investigate the rate of photosynthesis in pondweed by measuring oxygen production.

To study the effect of light intensity on the rate of photosynthesis in pondweed by measuring the volume of oxygen released.

Materials

  • Beaker

  • Funnel

  • Graduated cylinder

  • Sodium hydrogen carbonate solution (source of CO₂) technically baking soda

  • Pondweed (e.g., Elodea or Cabomba)

  • Lamp (light source)

  • Ruler

Method

  1. Setup the Apparatus:

    • Place the pondweed in a beaker filled with sodium hydrogen carbonate solution. The solution ensures a constant supply of CO₂ for photosynthesis.

    • Position the funnel over the pondweed with the stem of the funnel submerged in the solution.

    • Fill the graduated cylinder with water and invert it over the funnel stem to collect oxygen gas.

  2. Position the Lamp:

    • Place the lamp at a fixed distance from the beaker as the light source.

  3. Start the Experiment:

    • Turn on the lamp and allow photosynthesis to occur. Oxygen bubbles released by the pondweed will collect in the graduated cylinder.

  4. Measure the Oxygen Volume:

    • Record the volume of oxygen collected in the graduated cylinder over a fixed time interval (e.g., 5 minutes).

  5. Vary Light Intensity:

    • Change the distance of the lamp from the beaker to vary light intensity (e.g., 10 cm, 20 cm, 30 cm).

    • Repeat the measurement for each distance.

  6. Control Variables:

    • Keep the temperature, CO₂ concentration, and type of pondweed constant.

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Observations

  • Closer lamp distances (higher light intensity) generally increase the rate of bubble formation and oxygen collection, indicating higher photosynthetic activity.

Conclusion

The experiment demonstrates that light intensity affects the rate of photosynthesis. As light intensity increases, the photosynthetic rate typically increases up to a point.

This setup is simple and effective for exploring photosynthesis and can be extended to investigate other factors like temperature or CO₂ concentration.

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