Diffusion of Gases

Diffusion is the primary mode of transport in plants. It is a crucial photosynthesis process in which carbon dioxide diffuses from the stomata into the leaves and then into the cells. Furthermore, water and oxygen diffuse from the leaves into the environment during transpiration. 

Diffusion is a slow process that occurs mostly in gases and liquids. Temperature, pressure, concentration gradient, the permeability of the separating membrane and all other factors  influence diffusion rate.

Types of diffusion

There are three kinds of diffusion as listed below:-  

1. Simple diffusion
2. Facilitated diffusion
3. Channel diffusion

Simple Diffusion  

Simple diffusion is an example of passive transport. It occurs when electrochemical potentials on both sides of a permeable barrier vary. In this type of diffusion, very small molecules can move through gaps.

It usually occurs between the various phospholipid molecules in the cell membranes. Inhibitor molecules do not hinder simple diffusion.

Simple diffusion does not require any energy and has a very low speed. It does not involve protein transporters.

In this type of diffusion, the movement of particles takes place with the direction of a concentration gradient.E.g., water, oxygen, carbon dioxide, etc.

More examples of simple diffusion are:-

• 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 from the lungs transfers into the blood. Also, oxygen transfers into the muscles from the blood cells.  
• Another simple diffusion example- In the body of pregnant women, food and oxygen travels from the mother’s body into the foetus.
• Bacteria have single-celled microorganisms. Bacteria deliver water, oxygen and nutrients to the cytoplasm. No specialised organelles in bacteria perform this type of activity.

Facilitated Diffusion

This type of diffusion is the transport of substances or molecules across a permeable membrane through a concentration gradient. Only large polar molecules pass through this type of diffusion. Examples include amino acids, glucose, etc.

Unlike simple diffusion, this process requires support from transmembrane proteins, which function as facilitator molecules. Two types of proteins help in this type of diffusion: carrier and channel.

In this type of diffusion, the kinetics of carrier-mediated transport affects diffusion rate.

Examples of this type of diffusion are:-

• Glucose (sugar molecule) is the main energy source for cells. Outside of a cell, the bloodstream constantly supplies glucose. Once inside the cell, this glucose is continuously consumed.
• Molecules flow from high to low- Some molecules cannot enter/exit a cell during diffusion. So, this type of diffusion can check some of these molecules while passing through the plasma membrane. They bind the molecules to special carrier proteins by opening channels between the cells.

Channel Diffusion

When the materials pass through one end, the ion channels open in channel diffusion. A protein channel carries out this diffusion, 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.

Some examples of channel diffusion are:-

• The perfume is diffusing into the surrounding (air).
• When watering the plants, the water diffuses into the plant. It checks the leaves from wilting. The leaves take up carbon dioxide from the air (between the mesophyll cells) and transfer it to the chloroplast.
• Diffusion of waste products, salts and water in the kidneys.
• Gaseous exchange in lungs.
• Dialysis is an artificial process that partially replaces renal function.

Factors Affecting Diffusion

• Temperature
• Concentration difference
• Electrical potential
• Osmosis pressure

Diffusion in Plants

• Diffusion of gases takes place in the plants through the leaves.
• Intake of water takes place through the roots by osmosis.
• Transport of biomolecules and minerals in plants.

Everyday Examples of Diffusion

• Adding boiling water to dried noodles
• During worship, we use an incense stick
• Sugar gets dissolved evenly in water

Applications of Diffusion

• Absorption of drugs released in the body (tablets, powder, ointment, etc.)
• Excretion process through kidneys
• Changes of gases in alveoli (lungs)

Conclusion

Diffusion results in a progressive blending of materials. The diffusion process will finally lead to a complete mixing in a phase with constant temperature and no external net forces acting on the molecules. 

Diffusion has applications in various fields, such as biology and chemistry. It explains the exchange of substances for necessary life processes, including medicine absorption to oxygen, carbon dioxide and nitrogen change in alveoli, various food organisations, etc. 

Fick’s law explains the principle of diffusion in liquids but limits solid diffusion as it was not possible during that time.