A-maze-ing onions

You will need:

An onion (ideally already sprouting)
A shoe box
Another spare cardboard box
Strong scissors
Sticky tape

What to do:

First build a maze for your onion!
Use your spare cardboard box to cut rectangles about the same size as the smaller side of the shoe box. These will be the dividers inside your maze. You need at least two but you could make more if you like.
For each divider, cut a ‘window’ in the cardboard about 3 cm square. It will make the maze more interesting if they are in different positions on each divider.
Cut an ‘exit’ door for the onion shoot at one end of the shoe box.
Put the onion at the other end of the shoe box..
Fit the dividers into the box, spacing them out between the onion and the exit. Try to put them in so the onion will have to change direction to get through each hole.
Try to find a sunny place to leave it (so the sun can shine on the exit) but where it won’t be disturbed.
Leave for about 3 weeks and then check to see how it’s getting on.

What’s going on?

The sprouts on your onion should have started to find their way out of the maze. They are growing towards the light coming through the exit. Biologists call this phototropism. You might have noticed this already with indoor plants. They grow towards the light, and can get very lopsided unless you turn their pots round occasionally.

So how does the onion ‘know’ where the light is, and how does it grow towards it? The tips of plant shoots contain a growth hormone called an auxin, which makes the shoot grow faster. But light destroys the auxin, so it only works on the side that doesn’t have any light. The side without any light grows longer and the shoot ends up bending towards the light.

You might have also noticed that plants without much light grow long and spindly. This is because there is lots of auxin in the plant and it grows fast – but the plant won’t be very healthy because it needs light to make food for itself by photosynthesis.

More ideas

Try seeing if a sprouting potato can find its way through the maze. Have a race between the potato and the onion to see which shoots grow quicker.

You could grow plants from identical seeds, one in the dark and one in the light to compare them. Look especially at the colour of the leaves. Think of ways to test whether the auxin is only in the tips of the shoots or all along the shoots.