What is simple diffusion?

Simple Diffusion

Simple diffusion is a type of passive transport where a substance moves across a membrane from an area of high concentration to an area of low concentration, without the help of membrane proteins.

Key Characteristics:

• No Energy Required: Unlike active transport, simple diffusion doesn't require cellular energy (ATP). It relies on the concentration gradient.
• Down the Concentration Gradient: Substances move down their concentration gradient, meaning from where they are more concentrated to where they are less concentrated.
• No Membrane Proteins: The process doesn't involve any transport proteins or channel proteins. The substance passes directly through the phospholipid bilayer.

Factors Affecting Simple Diffusion:

• Concentration Gradient: A steeper gradient leads to faster diffusion.
• Temperature: Higher temperatures generally increase the rate of diffusion.
• Molecular Size: Smaller molecules diffuse more quickly.
• Membrane Permeability: More permeable membranes allow faster diffusion. Lipid solubility is very important.
• Surface Area: A larger surface area increases the rate of diffusion.

Examples:

• The movement of oxygen and carbon dioxide across the alveolar membrane in the lungs.
• Absorption of fat-soluble vitamins in the small intestine.