Pasteur's Experiments on Spontaneous Generation

in this video, we're going to begin our lesson on louis Pasteur's experiments on spontaneous generation. And so louis Pasteur Was a French chemist from the 1800s who conducted many experiments, including some experiments that demonstrated that microbes are all around us, including in the air that we breathe and so based on stolen Zanny's results, Louis pasture wanted to show that air was actually the source of microbial contamination. And so louis Pasteur designed a simple set of experiments using a specialized type of flask that today we call a swan neck flask because of the resemblance that this flask has to a swan's neck. So if you take a look at an image down below, notice over here on the left, we have an image of louis Pasteur who lived from 18 22 to 18 and conducted the swan neck flask experiments in 59. And so what you see right here is actually the swan neck flask. And notice that the swan neck flask has this long curved tube that leads into the top of the flask and this long curved tube that you see here kind of resembles the curves that you see here in the swans neck, which is why it's called a swan neck flask. And so these swan neck flasks are really just specialized flasks that were designed by louis Pasteur to have a long and curved tube leading into the top of the flash just as what you see down below in this image. Yeah, now the swan neck flasks are really clever in their design because they allowed air to enter into the flask. However, the dust and the microbes that would be in the air would get trapped in the next bend and they would not be able to enter all the way into the flask. And so if we take a look at this image down below, notice that uh dust and air that is found in dust and microbes, I'm sorry that are found in the air they can enter, but they will get trapped in the next bend. They will not be able to make their way back up this uphill portion of the flask, whereas the air itself is able to go all the way up and air is able to get in except the microbes and dust in the air do get trapped over here in the next bend and they can't continue. And so this was a really, really clever design in that fashion, because the vital source or this unknown source that some people claimed was needed for spontaneous generation would be able to reach the broth. But the dust and microbes that were in the air would not be able to reach the broth. And so, using this swan neck flask, louis Pasteur was able to conduct an experiment that ultimately disproved spontaneous generation once and for all, and so we'll be able to talk more about this swan necked flask experiment in our next video. But for now, this year concludes our brief introduction to louis Pasteur's experiments on spontaneous generation, and we'll get to learn more as we move forward. So I'll see you all in our next video.

Louis Pasteur designed swan-necked flasks to:

• A. Keep maggots away from decaying meat.
• B. Pasteurize beer and wine.
• C. Trap microorganisms from the air in the neck of the flask.
• D. Allow dust to reach sterile infusions.

Why did Pasteur design swan-necked flasks in his experiments on spontaneous generation?

• A. The neck excluded oxygen from entering the flask.
• B. The neck stopped microorganisms in the air from contaminating the contents of the flask.
• C. The neck excluded flies and maggots from entering the flask.
• D. The neck served as a handle when heating the flask.
• E. The neck prevented Pasteur from contaminating his sample by sneezing on it.

in this video, we're going to talk more details about louis Pasteur's swan neck experiment. And so pastures experiment actually consisted of the following five steps that notice we have numbered down below in the text and noticed that the numbers in the text actually correspond with the numbers that we have throughout our image. Down below. And so keep that in mind. And so in the very first step of louis, pester, swan neck experiment, the flask is actually going to be filled with a non sterile liquid broth and so by non sterile. What we mean is that there are microbes in that broth. And so notice that in step number one, over here on the far left we have a flask and it is filled with a broth that is non sterile, meaning that there are microbes in that broth. Then in step number two, the swan neck of the swan neck flask is going to be formed using heat. And so if you take a look at step number two in the image down below, notice that the swan neck of the swan neck flask is going to be created and so it's created using heat. As you can see here, there's a flame showing the heat allowing for the bending of the glass and the creation of the swan neck flask. Then in step number three, uh the broth, the liquid broth in the swan neck flask is going to be boiled for a long period of time using an extensive amount of heat. And this long boiling is going to help to create a sterile environment to kill all of the microbes in the bra. And so, taking a look at step number three down below, notice that the liquid broth is going to be boiled for a long period of time, allowing for the liquid broth to become sterile, meaning that all microbes have been killed. Then in step # four, As the flask is allowed to cool from the extensive amounts of heat and boiling, the dust and microbes from the air are actually going to get trapped in the bend of the swan neck flask. And so when we take a look at the image down below. For step number four notice that the dust and microbes that are in the air. They are able to enter originally into the flask, but they get trapped in the bend of the swan neck and they're not able to continue to contaminate and because they get trapped right here, this means that the broth remains sterile and that it is not contaminated. And so as long as this flash stays in its upright position like this, the broth in the flask would remain sterile indefinitely, basically, forever. And so as long as it remains upright, there would be no microbes in the liquid broth. It would remain free of microorganisms, which shows that spontaneous generation is not going to occur does not occur. And so the broth remains sterile as we mentioned already indefinitely, which basically means forever. And so it remains sterile indefinitely, or until step number five of the experiment. And so in step number five, the flask is actually tilted and so tilting the flask or bent, turning it sideways, uh will allow for the mixing of the trapped microbes with the sterile broth and once the microbes have been mixed with the sterile broth that allows for microbial growth to be observed. And so if you take a look down here at step number five, notice that the swan neck flask is tilted to allow the liquid broth to mix with the microbes from the air and that mixing of the broth with the microbes allows for microbial growth to be observed. And so over here you can see that the microbes are present and the liquid after tilting the flask and mixing it. And so what this shows is that spontaneous generation of microbes is not going to happen and that microbial growth only comes from pre existing microbes. And so these are the conclusions that louis Pasteur was able to come up with number one microorganisms cannot spontaneously generate. They do not spontaneously generate. Otherwise, we would have seen spontaneous generation of microbes when the flask is upright. But in the second conclusion that he was able to make is that life requires life to form, that he would only see my significant microbial growth when the microbes that were trapped were mixed into the bra. And so this supported the theory of biogenesis. That life new life only comes from pre existing life. And so this year concludes our introduction to louis pastures, swan neck experiment and how it's supported biogenesis and it disproved spontaneous generation. And so we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Which of the following is not a valid conclusion and/or outcome of Pasteur's experiment refuting the theory of spontaneous generation?

• A. That microorganisms are present everywhere, even in the air.
• B. The development of aseptic techniques when working with microbial cultures.
• C. Microorganisms can cause disease.
• D. Living cells can only develop from pre-existing cells.