| Lesson Plan |
| Grade: |
Date: 25/02/2026 |
| Subject: Biology |
| Lesson Topic: Investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using appropriate controls. |
Learning Objective/s:
- Describe the role of chlorophyll, light and carbon dioxide in photosynthesis.
- Explain how each factor influences the rate of oxygen production measured by leaf‑disc rise.
- Design and conduct a controlled experiment investigating these factors, identifying variables and controls.
- Analyse experimental data to draw conclusions about the necessity of each factor.
- Evaluate sources of error and suggest improvements.
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Materials Needed:
- Fresh spinach leaves (or other green leaves)
- 70 % ethanol for bleaching leaf discs
- Sodium bicarbonate (NaHCO₃) and distilled water
- Transparent 250 mL beakers and rubber bands
- Light source with adjustable intensity (desk lamp)
- Aluminium foil to create darkness
- Timer/stopwatch, forceps and scissors
- Safety goggles and gloves
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Introduction:
Begin with a quick demonstration: place a leaf disc in a bicarbonate solution and ask students what will happen. Recall that photosynthesis requires chlorophyll, light and CO₂, which they have studied previously. Today they will investigate how each of these factors individually affects the rate of photosynthesis using a controlled experiment. Success will be shown by correctly setting up the variables, recording rise times, and interpreting the results.
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Lesson Structure:
- Do‑now (5') – short quiz on photosynthesis basics.
- Mini‑lecture (10') – review the photosynthetic equation, roles of chlorophyll, light and CO₂, and why controls are essential.
- Demonstration & safety briefing (5') – show preparation of leaf discs, bleaching, and apparatus setup.
- Group investigation (25') – students set up three lighting conditions, record rise times for green and bleached discs, repeat trials.
- Data analysis (10') – calculate average rise times, complete the data table, answer analysis questions.
- Whole‑class discussion (5') – share findings, link results to the three factors, identify experimental errors.
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Conclusion:
Summarise that chlorophyll, light and CO₂ are all essential for photosynthesis, as evidenced by the rise‑time results. Students complete an exit ticket stating which factor had the greatest impact and why. For homework, they write a short paragraph predicting how temperature might alter the observed rates.
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