Sophie Duncan uses a bunch of carrots to tap into osmosis

18th June 2004 at 01:00
Carrots provide an interesting resource for exploring taproots. Try these experiments to find out how taproots work.

Place a carrot in a jar containing water coloured with food dye. Place it in a sunny position on the windowsill and leave it for at least 24 hours.

Observe the carrot - some of the smaller secondary roots may have started to grow. Cut the carrot in half lengthways and observe how the water has moved through the root.

Take two more carrots. Cut the first in half lengthways, and the second in half widthways.

Make observations of what the carrot looks like, and then place each half into a jar of water. Leave them in a sunny position for 24 hours, and then observe. Secondary roots will have started to grow. Make a note of where the new roots have grown.

Finally, use a small knife to make a hole about 1cm deep in the middle section of a carrot where the leaves would normally be attached. Push a short piece of drinking straw into this hole, and seal around it with candle wax.

Cut the tip off the other end and place the carrot into a jar of coloured water.

Place this in a sunny position, and leave it for a couple of days, making daily observations.

The water will appear in the straw; it moves through the carrot by osmosis, the process by which water molecules can pass through semipermeable membranes from an area of low concentration to one of high concentration.

You can observe osmosis if you have an old carrot that is quite bendy.

Place it in a glass of water, and after a few hours it will be restored.

Sophie Duncan is project manager for science at the BBC

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