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Can plants and animals live for weeks in a sealed jar? Where does their oxygen come from?
Ecosystem Balance lab · Last updated: 16 October 2026
Can plants and animals survive for weeks in a sealed jar? In this 3D lab, you watch oxygen, carbon dioxide and nutrients move between plants, animals and decomposers in a closed world. It shows how living things depend on each other, and why only sunlight needs to come in from outside.
What you'll discover
- Plants release oxygen when they photosynthesise in light, and both plants and animals use it to respire.
- Animals and decomposers return carbon dioxide and nutrients that plants need to keep growing.
- Matter is recycled inside the jar, but energy has to keep arriving as light.
The science in plain words
An ecosystem is a community of living things together with their non-living surroundings, such as air, water, soil and light. A sealed jar with water plants, a few snails and some microbes is a tiny ecosystem, and it shows clearly how its parts depend on one another.
In light, plants photosynthesise: they take in carbon dioxide and water and use the energy of sunlight to make sugar, releasing oxygen as a by-product. That is where the oxygen in the jar comes from. Plants, animals and microbes all respire, day and night, using oxygen to release energy from food and giving out carbon dioxide. When the light is bright, plants make more oxygen than everything uses, and in the dark the oxygen level slowly falls.
Decomposers such as bacteria and fungi break down waste and dead material and return nutrients like nitrogen and phosphorus to the water, where plants can absorb them again. So the atoms inside the jar go round and round in cycles. Energy is different: it flows in as light and leaves as heat, so it must be constantly topped up. If the balance is upset, for example with too many animals or too little light, oxygen can run out and the jar ecosystem collapses.
Where it fits
Common questions
How can a plant survive in a sealed jar?
In light, the plant makes its own food and oxygen by photosynthesis, using carbon dioxide and water already in the jar. Microbes break down dead leaves and return nutrients to the soil or water. As long as it gets light and has some moisture, the plant can keep recycling what is inside.
What is an ecosystem?
An ecosystem is all the living things in an area, such as plants, animals, fungi and bacteria, together with the non-living things they depend on, like water, air, soil and sunlight. A pond, a forest and even a sealed jar can each be an ecosystem.
Where does the oxygen we breathe come from?
Nearly all the oxygen in the air comes from photosynthesis by plants, algae and certain bacteria. Tiny ocean organisms called phytoplankton make a large share of it. They use sunlight to turn carbon dioxide and water into sugar, releasing oxygen as a by-product.
Related labs
- Photosynthesis: Plants make their food from light, water and carbon dioxide. Can we see it happening?
- Food Web: Who eats whom in a meadow? Take one species away and see what happens to the rest.
- Carbon Cycle: When we burn fuel, where does the carbon go? And how much of it stays in the air?
See all biology labs or every Taz science lab.
Try it yourself
The Ecosystem Balance lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.