Sealed Jar Mesocosm – Ecosystem Stability Lab
BiologyEcology & EnvironmentAges 17–18Virtual lab
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Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Ecology & Environment
Set up a sealed jar with water, plants, snails and pond mud, choose the hours of light and the added nitrate, and follow dissolved oxygen, CO₂ on a hydrogencarbonate indicator and the populations week by week. Judge which designs stay stable. A second tab uses indicator tubes to find the light at which photosynthesis balances respiration.
Lesson: Mesocosms and ecosystem stability: balance of photosynthesis and respiration, decomposers and nutrient cycling in a closed system
What it shows
A mesocosm is a small ecosystem kept under controlled conditions. In a sealed jar, light enters and heat leaves, but no matter crosses the glass, so the jar stays alive only if it recycles its carbon, oxygen and nutrients. This lab follows a litre of water with water plants, snails, algae and decomposers over the weeks. Producers must fix as much carbon as the whole community respires, and decomposers must return nutrients. Too little light, too many snails, no decomposers or too much nitrate each upset the balance in a different way. The rates are estimates.
How to use
On Sealed jar, set Light, Plant sprigs, Snails, Pond mud, Added nitrate and Length, then press Seal and run. Watch the graph, and switch it between Oxygen and pH, Populations and Oxygen budget. A row is added each week and one for each finished jar. On Indicator tubes, set Light and press Incubate 24 h, then repeat at other light levels. Answer the check questions from your results.
Parameters you can change
- Experiment Sealed jar, Indicator tubes
- Light 0–24 h/day
- Plant sprigs 0–6
- Snails 0–10
- Spoons of pond mud 0–3
- Added nitrate (as N) 0–10 mg/L
- Length 8–24 weeks
- Graph Oxygen and pH, Populations, Oxygen budget
- Light on the tubes 0–24 h/day
Questions to explore
- What happens first to oxygen, pH and the snails in a jar kept in the dark, and in what order?
- How does a jar with no pond mud change over 12 weeks, even though oxygen stays high?
- How much added nitrate does it take for algae to overtake the plants, and what then happens to the oxygen?
