Lesson Notes By Weeks and Term v4 - SHS 1

Lesson Video

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Performance objectives

• Explain the processes of osmosis and diffusion.
• Model the osmosis process using everyday materials.
• Identify real-life applications of diffusion and osmosis.
• Conduct a simple experiment to observe these processes.

Lesson summary

This lesson explores osmosis, a fundamental process for life. All living things, from the smallest bacteria to the largest Odum tree, and including ourselves, depend on osmosis to move water in and out of their cells. Understanding this process is key to understanding how we stay hydrated, how plants stand upright, and even how we preserve some of our favourite local foods like 'Koobi'. We will start with a related, simpler process called diffusion before diving deep into designing an experiment to see osmosis in action.

Lesson notes

(Starter Activity: 10 minutes) Teacher's Action: Use the Think-Pair-Share strategy as suggested in the NaCCA exemplar. Demonstration: Open a bottle of perfume or spray a small amount in one corner of the classroom. (Check for allergies first). Ask learners: "What do you observe after a few minutes?" (The scent spreads). Drop a crystal of potassium permanganate (KMnO₄) into a beaker of still water. Ask learners: "Describe what is happening to the purple crystal and the water." (The purple colour is spreading out). Think-Pair-Share Prompt: "In your pairs, discuss why the perfume scent filled the room and why the purple colour spread through the water without stirring. What is this process called?" Explanation: This process is diffusion. A. Diffusion Definition: Diffusion is the net movement of particles (atoms, molecules, or ions) from a region of their higher concentration to a region of their lower concentration. Key Points: It occurs down a concentration gradient (from high to low). It is a passive process, meaning it does not require energy. It can occur in gases (perfume in air) and liquids (KMnO₄ in water). It does *not* require a membrane. B. Osmosis - The Main Focus

Osmosis is a special type of diffusion that is vital for life. Definition: Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a selectively permeable membrane.

Let's break down the key terms: Water Molecules: Osmosis is specifically about the movement of water, not the solute (like salt or sugar). Selectively Permeable Membrane (or Semi-permeable Membrane): This is a barrier with tiny pores. It is "selective" because it allows small molecules like water to pass through but blocks larger solute molecules like salt or sugar. The cell membrane is a perfect example. Water Potential (Ψ): This is the measure of the tendency of water molecules to move from one area to another. Pure water has the highest water potential (defined as 0). Adding solutes (like salt or sugar) makes the solution more concentrated and *lowers* the water potential (making it negative). Rule: Water always moves from a higher water potential (e.g., 0) to a lower water potential (e.g., -10). Simply put, water moves from a "weaker" solution to a "stronger" solution. C. Types of Solutions and their Effect on Cells

The environment a cell is in determines the direction of osmosis.

Evaluation guide

• Design, model and explain the osmosis process and indicate its application
• to everyday life .
• Group learners according to different abilities and mixed- sex where appropriate.
• Use think -pair-share to discuss diffusion and its application.