Lesson Plan

• Describe diffusion as the net movement of particles down a concentration gradient caused by random motion.
• Explain the key factors that influence the rate of diffusion.
• Interpret the conceptual diffusion flux equation and relate each term to biological examples.
• Apply knowledge of diffusion to explain gas exchange in alveoli and other physiological processes.
• Evaluate how changes in temperature, surface area, or distance affect diffusion rates.

• Projector or interactive whiteboard
• Slide presentation with diagrams (diffusion gradient, alveolus)
• Printed worksheet with concept questions and practice problems
• Alveolus diagram or 3‑D model
• Markers and whiteboard
• Stopwatch/timer for timed activities

Begin with a quick demonstration: release a drop of perfume in the classroom and ask students what they observe. Connect this to prior knowledge of particle motion and concentration differences. Explain that today they will identify how diffusion works and what factors control its speed, with success measured by their ability to explain and apply the concept in biological contexts.

1. Do‑now (5') – Students write a brief description of a real‑life example of diffusion they have seen.
2. Mini‑lecture (10') – Present definition, random motion, and net movement using slides and the alveolus diagram.
3. Guided activity (12') – Small groups analyse the factors table, rank factors by impact, and justify their choices.
4. Equation exploration (8') – Introduce the diffusion flux equation, discuss each term, and solve a simple conceptual problem.
5. Demonstration & discussion (10') – Show a diffusion demo (e.g., food coloring in water) and link observations to the factors.
6. Formative check (5') – Quick exit ticket: list two factors that would double the diffusion rate and why.

Summarise that diffusion is a passive process driven by random particle motion and modulated by several physical factors. Ask students to complete an exit ticket stating one way they could increase diffusion in a biological system. Assign a short homework: research a medical scenario where impaired diffusion is critical and prepare a brief summary.