Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration. This movement occurs because of the random motion of molecules, driven by the second law of thermodynamics, which states that systems tend to move toward a state of greater entropy or disorder.
How diffusion works:
- Concentration gradient: Diffusion occurs when there is a difference in the concentration of a substance between two areas. This difference is called a concentration gradient.
- Random movement: Molecules are constantly in motion, bumping into each other and changing direction. This random movement causes them to spread out over time.
- Net movement: Although molecules move randomly, there is a net movement from the area of higher concentration to the area of lower concentration. This is because there are more molecules in the higher concentration area, and therefore more of them are likely to move to the lower concentration area.
Examples of diffusion in biology:
- Oxygen transport: Oxygen diffuses from the lungs into the bloodstream, and then from the bloodstream into the cells of the body.
- Carbon dioxide transport: Carbon dioxide diffuses from the cells of the body into the bloodstream, and then from the bloodstream into the lungs.
- Nutrient uptake: Plants absorb nutrients from the soil through diffusion.
- Waste removal: Waste products from cells diffuse into the bloodstream and are then removed by the kidneys.
Factors affecting diffusion rate:
- Concentration gradient: The steeper the concentration gradient, the faster the rate of diffusion.
- Temperature: Higher temperatures increase the rate of diffusion because molecules move faster.
- Surface area: A larger surface area allows for more molecules to diffuse across the membrane.
- Distance: The shorter the distance, the faster the rate of diffusion.
- Molecular size: Smaller molecules diffuse faster than larger molecules.
- Membrane permeability: The more permeable the membrane, the faster the rate of diffusion.
Practical applications of diffusion:
- Drug delivery: Drugs are often designed to be absorbed through diffusion across cell membranes.
- Food preservation: Salting and sugaring foods prevent bacterial growth by creating a concentration gradient that draws water out of the bacteria.
- Wastewater treatment: Diffusion is used to remove pollutants from wastewater.
