• Question: How is the chemical formed in an onion ? (the one that makes water pur out of your eyes)

    Asked by Deeps 2005 to Chris, Hayley, Jimi, Omur on 16 Mar 2016. This question was also asked by Resh@science.
    • Photo: Hayley Moulding

      Hayley Moulding answered on 16 Mar 2016:

      There is a chemical called syn-prpanethial-S-oxide (that is a really long word) that caused you to cry when you cut the centre of the onion! When you cut through the onion, an enzyme called ‘allinase’ causes the break down of the chemical and makes your eyes irritate and cry!!!! Making anyone cry! Sometimes I wear contact lenses or wear my scientific goggles or swimming goggles. They help to not cry!

    • Photo: Jimi Wills

      Jimi Wills answered on 16 Mar 2016:

      The chemical make you cry if it gets up your nose too, so I always breathe through my mouth when I’m chopping onions.

      To expand on Hayley’s answer, an enzyme is a type of protein that helps a chemical reaction to happen. Proteins are made according to the information in genes. Your DNA contains genes, and you get half from your mum and half from your dad. You mostly have two copied of each gene, one copy from each parent. Each gene has the information for one type of protein (usually). So onions have a gene that make the allinase protein, that then converts the chemical.

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