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:

$$6CO₂ + 6H₂O \; \xrightarrow{light} \; C₆H₁₂O₆ + 6O₂$$

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🧪 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:

• Count the number of bubbles per minute.

• Measure the volume of oxygen collected in a syringe or gas tube as in the photo.

• Compare results under different conditions by recording the light levels.

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💡 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.

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📊 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.

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🎓 Why It Works in Teaching

This experiment:

• Turns a textbook process into something visual and measurable.

• Reinforces variables and fair testing.

• Demonstrates limiting factors in action.

• 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.