Bubbling Plants: Quantifying Photosynthesis

Students place Elodea in baking-soda water and count gas bubbles produced in low light and bright light for fixed time intervals. Comparing bubble counts provides an indirect, simple measure of photosynthesis under different light intensities.

1. Fill a 500 mL beaker with aged tap water and dissolve a small pinch of baking soda; stir until clear.
2. Arrange 18–24 inches of Elodea so leaves are exposed (loop around the beaker bottom); tie loosely and weight so it stays submerged about 1–2 inches.
3. Set the beaker in dim classroom light; start a 5 minute timer.
4. Two observers watch for rising bubbles while a recorder tallies each bubble that reaches the surface.
5. After 5 minutes, position a desk lamp a few inches above the beaker to provide bright, direct light.
6. Reset the timer and count bubbles again for 5 minutes under high light.
7. Record both counts, then compare results across groups; compute mean or median if pooling class data.
8. Make a simple bar graph showing bubble counts for low versus high light and interpret which condition had more photosynthesis.

Bubbling Plants Experiment to Quantify Photosynthesis - TeachEngineering:

Photosynthesis in Elodea - John Hindmarsh:

📄 Bubbling Plants Experiment to Quantify Photosynthesis - ncwit.org: [https://www.teachengineering.org/activities/view/duk_photo_mary_act]]

• Test different distances from the lamp to change light intensity.
• Cover the beaker with colored film (red, blue, green) to compare light colors.
• Add more or less baking soda to see if carbon dioxide availability matters.

• Keep hot bulbs several inches from plastic and plants.
• Handle glassware carefully on a stable surface to avoid spills and breaks.
• Do not ingest any materials; wash hands after the activity.
• Supervise electrical cords and water to prevent shock hazards; keep plugs and outlets dry.

• Why do bubbles indicate photosynthesis? (They are mostly oxygen released during photosynthesis.)
• Why add baking soda to the water? (It supplies dissolved carbon dioxide for photosynthesis.)
• How should bubble counts change with more light? (Counts usually increase because light powers the reactions.)
• What is a fair test when comparing low and high light? (Keep all other variables the same: plant amount, water, time, and distance except for the light condition.)
• Is bubble counting a direct or indirect measure of photosynthesis? (Indirect; it infers photosynthesis rate from visible gas production.)