1.2 – Publishing and Repeating Investigations

Redi’s Experiment on Spontaneous Generation Section 1-2 OBSERVATIONS: Flies land on meat that is left uncovered. Later, maggots appear on the meat. HYPOTHESIS: If the jars are left uncovered, maggots will appear. PROCEDURE Uncovered jars Covered jars Controlled Variables: jars, type of meat, location, temperature, time Several days pass Manipulated Variables: gauze covering that keeps flies away from meat Responding Variable: whether maggots appear Maggots appear No maggots appear CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur. Go to Section: 12/4/2018

Publishing and Repeating Investigations Results of experiments should always be the same if the same variables are manipulated This is why experiments are published and why they can be performed and tested by others 12/4/2018

Anton van Leeuwenhoek Later tests of Redi’s experiment were influenced by Leeuwenhoek’s making of lenses that could magnify things He discovered tiny moving objects in rainwater, pond water and dust He called the “animalcules” The discovery had major implications on spontaneous generation 12/4/2018

Needham In the mid-1700’s John Needham worked with animalcules to attack Redi’s work He heated a flask of gravy, sealed it and waited several days After the wait he found that the gravy was swarming with activities Spontaneous generation 12/4/2018

Figure 1-10 Spallanzani’s Experiment Section 1-2 Spallanzani did not believe that Needham heated the broth enough to kill all the organisms in it. Gravy is boiled. Flask is open. Gravy is teeming with microorganisms. Flask is sealed. Gravy is free of microorganisms. Gravy is boiled. Go to Section: 12/4/2018

Section 1-2 How Scientists Work Publishing and Repeating Investigations 16. He designed a special S shaped tube that allowed air into the flask but protected microorganisms from entering the flask. Microorganisms got stuck in the tube. 12/4/2018

Louis Pasteur In the 1800’s arguments were still being tested for spontaneous generation They believed air was the “life force” needed Pasteur came up with an experiment with a curved neck added to test the air idea Because of this he solved many problems – souring of wine and the biggest was the idea of infectious disease 12/4/2018

Figure 1-11 Pasteur’s Experiment Section 1-2 Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms. (just like Spallanzani) Go to Section: 12/4/2018

Figure 1-11 Pasteur’s Experiment Section 1-2 Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms. Go to Section: 12/4/2018

Figure 1-11 Pasteur’s Experiment Section 1-2 Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms. Go to Section: 12/4/2018

Figure 1-11 Pasteur’s Experiment Section 1-2 Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms. Go to Section: 12/4/2018

When Experiments Are not Possible When subjects need to not be disturbed Ethical issues 12/4/2018

When experiments are not possible? 18. They identify as many as possible so that most variables are controlled. Example: It is difficult to run a controlled experiment during human medical studies….WHY? Different ages Different races Different genetic makeup Different pre existing medical conditions Goal would be to try to find subjects that are as similar as possible (but it never will be truly controlled) 12/4/2018

How a Theory Develops Theory occurs when a hypothesis becomes very well supported In science, the word theory applies to a well tested explanation that unifies a broad range of observations 12/4/2018

How a Theory Develops Oh, that is just one person’s theory! (Poor use of the word theory) A theory is a well tested explanation that explains many observations Theory of evolution explains the following observations… Why our DNA is so similar to other humans (99.9%) Why our DNA is so similar to other species (>98%) Why fossils deep in layers are extinct and less complex Why medicine that use to work on bacteria doesn’t anymore (resistance) Why things are so adapted to their environment 12/4/2018