| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: Describe osmosis as the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane. |
Learning Objective/s:
- Describe osmosis as the net movement of water from higher to lower water potential across a selectively permeable membrane.
- Explain the factors that influence the rate and direction of osmosis (solute concentration, pressure, temperature, membrane properties).
- Interpret hypo‑, iso‑, and hypertonic situations and predict cellular responses.
- Apply the water‑potential equation (ψ = ψₛ + ψₚ) to solve simple problems.
- Conduct a basic potato osmosis experiment and analyse the observed mass changes.
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Materials Needed:
- Projector and screen
- Whiteboard and markers
- Handout with key definitions, equations and diagrams
- Potato pieces, beakers, distilled water, 0.5 % NaCl solution, 5 % NaCl solution
- Digital balance
- Timer/stopwatch
- Worksheet with practice questions
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Introduction:
Begin with a quick demonstration: show a dry sponge absorbing water, prompting students to consider why water moves spontaneously. Recall prior learning about diffusion and ask how water movement differs when a membrane restricts solutes. Explain that by the end of the lesson they will be able to describe osmosis, predict its direction in different solutions, and justify the underlying water‑potential concept.
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Lesson Structure:
- Do‑now (5') – students answer a short question on water potential on the board.
- Mini‑lecture (10') – present definitions, water‑potential equation, and factors influencing osmosis using slides.
- Interactive modelling (8') – diagram of a semi‑permeable membrane; students label water‑movement directions for hypo‑, iso‑, and hypertonic conditions.
- Laboratory demonstration (15') – conduct the potato experiment; students record initial masses and set timers.
- Data analysis & discussion (10') – groups calculate mass changes, relate them to water potential, and answer guided questions.
- Practice questions (7') – individual work on the worksheet while teacher circulates.
- Quick check (5') – exit ticket: one sentence describing why a cell shrinks in a hypertonic solution.
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Conclusion:
Summarise that osmosis drives water movement from higher to lower water potential and is governed by solute concentration, pressure and membrane properties. Students complete an exit ticket stating the cellular outcome for each osmotic condition, reinforcing the key concepts. Assign homework to solve two water‑potential calculations and write a brief paragraph on the role of osmosis in kidney function.
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