Modeling Pasteur's Experiment

Modeling Pasteur’s Experiment

Name: Ella Shen

Teacher’s name: Mr. Dayaram

Course: Biology HL

Date: 20.9.2017

Introduction:

In the 19 century, spontaneous generation was proposed which believes that all organisms are come from inanimate matter. (Ball, 2016) And in the years following, a scientist called Louis Pasteur did an experiment to disprove the hypothesis. In the experiment, he boiled broth in a flask with a swan neck and broth in a normal flask without swan neck. The broth in flask without swan neck decayed in short time but the broth in flask with swan neck remained unchanged. (Levine and Evers, 1999) And according to the cell theory, cell only arise from pre-existing cells.

The purpose of the experiment is proving the bacteria is not produced naturally but produced by the pre-existing bacteria.

The control group of the experiment is the flask two with a rubber stopper. The experimental group is the flask one without a rubber stopper. The independent variable is if cover the flask with rubber stopper, the dependent variable is the change of the chicken stock, like bacteria produced.

There is a hypothesis that the chicken stock in the conical flask without a rubber stopper will change and bacteria will be produced.

Procedure:

        Materials:

- graduated cylinder (100ml)

- 2 conical flasks (100ml)

- burner

- match

- wire gauze mat

- stand

- timer

- chicken stock

- stirring rod

- crucible tongs

- rubber stopper

- inoculating loop

- petri dish

1. the 100ml of the chicken stock was measured by graduated cylinder it was added into a conical flask and the conical flask labelled as flask one.
2. Another 100ml of chicken stock was measure by graduated cylinder was added into a conical flask and the flask was labelled as flask two.
3. The burner was lighted by match and putted under the stand. The wire gauze mat was putted on the stand.
4. The flask one was putted on the stand and boiled for 15 minutes.
5. The flask one was took down by crucible tongs.
6. The flask two was putted on the stand and boiled for 15 minutes, too.
7. The flask two was took down by crucible tongs and covered with a sterilized rubber stopper.
8. The two boiled flasks were putted away and stayed there for few days.  
9. The inoculating loop burned with the burner.
10. The inoculating loop cooled down and was putted into flask 1.
11. The bland side named “S” side of petri dish was wiped with liquid from flask 1 with inoculating loop.
12. The petri dish stayed for few days.

Results:

Discussion and Evaluation:

The hypothesis was supported because the flask one without rubber stopper became cloudy and dark after few days, however, the chicken stock in the flask two with a rubber stopper did not change. And the microorganism grew on the “S” side of the petri dish looked similar with bacteria grew on the “B” side because of the color, shape and size. And so, we know that bacteria produced by pre-existing bacteria but not produced naturally.