An Introduction to Biology: The Scientific Method and Pasteur's Experiment

The Scientific Method

• Flow of the scientific method:

  • Observation

  • Question

  • Hypothesis

  • Prediction

  • Experiment or Observation

  • Conclusion

• Next steps based on experimental outcomes:

  • Hypothesis supported: Make more predictions.

  • Hypothesis not supported: Pose new hypothesis.

Caveats Regarding Hypothesis Testing

• Every assertion regarding the natural world is subject to challenge & revision (if based on evidence).

• Results obtained in experiments must be reproducible.

• Any scientific hypothesis or claim must be both testable & falsifiable.

Pasteur's Flask Experiment and Conclusion

• Experimental process:

  • Nonsterile liquid is poured into a flask.

  • The neck of the flask is drawn out in a flame.

  • Liquid is sterilized by heating, forcing air out the open end.

  • Liquid cooled slowly; dust and microorganisms are trapped in the bend.

• Observations over time:

  • Long time: Liquid remains sterile for many years.

  • Short time: Flask tipped so microorganism-laden dust contacts sterile liquid, leading to microorganisms growing in liquid.

• Conclusion: Life arises as a result of contamination by airborne microscopic organisms (Hypothesis 2).