activity 1: (Quick word of caution - this activity involves surgical spirit, which is flammable so must be kept away from fire. It CANNOT be drunk - and you should wash your hands carefully after using it. We suggest a PG rating: no one under 12 should handle the stuff unsupervised.) You will need: 4 onions A large bowl Salt Washing up liquid (cheap brands work best) a funnel coffee filter paper a large plastic cup (transparent if possible) surgical spirit What to do: 1 Finely chop 4 onions and add them to a large bowl. 2 Add 8 teaspoons of salt and 70 mL of washing up liquid. Add 400 mL of warm water to the bowl. 3 Leave for 5 minutes stirring intermittently 4 Put the coffee filter in the funnel and place over a large plastic cup. 5 Gently pour some of the mixture into the funnel and let it drain through. 6 Collect a reasonable amount of liquid (this takes a while so it might be worth leaving it overnight). 7 Take the plastic cup and tilt it. Pour surgical sprit down one side VERY slowly. Keep adding it until you get the same amount of surgical sprit as water. This should take you approximately 3-5 minutes. 8 The surgical sprit will form a layer on top of the water. 9 Place the plastic cup on a table and leave it to settle (away from any heat sources and kids). 10 After 10 minutes you should see a white layer forming between the surgical sprit and onion liquid. You should be able to see white strands here that look like cotton threads. This is the DNA. If you wait longer the DNA should float to the surface. What's going on: DNA is found in the nucleus of every cell that makes up your body, and this applies to all animals and plants. To extract the DNA from your onions, you need to first break the cell walls by chopping up the kiwis. You then have to get through the cell and nuclear membranes. These membranes are made of proteins and fats. Washing up liquid is good at this - in the context of your kitchen sink, it attracts fats from dirty plates when you do the washing up at home - it does the same with the fats in the cell membranes. It pulls out the fats so the membranes collapse. The DNA then floats around in the onion gunk water. The salt binds to the DNA to help us see it later. The filter paper is used to separate the DNA in the liquid from the cell gunk (bits of broken cell walls etc). Finally you add the surgical spirit. This is an alcohol, and DNA can't dissolve in alcohol so it precipitates and you see it in the form of fine white strands. <<Back to Top