Overview
This lecture covers the definition of diffusion, its role in and across cell membranes, and the main factors affecting its rate.
What is Diffusion?
- Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
- Particles move randomly, resulting in an overall spreading out until evenly distributed.
- Diffusion occurs in both gases (e.g., perfume in air) and liquids (e.g., food coloring in water).
Diffusion and Cell Membranes
- Diffusion can happen across partially permeable membranes, like cell membranes.
- Partially permeable means only some molecules (usually small and dissolved) can pass through.
- Small molecules such as water, glucose, and amino acids can diffuse through cell membranes.
- Large molecules, like proteins and starch, cannot diffuse through because they are too big.
- Diffusion is a passive process and does not require energy from the cell.
Factors Affecting the Rate of Diffusion
- A larger concentration gradient (greater difference in concentration) increases the rate of diffusion.
- Higher temperature gives particles more energy, making them move faster and diffuse more quickly.
- A larger surface area allows more particles to diffuse at once, increasing the rate of diffusion.
Key Terms & Definitions
- Diffusion — Net movement of particles from high to low concentration.
- Net movement — Total movement of all particles considered together as a group.
- Partially permeable membrane — A barrier that allows only certain small molecules to pass through.
- Concentration gradient — The difference in concentration between two areas.
- Passive process — A process that does not require energy from the cell.
Action Items / Next Steps
- Review definitions and factors affecting diffusion for understanding and memorization.