help for prac (1 Viewer)

[jellybean_girl]

i need help to plan the prac of pasteur do perform it in class if anybody could help me that would be great or if you know any sites please that would be great i have already lokked at hsc online

 

[babydoll_]

Pasteur was attempting to disprove the theory of spontaneous generation with his experiment.

In this practical, he used broth which had been sterilised by boiling. Broth was placed into two flasks - one with a 'swan neck' (bent into a S-shape), and one directly open to the air. Air could enter the flasks, but dust and pathogens would get caught in the 'swan neck' of the first flask, whereas pathogens would enter the other flask directly and cause spoilage.

This site is very detailed:
http://www.cat.cc.md.us/~kdalton/Bio110/lab/report.htm

 

[untamedanimal]

Do you have to do the actual experiment or any experiment that would model his one?

 

[jellybean_girl]

we have 2 do an experiment like Pasteur's but a way that we can conduct in class! Its in the dot points

 

[MaryTylerMoore]

To conduct this experiment in class you will need two connical flasks, two rubber stoppers, two glass tubing in an S shape (commonly referred to as swan-neck) tubing. You should have some chicken or beef broth (like chicken or beef soup), but make sure it doesn't have too much salt or the bacteria won't be able to grow in it as water would flow out of them by osmosis.

If you don't have an swan-neck tube, you may need to make it yourself (but very carefully). You need to heat the glass in a Bunsen burner flame and bend it and allow it to cool. This can get VERY HOT and it could snap very easily. Hopefully, the teacher could do this for you.

Prepare your broth and pour equal amounts into both connical flasks. If you make your own broth at home, there will be solid fat at the top so you might want to first of all make the soup, put it in the fridge, pick off the fat and then let it become liquid again. Put on clean rubber stoppers, and then insert the tubing to ensure they both fit snugly. You might want to use a membrane perhaps to prevent the air coming in if the tube/stopper don't fit snugly.

Allow the contents of both flasks to boil for 15 minutes and then let them cool a bit. Break off one of the swan-necked tubes leaving a vertical/straight piece of tubing and keep it in a place out of direct sunlight.

In this experiment, Louis Pasteur was trying to show that it wasn't air that caused spoilage, but the particles in air which he termed 'germs'. This disproved spontaneous generation - also known as abiogenisis.

 

[jellybean_girl]

Thanks heaps that was a lot a help especially the glass bending part

 

[MaryTylerMoore]

I just want to add that instead of using a straight tube for both, you need to use a bent tube for both that you boil both with the bent tube for 15 minutes, but break off the bent tube once a bit cool to leave a straight section of tubing behind.

My teacher says a water lock should remain - that is, after boiling there should be a trap of water so no air can enter, but I believe the purpose was to show that it was not air that caused the spoilage, but the dust in it. He maintains that the water prevents any air and dirt from entering. I drew the diagram with the water lock as that is what it looked like, but the text book does not show a water lock and states that it was meant to allow air to enter.

 

[F.I.F.I]

hi guys does any one use the prac mannual? if u do can u please help out with experiment 7.3

 

[jellybean_girl]

thanks heaps guyz i've just done the experiment lets hope i get good results