| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: explain how environmental factors can act as stabilising, disruptive and directional forces of natural selection |
Learning Objective/s:
- Describe how temperature, food availability, predation pressure and habitat structure generate stabilising, disruptive, or directional selection pressures.
- Explain the effect of each selection type on phenotypic variation and on the population mean.
- Compare natural and artificial selection using the three selection mechanisms.
- Calculate a selection differential to assess the strength of selection in a given population.
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Materials Needed:
- Projector and screen
- PowerPoint/Google Slides with diagrams of selection curves
- Printed handouts containing case‑study excerpts and the selection‑differential worksheet
- Whiteboard and markers
- Clicker or online quiz platform for the exit ticket
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Introduction:
Start with a quick poll: “Which local animal traits have you noticed changing in recent years?” Connect these observations to prior knowledge of natural selection. Explain that by the end of the lesson students will be able to identify and describe stabilising, disruptive and directional selection driven by environmental factors.
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Lesson Structure:
- Do‑now (5'): Students list recent environmental changes and hypothesise possible trait responses.
- Mini‑lecture (10'): Definitions of natural & artificial selection; illustrate stabilising, disruptive, directional curves.
- Guided case‑study analysis (15'): Small groups examine three examples (medium‑sized birds, niche‑divided fish, beetles in warming climate) and label the selection type.
- Whole‑class discussion (10'): Compare natural vs artificial selection examples; clarify misconceptions.
- Quantitative activity (10'): Using provided data, calculate the selection differential (S) and interpret its magnitude.
- Exit ticket (5'): Each student writes one sentence summarising each selection type and its environmental trigger.
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Conclusion:
Recap the three selection mechanisms and how specific environmental factors drive them. Collect exit tickets to gauge understanding, and assign homework: read the textbook section on selection and prepare a short real‑world example of each selection type for the next lesson.
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