| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: investigate the effects of immersing plant tissues in solutions of different water potentials, using the results to estimate the water potential of the tissues |
Learning Objective/s:
- Describe the concepts of water potential, solute potential and pressure potential and how they govern water movement in plant cells.
- Explain how osmosis and plasmolysis are observed when plant tissues are placed in solutions of differing water potential.
- Calculate percentage mass change, construct a % Δm vs. sucrose concentration graph, and determine the isotonic point.
- Convert the isotonic sucrose concentration to solute potential and estimate the water potential of the plant tissue.
- Interpret experimental results to assess whether water moved into or out of the tissue.
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Materials Needed:
- Fresh potato tuber or onion epidermal strips
- Sucrose solutions (0 %, 0.2 %, 0.4 %, 0.6 %, 0.8 %, 1.0 % w/v)
- Distilled water
- Electronic balance (±0.01 g)
- Labelled test tubes or beakers
- Timer/stopwatch
- Ruler (for epidermal strip length)
- Lab coat, safety glasses, and a sharp knife
- Worksheet for data recording and graph paper
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Introduction:
Begin with a quick question: “What would happen to a piece of potato if you placed it in a very salty solution?” Students recall prior learning about osmosis and water potential. Explain that today they will use quantitative measurements to estimate the water potential of plant tissue, and they will know they have succeeded when they can identify the isotonic concentration and calculate Ψ for the tissue.
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Lesson Structure:
- Do‑now (5'): Students answer a short prompt on water potential and osmosis.
- Mini‑lecture (10'): Review key formulas (Ψ = Ψs + Ψp) and concepts (plasmolysis, turgor).
- Demonstration (5'): Teacher shows how to prepare sucrose solutions and cut uniform tissue pieces.
- Practical investigation (20'): Groups place six tissue pieces in the labelled solutions, record initial masses, and incubate for 30 min.
- Data analysis (10'): Students blot samples, record final masses, calculate % Δm, and plot the graph to find the isotonic point.
- Calculation (5'): Using the isotonic concentration, compute solute potential and estimate tissue water potential.
- Check for understanding (5'): Whole‑class discussion of results and extension questions.
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Conclusion:
Summarise how the graph’s zero‑change point reveals the tissue’s water potential and why this matters for plant physiology. Students complete an exit ticket stating the estimated Ψ value and one factor that could affect accuracy. For homework, assign a brief report comparing results if NaCl were used instead of sucrose.
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