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I realise that the best way to prove the existence of germs or single-celled organisms is by looking at them through a microscope. But I don't have a microscope at my home, how can I design an experiment in a normal house environment to show the existence of germs (or other single-celled organisms) without spending too much money?

By "house environment" I mean that I have access to normal stores and the internet. If it's something that can be bought in a "normal" store or on-line without getting me into trouble, and doesn't cost a lot then I can have access to it. I don't have access to lab grade equipment or conditions, so no sterile rooms or special growth environment.


I thought about the following experiment, inspired by the mythbusters pyramid power episode. In the episode they cut an apple in half and put one half under a pyramid and the other not under a pyramid. In the first attempt one of the halfs rotted quicker than the other, they concluded that it happened because the saw they used to cut the apples wasn't sterile.

So I thought about taking 3 apples, contaminating a knife (by rubbing human saliva on it). Cutting one apple with the contaminated knife, one apple with a sterile knife (using rubbing alcohol to sterilize it) and one apple by a knife that has 1 contaminated side and one sterile, which is a contaminated knife, that had only 1 side sterilized with rubbing alcohol. Then leaving the 6 halves in separated sealed containers (some tupperware) for a few days and then looking examining the rott. The expected result is that the "contaminated apple" will have a lot of rot on both halves, the "sterile" apple will have no (or close to no) rot, and the half and half apple will have one rotten side and one not rotten side, and the sides will coincide to the contaminated/sterile sides of the knife touching them.

Will this experiment work?

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Do you have access to growth media (agar plates)? –  Chris Jan 29 at 11:42
    
I have access to normal stores and the internet. If it's something that can be bought in a "normal" store or on-line without getting me to trouble, then I have access to it. –  Ilya Melamed Jan 29 at 12:07
    
Is proving existence of fungi relevant ? If so, you could wet a bread with water and keep it in a hot and humid place. You will see moulds growing after 2-3 days. –  biogirl Jan 29 at 14:09
    
@biogirllajja, what is the control group? how do I prove that those are microorganism and not just a property of the bread? –  Ilya Melamed Jan 29 at 14:16
    
@IlyaMelamed You could keep the bread in a refrigerator where the fungi will not grow. –  biogirl Jan 29 at 14:18

2 Answers 2

You could use Jell-O for growing bacteria if you don't have access to agar ! (I have never tried this but I think it should be possible because the gelatin in Jell-O is like agar.)

You should first sterilize a small knife on a gas stove or with alcohol and then gently rub it on any surface (where you think bacteria are likely to be found ) and then rub it on Jell-O taken in a dish. You should then place it in an environment similar to the one from where you isolated the bacteria. After one or 2 days the bacteria should grow.

For control : You could simply put a plate of Jell-O in the same place but without inoculation of bacteria.

Disclaimer : I am not a microbiologist and I am not sure this would work but you could give it a try as it will not be really expensive :)

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Agar is easily available online (~5 euros for 100 g on eBay). For how to make the plates, and a sample experiment see here –  nico Jan 29 at 15:36

I see no reason to restrict yourself to jello or buy agar (its not expensive tho).

Every piece of rotting leftover in the fridge pretty much proves that bacteria and fungi exist....

You can always sterilize any food by boiling it (like jello). A pressure cooker is better than just boiling it. You will have to boil the dishes you are using too.

Then expose one dish to something that contains germs and compare it to a sealed sterile container of the food. Breathe on it or put your finger in it - that should be enough.

Seal the exposed container up good after exposure tho - it can get messy!

Fruit and even coffee will grow the junk you want pretty quick. Leave it at room temperature for faster results.

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Good point. We always tend to think to complicated. The above example with the bread works as well.... –  Chris Jan 29 at 18:23

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