What it shows
An onion bulb can grow roots when it touches water. We can watch the roots grow day by day and measure them.
The science
A bulb is a short stem with fleshy leaves that store food. The bottom of the onion has a flat plate from which roots grow when it gets water. Roots take in water and hold the plant. The stored food in the bulb is used for new growth.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- One small onion (free from the kitchen)
- A glass jar with a narrow mouth
- Water
- Three toothpicks
- A ruler
- A notebook
Safety
For this project: An adult must push the toothpicks into the onion and watch that children do not poke themselves.
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.
Fill the jar with water to the brim.
Push three toothpicks into the sides of the onion, a little above the bottom.
Place the onion on top of the jar so that only the bottom touches the water.
Put it in a sunny place and mark the water level on the jar.
Top up the water every day.
On day three look for white roots and draw them.
Measure the longest root each day with a ruler.
After a week, note whether a green shoot has also come out on top.
What you should see
White roots grow downward into the water and by one week are 3 to 6 cm long. A green shoot may grow from the top.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which part of the onion makes roots?
The bottom plate of the bulb.
2What do roots do?
They take in water and hold the plant.
3Why does an onion have food stored?
To help the new plant grow.
4Why did we top up the water?
The roots need to stay in water.
Take it further
Keep two onions, one in sun and one in shade, and compare root length.
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
Science projects
Easy Science Projects for Class 1 to 5
Simple, safe projects young children can make with a little help
Science projects
Biology Models Guide
Make the heart, lungs, kidney, eye, cell and more, and explain them well