion: On the other hand, it is the spontaneous transport of molecules or ions across a cell’s membrane. Facilitated diffusion requires specific transmembrane proteins to process in a cell.

We can encounter a variety of examples relating to simple and facilitated diffusion in our daily life.

Simple Diffusion

• Similarly, the phenomenon even runs within a cell, where the chloroplast and mitochondria play a vital role in permitting molecules to pass through it via simple diffusion.
• Moreover, the exchange of gases between lungs and blood, the mixing of gases in the atmosphere, and the absorption of nutrients by bacteria are examples of simple diffusion.

Facilitated Diffusion

• The transfer of glucose in all parts of a body to provide energy follows facilitated diffusion. Since these complex molecules cannot process independently, they require glucose transporters and energy to diffuse. Hence, it falls under facilitated diffusion examples.
• Similarly, the transfer of ions like calcium and potassium within a body runs through this type of diffusion.
• In addition, the movement of oxygen in the blood with the help of hemoglobin and the transport of amino acids from the blood to the cell are examples of facilitated diffusion.

Identify the Similarities between Simple Diffusion and Facilitated Diffusion

The following chart will help you clarify the similarities between both diffusion types.

Simple Diffusion: The membrane is freely permeable to the molecules, so their movement does not require energy utilization.

• Simple diffusion is a type of passive transport, which means no energy is required.
• Furthermore, it works with the concentration gradient, which means it goes from a high concentration area to a low concentration area.

Facilitated Diffusion: In Facilitated diffusion, the membrane is not freely permeable to the molecule, for example, hydrophilic substances. So, their movement across the cell requires specialized proteins, which will help them clear the plasma membrane barrier.

• Facilitated diffusion is also a passive transport type; thus, no energy is required.
• Facilitated diffusion also works with the concentration gradient, going from a high concentration area to a low concentration area.

Differences between Simple and Facilitated Diffusion

It’d be easy to understand the differences if we first glance at a brief comparison table between the two!

Speed

• The simple diffusion speed is relatively low.
• Facilitated diffusion, on the other hand, is somewhat higher concerning speed.

Size of Molecules

• Simple diffusion is primarily occupied in the route of small non-polar molecules.
• In contrast, facilitated diffusion is generally involved in moving large and polar molecules across a biological membrane.

Driving Force

• The simple diffusion driving force is the concentration gradient across the membrane.
• On the other hand, for facilitated diffusion, the distinction in the concentration of solute across the membrane is the driving force.

Solute Specificity

• The cycle of simple diffusion dissemination is not solute explicit.
• On the contrary, facilitated diffusion is directed by the specificity between solute and carrier molecules.

Energy Requirement

• No energy is required because a simple diffusion is a passive transport mechanism.
• Some facilitated diffusion processes are also passive transport mechanisms, but most of them are active. Thus, requiring energy to diffuse.

Direction of Movement

• In simple diffusion, the movement of particles occurs along the path of the concentration gradient.
• In facilitated diffusion, molecules’ movement can happen in the direction and also opposite the concentration gradient.

Inhibition

• An inhibitor molecule does not inhibit simple diffusion.
• In contrast to simple diffusion, specific inhibitor molecules can inhibit facilitated diffusion.

Channel Proteins

• In simple diffusion, the movement of molecules occurs through the general surface of the membrane.
• Gated channel proteins, channel proteins, and also carrier proteins are the main complex transport proteins in facilitated diffusion.

Conclusion

Whether the process is simple or facilitated diffusion, they both demand a concentration gradient. Diffusion comes in several types where these two, simple and facilitated, are the most utilized in routine human body processes. The similarities and differences mentioned above are sufficient for anyone wanting to clear the concepts.

Amna being a Physicist wants to share her subject expertise and knowledge with people. Amna is a highly energetic and motivated lecturer as well.