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3.4 perform an investigation to model Pasteur’s experiment to identify the role of microbes in decay
perform an investigation to model Pasteur’s experiment to identify the role of microbes in decay
- Perform Pasteur’s experiment that showed that something from the air causes meat broth to go bad. As you conduct your experiment consider which variables need to be kept constant and be able to explain which are the dependent and which are independent variables.
Procedure:
- Use a meat extract cube to make a clear broth.
- Use two conical flasks instead of Pasteur’s balloon flasks. Fit the flasks with one-holed stoppers. Use glass tubing bent into an S-shape to replace Pasteur’s swan-necked flask. Place a straight piece of glass tubing in the other flask.
- Put some broth into both flasks and boil gently for fifteen minutes.
- Leave both flasks, not in direct sunlight for several weeks. Every two or three days compare the contents of the two flasks. Look for cloudiness, scum, bubbles and mould colonies. Record your results.
- Assess the accuracy of your observation and the relative importance of the data gathered. You could do this by comparing your experiment with the description of Pasteur’s experiment, which follows.
Pasteur’s experiment
- When Pasteur did his experiment, the broth in the swan-necked flask remained clear for several weeks, while that in the open flask quickly became cloudy and smelly.
- Both flasks were open to the air. In the swan-necked flask, air could move freely through the neck of the flask just as it did in the straight-necked flask, but the much heavier micro-organisms, in the air, were trapped in the bottom part of the S-curve.
- This experiment showed that for the broth to grow micro-organisms and start to decay, there had to be access to air containing the spores of micro-organisms.
Pasteur’s experiment 