The Scientific Theory

topic 1

Ignaz Semmelweis

• Studied why puerperal fever was 5X more common in births attended by doctors than midwives

• Fewer women died on the streets than in the clinic, and he found this unacceptable so he did lots of testing

Ignaz Semmelweis's solution

• Proposed the disease can be transferred by physical contact

• Male doctors did dissections and never washed their hands

• Solution = Chlorine handwash which led to decreased mortality rates

The problem with Semmelweis's experiment

• The results didn’t fit with the hypothesis

• No causative mechanism was explained

• No proper control group

• Confirmation bias (doctors were certain their incorrect practices were correct so they went back to no handwashing)

Louis Pasteur (1859)

• Supported the idea that cells come from pre-existing cells (Germ Theory)

• Bacteria doesn’t spontaneously arise

• led to the understanding that cells have genetic info and its passed during cell divison

What famous experiment is linked to Louis Pasteur?

The Swan Neck (S. Neck) Experiment

What is Characterization in the scientific method?

Look at the system, try to understand it based on the current info we have, ask a question that will add new info to the current one.

Hypothesis

An educated guess; considers confirmation bias; what we think will happen/the right answer.

Experiment (scientific method)

Allows us to test/reject the hypothesis.

Nuisance Variables/Confounding Factors?

Factors that weren't taken into account that could impact the experiment.

Control variable/group

Ensures the correlation between independent/dependent variables match up.

What are the main components of a scientific experiment?

What make the elements work

• hypothesis

• independent variable

• dependent variable

• nuisance/confounding variables

• control (variable/group)

What is the Independent Variable?

What you change/manipulate in the experiment

Dependent Variable

The result that comes from the independent variable (what you measure/observe).

How do nuisance/confounding variables fit into the components?

Factors that could mess up results if not accounted for

How do controls fit into the components?

The group/variable setup to make sure any changes really come from the independent variable (helps isolate the effect).

The S. Neck experiment

• beef broth is placed in the flask and boiled to sterilize

• the curved neck allowed air but trapped microbes

• tilting the flask let microbes reach the broth (proof was the broth got cloudy)

• conclusion: demonstrates that cells come from pre-existing cells