Observation vs. Inference Variables Spontaneous Generation Experimental Design Observation vs. Inference Variables Spontaneous Generation

Observation vs. Inference Observation – something we can see or can experience through our senses (taste, feel, see, hear, etc) Quantitative Qualitative Inference – something we think will happen based on our observations, something we know from prior knowledge

Quantitative vs. Qualitative Recorded as measurements Qualitative Recorded as descriptions

Variables Control – used for comparison Dependent Variable – variables that change based on the independent variable Independent Variable – variables that the experimenter changes

Scientific Method Purpose Research/Hypothesis Experiment Analysis Making predictions using observations/inferences Research/Hypothesis Find out as much as you can then form a hypothesis “If…Then…” Experiment Carry out an experiment using control and variables Analysis Make observations and collect data Conclusions Review the data and then accept/reject the hypothesis Repeat Make sure the results are repeatable

Designing an Experiment How could you decrease a person’s blood pressure? Hypothesis: Control: Dependent variable: Independent variable:

Abiogenesis Before the 1600s, it was generally thought that organisms could arise from nonliving material by spontaneous generation

copyright cmassengale Aristotle (384 –322 BC) Proposed the theory of spontaneous generation Also called abiogenesis Idea that living things can arise from nonliving matter Idea lasted almost 2000 years copyright cmassengale

Examples of Spontaneous Generation copyright cmassengale

copyright cmassengale Example #1 Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times copyright cmassengale

copyright cmassengale Example #1 Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs copyright cmassengale

copyright cmassengale Example #2 Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around. copyright cmassengale

copyright cmassengale Example 2 Conclusion: It was obvious to them that the mice came from the moldy grain. copyright cmassengale

Disproving Spontaneous Generation copyright cmassengale

copyright cmassengale Francesco Redi (1668) In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat copyright cmassengale

copyright cmassengale Redi’s Experiment Redi used open & closed flasks which contained meat. His hypothesis was that rotten meat does not turn into flies. He observed these flasks to see in which one(s) maggots would develop. copyright cmassengale

copyright cmassengale Redi’s Findings He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within. In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared. copyright cmassengale

Redi Redi showed in 1668 that rotting meat kept away from flies would not produce new flies Maggots appeared only on meat that had been exposed to flies

Did Redi Use the Scientific Method? copyright cmassengale

copyright cmassengale The Scientific Method Observation Hypothesis Experiment Accept, Reject, or Modify hypothesis copyright cmassengale

Lazzaro Spallanzani’s (1765) Boiled soups for almost an hour and sealed containers by melting the slender necks closed. The soups remained clear. Later, he broke the seals & the soups became cloudy with microbes. copyright cmassengale

Spallanzani’s Results copyright cmassengale

copyright cmassengale Conclusion Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” Therefore, spontaneous generation remained the theory of the time copyright cmassengale

Spallanzani Spallanzani showed in the 1700s that microorganisms would not grow in broth when its container was heated and then sealed This seemed to indicate that microorganisms that cause food spoilage do not arise from spontaneous generation but, rather, are carried in the air

The Theory Finally Changes copyright cmassengale

Pasteur Pasteur used a variation of Spallanzani’s design to prove that microorganisms are carried in the air and do not arise by spontaneous generation

copyright cmassengale Pasteur's Problem Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself. Pasteur put broth into several special S-shaped flasks Each flask was boiled and placed at various locations copyright cmassengale

Pasteur's Experiment - Step 1 S-shaped Flask Filled with broth The special shaped was intended to trap any dust particles containing bacteria copyright cmassengale

Pasteur's Experiment - Step 2 Flasks boiled Microbes Killed copyright cmassengale

Pasteur's Experiment - Step 3 Flask left at various locations Did not turn cloudy Microbes not found Notice the dust that collected in the neck of the flask copyright cmassengale

Pasteur's Experimental Results copyright cmassengale

The Theory of Biogenesis Pasteur’s S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis copyright cmassengale Figure 1.3