Science Projects with an Onion
Just as there are many layers to an onion, so there are several very different science projects that can revolve around this versatile vegetable. Onions release a chemical that makes humans cry, but that actually protects the onion plant from germs and insects. A simple science project can test the popular methods for preventing or stopping humans from crying while chopping onions. The onion also lends itself to DNA extraction in a more complex science experiment.
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The Crying Experiment
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It's no secret that chopping an onion often leads to tears. When the onion is cut, it releases an enzyme known as allinase and a sulfur compound. They form a volatile chemical that gets into our eyes and reacts with the water in them. There are a variety of remedies on how to help stop the tears associated with onion chopping. This experiment allows the student to scientifically evaluate the effectiveness of the remedies. The common remedies include placing the onion in the freezer for fifteen minutes before chopping. Another is to work a slice of bread onto your knife so that it absorbs the fumes that cause tears. The third is to light a candle in the work area prior to chopping the onion. The candle is supposed to burn off the gasses produced by the onion. Students can put these hypotheses to the test and determine through comparison if any are effective and which one works best. Volunteers who are willing to cry several times will be needed.
Onion DNA
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This science project teaches students how to separate onion DNA from other cellular components without interfering with its sequence or structure. The experiment involves chopping up an onion and placing the pieces into a measuring cup. Then prepare two sets of solutions that contain a tablespoon of shampoo and a quarter of a teaspoon of salt. Place each solution in a beaker and add distilled water. Pour the solution over the chopped onion. This causes the membrane of the cells to break down. The cup with the onion is placed into a hot water bath for 10 minutes to allow phospholipids to soften. This is followed by an ice water bath for five minutes. The mixture is then filtered and the onion solution is poured into a test tube. Cold alcohol is added and the DNA will precipitate into the alcohol layer. There should be sufficient DNA to spool onto a glass rod.
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Decomposition
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This science project teaches students about the nature of decomposition. It is not for the squeamish, as onions are particularly smelly. Have students cut an onion in half and place one half in a clear container that is then placed in a sunny, warm area. Put the other half of the onion in a clear container that is stored in a dark place. Students can then write up their observations over time of what is happening to each onion half. They should compare the changes and make a note of them. A chart can be drawn up showing the factors that facilitate decomposition. Brave students can examine the fungi and mold that grows on the onions with a magnifying glass.
Onion Lifecycle
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Onions are members of the allium family and are biennials, which means that they bloom in the second year. Have students create a diary of an onion in which they document, from the onion's perspective, the way that they grow and the different ways they can be cultivated. Remind students that while this is a science project and they should provide accurate facts about onions, they can also be creative and imaginative. Inspire them to write a poem about the multiple layers of an onion and then decide on an ending for their onion's story. The onion can end up in a delicious stew feeding the poor or in a compost heap after it is destroyed by burrowing maggots.
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References
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