Measuring Photosynthesis With Pondweed and Light
Photosynthesis is the process that keeps our planet alive — but how do students measure it in the classroom? A classic experiment with pondweed brings the equation to life:
🧪 The Classic Experiment
We place a piece of pondweed (often Elodea or Cabomba) in water and expose it to light. As photosynthesis occurs, oxygen bubbles are released.
Students can:
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Count the number of bubbles per minute.
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Measure the volume of oxygen collected in a syringe or gas tube as in the photo.
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Compare results under different conditions by recording the light levels.
💡 The Effect of Light
By moving the lamp closer or further from the pondweed, students test how light intensity affects the rate of photosynthesis. Results are usually plotted as a classic inverse square law curve — rapid increase at first, then levelling off as another factor (like CO₂ or temperature) becomes limiting.
📊 Extending with Sensors
With PASCO CO₂ or O₂ sensors, students can measure gas concentration changes directly, getting real-time graphs of photosynthesis vs respiration. This makes the experiment more accurate and links perfectly to GCSE and A-Level exam skills.
🎓 Why It Works in Teaching
This experiment:
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Turns a textbook process into something visual and measurable.
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Reinforces variables and fair testing.
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Demonstrates limiting factors in action.
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Builds a bridge between theory, data handling, and real-life plant biology.
Students leave not just knowing the photosynthesis equation, but having seen oxygen produced before their eyes.
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