RHP 5: Controlled Experiment 21 February 2019 LHP 4: Variables RHP 5: Controlled Experiment Compare and Contrast: Manipulated / Responding / Controlled Variables

Experiments Used to test a hypothesis Generate data

Designing an Experiment State the problem/ask a question. Form a hypothesis [null hypothesis]. Set up a controlled experiment. Record and analyze results. Draw a conclusion But….. It doesn’t stop there! Retest and share the results.

In a controlled experiment a scientist isolates and tests a single variable. Manipulated variable (Independent variable) This is changed by the experimenter. Only one variable should be manipulated by the scientist. Responding variable (Dependent variable) This is the variable measured by the experimenter Controlled variables All other variables are kept the same

IAN LHP Create a Venn Diagram Compare and contrast manipulated, responding, and controlled variables. Give at least 3 bullet points for each

RHP 7: Famous Experiments 21 February 2019 LHP 6: Variables RHP 7: Famous Experiments Create a chart that identifies the independent, dependent, and controlled variables for Redi’s, Spallanzani’s, and Pasteur’s experiments.

Famous Experiments

Francisco Redi 1600s popular belief was that flies and other creatures would spontaneously generate from nonliving matter. 1668 Redi proposed a different hypothesis. Observed flies landing on chunks of meat, then several days later maggots appear. Hypothesized that maggots came from the flies, not the dead meat. In other words, life only comes from living organisms.

1668

Needham’s Experiment Heated gravy to kill microorganisms, then sealed the flask After several days gravy was teeming with microbes Claimed organisms spontaneously generated

Spallanzani’s Experiment Didn’t think Needham heated flask enough to kill microorganisms Repeated experiment, but boiled broth thoroughly Sealed flask did not grow microbes, open flask did Findings not accepted by many scientists because sealed flask did not allow “life force” in

Pasteur’s Experiment (1864) Repeated experiment using a flask with a special neck that allowed air into it Remained free of microorganisms until the neck was removed

Why do scientists publish their procedures and results of their experiments? So their work can be repeated. Their procedures can be reviewed. And, others can try to reproduce their results.

Hypothesis vs. Theory A hypothesis is a possible explanation for a problem. A theory has been well tested and unifies many observations. What started as Redi’s hypothesis in the 1600’s eventually became the theory of biogenesis [life must come from other living things].

IAN LHP Create a chart that identifies the independent, dependent, and controlled variables for Redi’s, Spallanzani’s, and Pasteur’s experiments.