Diffusion

Definition

Diffusion is the process through which molecules or particles spread from areas of higher concentration to areas of lower concentration, driven by the random movement of molecules. This natural phenomenon plays a crucial role in various biological and chemical processes, particularly in the movement of substances across membranes, affecting how cells interact with their environment and how substances are transported within organisms.

5 Must Know Facts For Your Next Test

1. Diffusion can occur in gases, liquids, and solids but is most commonly discussed in the context of gases and solutions.
2. In biological systems, diffusion is vital for processes such as nutrient absorption, gas exchange in lungs, and waste removal from cells.
3. Factors affecting the rate of diffusion include temperature, size of the molecules, and the medium through which they are diffusing.
4. Fick's laws describe the quantitative relationship between diffusion flux and concentration gradient, helping predict how substances will move over time.
5. Diffusion can be either facilitated or passive; facilitated diffusion involves specific transport proteins that help larger or polar molecules cross cell membranes.

Review Questions

• How does diffusion contribute to the process of gas exchange in the respiratory system?
  • Diffusion is essential for gas exchange in the respiratory system as oxygen from inhaled air diffuses from areas of higher concentration in the alveoli into the bloodstream, where the concentration is lower. At the same time, carbon dioxide diffuses from the blood into the alveoli to be exhaled. This process occurs quickly due to the thin membranes surrounding alveoli and capillaries, making efficient gas exchange possible for respiration.
• Compare and contrast simple diffusion and facilitated diffusion regarding their mechanisms and significance in cellular processes.
  • Simple diffusion occurs directly across the lipid bilayer without any assistance from proteins, allowing small nonpolar molecules like oxygen and carbon dioxide to pass easily. In contrast, facilitated diffusion involves specific channel or carrier proteins that help transport larger or polar molecules like glucose across the membrane. Both processes are vital for maintaining cellular homeostasis by regulating the internal environment of cells, but facilitated diffusion allows for more controlled and selective transport.
• Evaluate how changes in temperature and molecular size can affect the rate of diffusion across a membrane.
  • Changes in temperature directly influence the kinetic energy of molecules; as temperature increases, molecules move faster, which generally increases the rate of diffusion. Additionally, smaller molecules can diffuse more quickly than larger ones due to less steric hindrance when moving through a membrane. Therefore, a higher temperature combined with smaller molecular size creates optimal conditions for rapid diffusion, impacting various biological functions such as nutrient uptake and waste removal.

Related terms

Osmosis: The passive movement of water molecules through a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration.

Concentration Gradient: A difference in the concentration of a substance across a space, which drives the movement of that substance during diffusion.

Permeability: The ability of a membrane to allow substances to pass through it, which is essential for understanding diffusion across biological membranes.