What it shows
Plants, soil and water in a closed bottle recycle water through transpiration and condensation. It models how the Earth’s own cycles work.
The science
Plants take in water through roots and release vapour from leaves (transpiration). The vapour condenses on the cool wall and trickles back to the soil, so water is reused. Plants use carbon dioxide and sunlight to make food, giving out oxygen. Soil organisms break down dead leaves and return nutrients. Too much water causes mould, so balance matters.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A large clear plastic bottle or a glass jar with lid
- Small stones and charcoal pieces
- Garden soil
- Two or three small plants such as moss or money plant cuttings
- A spoon and a spray bottle of water
- Tape
Safety
For this project: An adult must cut the bottle. Wash hands after handling soil.
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.
An adult cuts the bottle across at the shoulder so a lid can be fitted back.
Put 2 cm of small stones at the bottom for drainage.
Add a layer of charcoal and then 5 cm of soil.
Plant the small plants and press the soil around the roots.
Mist lightly with water and close the bottle with tape.
Place in bright light but not in direct hot sun.
Observe for four weeks, noting condensation and growth.
Open and mist only if the soil is dry.
What you should see
Water droplets form on the walls in the morning and fall back at night, and the plants stay green for weeks without watering.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is transpiration?
Loss of water vapour from leaves.
2Why do droplets form on the wall?
Vapour condenses on the cooler surface.
3Why not keep it in direct hot sun?
It would overheat and cook the plants.
4What do the stones do?
They give extra room for drainage.
Take it further
Keep a second open bottle and compare how much water each needs.
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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