Simple Diffusion

Diffusion is defined as the net movement of a substance or molecules from a region of higher concentration to a region of lower concentration. It is very useful in the separation of a variety of gases. Diffusion is impossible when the concentration gradients of both regions are the same. For diffusion, we will have to create differentiation between the concentration gradients of two cells. Simple diffusion occurs when electrochemical potentials on both sides of a permeable barrier vary. Some factors affecting diffusion are the size of the molecule, concentration gradient, temperature, and state of matter. Diffusion promotes cellular respiration and distributes nutrients among cells and others.

Types of Diffusion

Simple Diffusion

In simple diffusion, a substance moves from a higher concentration to a lower concentration. It is a means of passive transport. Passive transport means that energy is not needed for the movement of the molecules.

In this type of diffusion, very small molecules can move through gaps. It takes place between the various phospholipid molecules in the cell membranes. The speed of simple diffusion is very low and does not require any energy. 

Inhibitor molecules do not hinder simple diffusion. In this type of diffusion, the movement of particles takes place in the direction of a concentration gradient. Water and oxygen are examples of molecules that use simple diffusion.

Examples of simple diffusion

• Steroid hormones can move freely across different membranes down their concentration gradient. So, this is an excellent example of simple diffusion.
• At the time of food digestion, oxygen is transferred into the blood from the lungs. Also, oxygen is transferred into the muscles from the blood cells. 
• In the body of pregnant women, food and oxygen travel from the mother’s body into the fetus.
• Bacteria have single-celled microorganisms. Bacteria deliver water, oxygen, and nutrients to the cytoplasm. No specialised organelles in bacteria perform this type of activity.
• Dialysis is an artificial process that partially replaces renal function. Dialysis is based on the principle of diffusion of solutes and ultrafiltration of fluid across a semipermeable membrane.

Facilitated Diffusion

The diffusion of a substance depends on its solubility in lipids. A cell membrane is made up of proteins and lipids. Substances that are soluble in lipids will diffuse through the membrane faster. 

However, hydrophilic substances will not easily pass through the membrane. Facilitated diffusion allows these molecules to pass through the membrane. It is the passive movement of molecules across cell membranes (semipermeable) through certain protein channels, from higher to lower concentrations.

Plastids, mitochondria, and some bacteria have certain proteins named porins that allow small molecules to pass across them.

Channel Diffusion

It involves the ions and charged particles moving through a specific channel protein/pore in the cell wall. In this case, no limits exist to the number of particles that travel through each channel.

The channels are very selective and will accept only one type of molecule for transportation. A protein channel carries out this diffusion. It allows the compounds or molecules to go into/out of the cell. 

This type of diffusion is regulated very easily by the proteins. When the materials pass through one end, the ion channels open in channel diffusion. This diffusion is carried out by a protein channel. This is called “channel-mediated diffusion.” 

Proteins that are embedded in the membrane act as a doorway for diffusion. The molecules will move down a concentration gradient via channel diffusion.

Examples of channel diffusion

• Perfume diffusing into the air.
• When watering the plants, the water is diffused into the plant. Carbon dioxide is diffused from the leaves from the air (located between the mesophyll cells) and transfers to the chloroplast of leaves.

Factors Affecting Diffusion

• Temperature: The increase in temperature increases the rate of diffusion.
• Pressure: With the increase in pressure, the rate of diffusion increases.
• Size of molecule or particles: Heavier particles will undergo slow diffusion while light molecules will diffuse faster.
• Concentration gradient: Diffusion occurs from higher to lower concentrations.
• Permeability of the membrane: Diffusion usually does not need a membrane, but for osmosis, a semipermeable membrane is needed. Through a permeable membrane, osmosis cannot take place.

Conclusion

There are various types of diffusion like simple diffusion, facilitated diffusion, dialysis, and osmosis. Some everyday examples of diffusion include adding boiling water to dried noodles, using an incense stick, and dissolving sugar evenly in water.

Diffusion is also involved in a detection technique called the methane detecting process. Osmosis is also part of diffusion, which involves the infiltration of water by a technique called reverse osmosis. In our kitchens, the gas in LPG comes out by diffusion.