Diffusion, Osmosis, and Transport Mechanisms

Introduction

• Discusses diffusion, osmosis, passive and active transport, and facilitated diffusion.

Diffusion

• Definition: Movement of material from high to low concentration.
• Example: O2 and CO2 moving through a phospholipid bilayer.
• Nature: Passive transport (does not require energy).
  • Analogy: A ball rolling down a hill without energy input.

Passive vs Active Transport

• Passive Transport
  • Movement from high to low concentration.
  • Does not require energy.
• Active Transport
  • Movement from low to high concentration.
  • Requires energy (ATP).
  • Analogy: Pushing a ball up a hill.

Membrane Components

• Phospholipid Bilayer
  • Structure of cellular membranes.
• Ion Channel, Carrier Protein, Aquaporin
  • Allow passage of various molecules.

Specific Examples

• CO2 Diffusion
  • Small, nonpolar, easily diffuses across membranes.
• Sodium Ion Transport
  • Active transport using ATP to pump sodium out of the cell.
  • Sodium-Potassium Pump: Uses ATP to exchange sodium and potassium ions.
• Glucose Transport
  • Facilitated diffusion using a carrier protein.
  • Moves down the concentration gradient.
• Water Movement (Osmosis)
  • Special case of diffusion for water.
  • Uses aquaporin to move from high to low concentration.

Facilitated Diffusion

• Example of passive transport.
• Requires a carrier protein.
• Moves molecules like glucose across membranes.

Osmosis

• Definition: Diffusion of water across a membrane.
• Example: Water moving in a U-tube experiment.
• Driving Forces
  • Osmotic pressure vs. gravitational force.
  • Equilibrium achieved when forces balance.

Summary

• Diffusion: Movement from high to low concentration; passive.
• Osmosis: Special case of diffusion for water.
• Active Transport: Requires energy; moves materials from low to high concentration.

Conclusion

• Understanding of active vs passive transport.
• Distinction between diffusion and osmosis.