There are generally considered to be three main types of diffusion in biology. These are: simple diffusion, facilitated diffusion, and osmosis.
These types of diffusion differ primarily in the way substances move across cell membranes.
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Simple Diffusion: This type involves the movement of a substance across a membrane from an area of high concentration to an area of low concentration, without the assistance of membrane proteins. This works well for small, nonpolar molecules like oxygen and carbon dioxide.
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Facilitated Diffusion: This process also involves movement from high to low concentration, but it requires the assistance of membrane proteins. These proteins can be channel proteins (forming a pore) or carrier proteins (binding to the substance and changing shape to transport it). This is used for larger or charged molecules like glucose and amino acids.
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Osmosis: This is the diffusion of water across a semi-permeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
In summary, while the fundamental principle of moving down a concentration gradient remains the same, the mechanisms differ significantly, giving rise to the three recognized types of diffusion in biological systems.
