Pasteurs ExperimentScience Practical Report

Venkat Aluru - DATE \@ "d MMMM y" 19 May 2015SCIENCE PRACTICAL- VENKAT ALURU PAGE 2

Aim:

To disapprove the theory of spontaneous generation by using Louis Pasteurs experiment. Spontaneous generation was once a theory that living things were created from non living things for example, fish from the mud in previously dried lakes.

Hypothesis:

The experiment is to disapprove the theory of spontaneous generation therefore it would logical to say that spontaneous generation doesnt occur as will be shown by the flask which is exposed to the air while the conical flask not exposed to the air will be sterile.

Materials:

Conical Flask With StopperConical Flask Exposed To AirHot PlateNutrient Broth

Method:

1. Pour 150ml worth of nutrient broth into a conical flask with a stopper and one a conical flask exposed to the air.

2. Using the hot plate, heat the two flasks to get rid of any living bacteria in the substance and let them sit at room temperature.

3. After several days, observe the difference between the two conical flasks. The flask with the stopper shouldnt have not changed significantly while the conical flask which is exposed the air should have changed in colour, thickness and smell.

Results:

Conical FlaskSmellColourThickness

Exposed To The AirSlight hint of smell arising from the substance The flask was discoloured while the colour of the nutrient broth was murky when compared to the other flask.The nutrient broth in the exposed flask seemed a little runny and was obvious that the substance had been heavily effected by the bacteria which had grown in the flask after the mixture had been heated.

Held By The StopperNo smell arose from the broth.The colour had stayed the same as after it was heated.The thickness of the substance had also not changed very significantly.

The results disapproved the long standing theory of spontaneous generation. If theory of spontaneous generations was real, the flask with the stopper would have become reinfected because the germs would have spontaneously generated but since this did not happen, this indicates that germs only come from other germs.

Discussion:

There are many differences between the experiment we conducted in class and the one Pasteur did. In our experiment, we used conical flasks while Pasteur used a curved-neck flask and this may impact our experiment because the curved-neck flasks have been built to retain the sterility of the substance while the conical flask was not built for this purpose, Pasteur also used a bunsen burner while our class used a hot plate and this is important in our experiment because a hot plate distributes the heat evenly while a bunsen burner distributes the heat inconsistently. The three variables which were controlled were the amount of protein broth, temperature of the hot plate and the air being able to access the protein broth (i.e the flask with the stopper and the flask exposed to the air). The independent variable was the bacteria growth in the open flask while the dependent variable was the time which both flasks where left for.My results support those of Pasteurs as it shows that spontaneous generation does not occur through the evidence that the flask with the stopper stays sterile while there is a build up of bacteria in the flask exposed to the air. When Pasteur was alive, many people believed in spontaneous generation which was the theory that all living things were created from non living things.The setup used in the experiment is reliable because it showed the build up of bacteria in one flask against a vastly different flask which looked clean and sterile.

Conclusion:

My hypothesis predicting that the flask with the stopper would stay the same therefore my prediction was correct. Pasteurs experiment showed that the theory of spontaneous generation was false and the experiment we have conducted in class also disapproved the theory.The flask with the stopper has stayed the same from the time it had been heated meaning it was still sterile while the flask exposed to the air, had been growing bacteria and also had significantly changed in colour,smell and thickness.