Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration. This fundamental process drives many biological functions, including oxygen exchange in lungs, nutrient absorption in cells, and signal transmission in neurons.
The difference in concentration between two areas. Particles move down their gradient - from high to low concentration - until equilibrium is reached.
Higher temperatures increase particle kinetic energy, causing faster diffusion. This is why diffusion occurs more rapidly in warm environments.
Membranes can be selectively permeable, allowing only certain particles to pass. Lipid-soluble molecules pass through easily, while large or charged molecules require transport proteins.
When particles are evenly distributed throughout a space, the system reaches equilibrium. Particles continue moving but with no net change in concentration.
J = -D × (ΔC/Δx)
Where J is the diffusion rate, D is the diffusion coefficient, and ΔC/Δx is the concentration gradient. This equation quantifies how factors affecting diffusion rate.
Oxygen diffuses from alveoli into blood, while CO₂ diffuses from blood into alveoli.
Medications must diffuse through tissues to reach their targets.
Nutrients enter cells and waste exits through diffusion and osmosis.
Diffusion across nephron membranes filters blood and reabsorbs nutrients.