Diffusion and Factors Affecting Its Rate

Definition of Diffusion

• Diffusion: Movement of material from a region of high concentration to a region of low concentration.
• Example: Oxygen diffusing across a cell's semi-permeable membrane.
  • Oxygen flows from high concentration outside the cell to low concentration inside the cell.
  • Movement occurs down the concentration gradient.

Factors Affecting Rate of Diffusion

1. Concentration Gradient

• Difference in Concentration: The difference between the concentration of O2 outside and inside the cell.
  • As this difference (concentration gradient) increases, the rate of diffusion increases.
  • Proportional Relationship: Magnitude of concentration gradient is directly proportional to the rate of diffusion.

2. Temperature

• Effect of Temperature:
  • Higher temperatures increase the rate of diffusion.
  • Gas molecules have more kinetic energy at higher temperatures, leading them to move faster.
  • Faster movement results in higher rates of diffusion across the cell membrane.

3. Molar Mass of Particles

• Inversely Related:
  • As molar mass increases, the rate of diffusion decreases.
  • Heavy molecules move slowly; lighter molecules move faster.
• Example:
  • Oxygen (O2) vs. Carbon Dioxide (CO2):
    • O2 has a lower molar mass (32 g/mol) compared to CO2 (44 g/mol).
    • O2 diffuses at a higher rate than CO2, assuming other conditions are equal.

4. Surface Area

• Effect of Surface Area:
  • Increased surface area allows more gas particles to flow through.
  • Larger surface area results in a higher rate of diffusion.

5. Thickness of the Membrane

• Inversely Related:
  • As thickness of the membrane increases, the rate of diffusion decreases.
  • Thicker membranes increase the distance gas particles must travel, reducing diffusion rate.

Summary

• Factors influencing the rate of diffusion include concentration gradient, temperature, molar mass, surface area, and membrane thickness.
• Understanding these factors helps in predicting how substances move across cell membranes.