What it shows
A sealed jar with soil and plants keeps its own small water cycle. Water evaporates from the soil and leaves, condenses on the glass and runs back, while plants and soil life swap oxygen and carbon dioxide.
The science
Plants take in carbon dioxide and make food and oxygen in light, and they, with the soil microbes, also respire and give off carbon dioxide. Water evaporates from the soil and transpires from the leaves, then condenses on the cooler walls and trickles back, so the same water circulates. Minerals recycle as dead leaves decay and feed the plants. The garden works as a small ecosystem, though a few of these gardens still need a little care, and any mould is removed.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large clear glass jar or a 2 litre plastic bottle with a wide cut opening, with a lid or cling film
- A handful of small pebbles
- Crushed charcoal (a few pieces)
- Garden soil or potting mix
- Two or three small plants, such as a money plant cutting, a small fern or moss
- A spoon, a long stick to place plants
- A spray bottle of water
Safety
For this project: An adult must cut the bottle. Wash your hands after handling soil. Do not place the jar in strong direct sun, where it can overheat and cook the plants.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Spread a 2 cm layer of pebbles at the bottom of the clean jar for drainage.
Add a sprinkle of crushed charcoal, which helps keep the water fresh.
Add about 5 cm of soil on top and press it gently.
Make small holes with the stick and plant the small plants, firming the soil around the roots.
Spray the soil lightly so it is damp but not wet, and wipe the glass clean.
Close the jar with the lid or cling film and place it in bright light but out of direct sun.
Watch daily for mist on the glass, droplets running down and any changes in the plants, and write them in a diary.
Open the jar only if the glass is always dripping wet (too wet) or very dry, and remove any mould you see with a clean spoon.
What you should see
Mist forms on the glass in the morning and clears as the day warms, droplets run back to the soil, and the plants stay green for weeks without extra water.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Where does the mist on the glass come from?
Water that evaporated from the soil and leaves and then condensed on the cooler glass.
2How do the plants get carbon dioxide inside a sealed jar?
From their own respiration and from the soil microbes that decay dead matter.
3Why not place it in direct hot sun?
The air inside would get too hot and the plants could die.
4Why is the jar a small ecosystem?
It contains producers, decomposers, water, air and soil that cycle materials.
Take it further
Make a second jar without charcoal or pebbles and compare how the plants fare after a month.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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