Overview
This lecture explains diffusion, how it works across cell membranes, and the main factors that affect its rate.
What is Diffusion?
- Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
- Molecules move randomly; as a group, they spread out over time until evenly distributed.
- Net movement refers to considering all particles as a group rather than individual particle paths.
- Diffusion can occur in both liquids and gases, such as perfume in air or food coloring in water.
Diffusion and Cell Membranes
- Cell membranes are described as partially permeable, allowing some molecules but not others to pass through.
- Small dissolved molecules like water, glucose, and amino acids can diffuse through cell membranes.
- Large molecules (e.g., proteins, starch) cannot fit through the membrane.
- Diffusion is a passive process and does not require energy from the cell.
Factors Affecting the Rate of Diffusion
- The concentration gradient: A larger difference in concentration increases the rate of diffusion.
- Temperature: Higher temperatures lead to faster particle movement, increasing diffusion rate.
- Surface area: A larger surface area allows more particles to diffuse at once, raising the overall diffusion rate.
Key Terms & Definitions
- Diffusion — Net movement of particles from high concentration to low concentration.
- Net Movement — The overall movement of all particles considered together.
- Partially Permeable Membrane — A barrier that lets only specific small molecules pass through.
- Concentration Gradient — The difference in particle concentration between two areas.
- Passive Process — A process not requiring cellular energy input.
Action Items / Next Steps
- Review definitions and examples of diffusion.
- List three factors affecting diffusion and give examples of each.