Lecture Notes: Diffusion and Its Role in Biological Processes

Introduction to Ich Disease

• Ich (Ichthyophthirius multifiliis) is a disease that affects aquarium fish.
• Caused by a parasitic protist.
• Highly contagious among fish.
• Symptoms include white spots on fins, bodies, and gills.
• Can be lethal if untreated.

Treatment of Ich

• Common treatment involves methylene blue, an antiparasitic.
• Directions specify the dosage based on water volume.
• Medication spreads through the water via diffusion.

Understanding Diffusion

• Definition: Diffusion is the net movement of a substance from high concentration to low concentration down its concentration gradient.
• Example: Methylene blue spreading in aquarium water.
• Results in uniform appearance throughout the water.

Characteristics of Diffusion

• Occurs in liquids and gases (e.g., air fresheners).
• Molecules are always in motion, even at equilibrium.
• Diffusion is a passive transport process, requiring no energy input.

Types of Diffusion

• Simple Diffusion: Movement directly through a medium without barriers.
• Facilitated Diffusion: Requires a channel or carrier protein to cross cell membranes; still passive.

Factors Affecting Diffusion Rate

1. Distance: Greater distance slows diffusion rate.
2. Temperature: Higher temperatures increase diffusion rate.
3. Solvent Characteristics: Dense solvents decrease diffusion rate.
4. Molecule Characteristics: Larger mass decreases diffusion rate.
5. Barrier Characteristics: Easier for small, nonpolar substances to pass through cell membranes.
   • Surface area and thickness of barrier affect rate.

Importance of Diffusion in Biological Systems

• Critical for cellular function and survival.
• Example: Oxygen and carbon dioxide exchange in the lungs.
• Essential for the transport of nutrients and waste products in cells.

Conclusion

• Diffusion is a vital process for life, facilitating essential exchanges in biological systems.
• Encouragement to stay curious and continue exploring scientific phenomena.