Diffusion: The Movement of Molecules

Diffusion is the spontaneous process by which molecules move from high-concentration areas to low-concentration areas. This movement occurs due to the random motion of molecules, which is more pronounced at higher temperatures.   

Key characteristics of diffusion:

  • Concentration gradient: Diffusion occurs along a concentration gradient, from areas of higher concentration to areas of lower concentration.

  • Net movement: While individual molecules may move in both directions, the net movement is always from higher to lower concentration.

  • Equilibrium: Diffusion continues until the molecules are evenly distributed throughout space, reaching a state of equilibrium.

  • Passive transport: Diffusion is a type of passive transport because it does not require energy input from the cell.

Examples of diffusion:

  • Gas exchange: Diffusion is the primary mechanism for gas exchange in organisms, such as the movement of oxygen from the lungs into the blood and the movement of carbon dioxide from the blood into the lungs.

  • Nutrient absorption: Diffusion allows for the absorption of nutrients from the small intestine into the bloodstream.   

  • Waste removal: Waste products can be removed from cells through diffusion.

Facilitated diffusion:

  • Transport proteins: Facilitated diffusion involves the use of transport proteins embedded in the cell membrane to facilitate the movement of molecules.

  • Selective transport: Transport proteins are specific to certain molecules, allowing for the selective transport of substances across the membrane.

  • Passive process: Facilitated diffusion is also a type of passive transport, as it does not require energy input.

In summary, diffusion is a fundamental process that drives the movement of molecules in various biological systems. 




Osmosis: The Movement of Water

Osmosis is a specific type of diffusion that involves the movement of water from areas with a lower concentration of solutes (and thus a higher concentration of water) to areas with a higher concentration of solutes (and thus a lower concentration of water).