1. Spontaneous Generation Before the 17 th century, people believed that living things could come from nonliving things. – The Cell Theory has not been written. Spontaneous generation – living organisms can originate from nonliving sources Example: Rotting meat Maggot

2. Redi’s Experiment Control group – Uncovered jar that contained meat Experimental group – Netting-covered jar containing meat – Allowed air to enter but prevented flies from landing on meat Results: Maggots seen in jar without netting, but not seen in jar with netting Conclusion: Visible living organisms cannot originate from nonliving sources

3. Spontaneous Generation and Microorganisms The invention of microscopes allowed people to discover microorganisms (bacteria). People believed these microorganisms developed spontaneously from the air. They believed the air had a life force that could create these bacteria.

4. John Needham’s experiment Created an experiment that was believed to prove spontaneous generation (every other scientist discussed today performed experiments that disproved spontaneous generation) Procedure: Briefly boiled a broth mixture in an open container and allowed it to cool to room temperature – He did this to kill all of the microorganisms in the broth (which is the same reason we cook things today) He would then later seal the containers Results: Microorganisms began to appear a few days later Conclusion: Needham concluded that these microorganisms had spontaneously generated from the life force in the air because he had killed all of the original bacteria in the broth

5. Needham’s Experiment

6. Problem with John Needham’s experiment He left the flasks open to the air to cool so other bacteria already present in the air could enter the container after the boiling of the broth. – These bacteria did not “spontaneously generate” from the “life force” in the air. The bacteria that were found in the broth were produced from the bacteria that entered the broth before concealment.

7. Spallanzani’s Experiment Spallanzani attempted to refine Needham’s experiment to disprove spontaneous generation. He performed basically the same experiment except with 2 differences: 1) He boiled the broth longer (to kill ALL of the microorganisms) and 2) He immediately capped off one of the containers. Results: Bacteria reappeared in the control group (uncapped flask) but no bacteria re-entered the experimental group (capped flask) Conclusion: Microorganisms come from other microorganisms (not from air).

8. Critics of Spallanzani Spallanzani’s results suggested that spontaneous generation was false because no bacteria grew in the closed flask while they did appear in the open flask. People who disagreed with Spallanzani argued that his experiment did not disprove spontaneous generation because he had killed the life force in the air by boiling it and then plugging the flask Since the life force in the flask was gone and no air could re-enter to replenish it then there was no life force to generate the bacteria.

9. Pasteur’s Experiment Louis Pasteur created an experiment where broth from boiled meat was placed in a curve- necked flask. – Air could enter through the neck, but solid particles (such as microorganisms) could not. (This was important because the “life force” would still be able to re-enter the flask after being boiled.)

10. Pasteur’s Experiment: Cont’d Results Broth in open flask began to show bacteria reappearance within a few days (control group). Broth boiled inside the curved-neck flask remained clear for one year. (experimental group). After necks were broken off, broth became cloudy and contaminated with microorganisms after one day. Conclusion Microorganisms come from other microorganisms (NO SPONTANEOUS GENERATION)

11. Spontaneous generation is false. Biogenesis is true. Each of these experiments played a role in debate of spontaneous generation vs. biogenesis. – Biogenesis – Living things come from other living things From these experiments, it was proven that spontaneous generation was false and that biogenesis was true.