The Scientific Method The scientific method Is how

The Scientific Method

The scientific method • Is how scientists as questions about the world and test the answers • In other fields: art, philosophy, music, history, specialists ask questions about the world • The scientific method is different

The scientific method defined: • The scientific method – Is a system of asking questions and then – Developing explanations and then – Testing these explanations against the reality of the natural world

Steps in the scientific method (1) • State a specific problem or question based on an observation of the natural world – A fact is a repeatable observation • With the problem in mind propose an explanation for what you observe. This explanation is the hypothesis

Steps in the scientific method (2) • Test the hypothesis – One way is to make more observations and see if they are ALL consistent with your hypothesis – Another way is set up a controlled test of the hypothesis. This is called the experiment • Controlled test means you have a control group of test subjects and an experimental group of test subjects

Steps in the scientific method (3) • Analyze the results of the experiment – Sometimes the results are clear cut and obvious; your hypothesis stands up (=correct) or it does not (=incorrect) – Sometimes the results suggest a new hypothesis; you start the process over again until your hypothesis is correct

The experiment • Control group: the benchmark – You treat the subjects or articles in the control group exactly the same as those in the experimental group but without the treatment you are testing • Experimental group – You vary one condition (the variable) and keep all other conditions the same as in the control group

The experiment • You collect data in an experiment • You summarize the data mathematically – Mean, mode, medium, range • You compare the data summary of the experimental group with the control group – Statistical tools are used – Compare means, standard deviations, variances

Three experiments to consider • Tomato experiment – Text page 14, see figure 1. 10 • Yellow fever experiment – Text page 17 -19 • Pasteur’s experiment

Louis Pasteur’s experiment • • • Hypothesis: “omnis cellula e cellua” Famous goose neck flask experiment Control flasks Experimental flasks Results confirm hypothesis (now theory) of biogenesis • Disproved hypothesis of spontaneous generation

Spontaneous Generation (1) • Up until the 17 th century biologists thought that simple living things appeared spontaneously • Francisco Redi did the famous decaying meat experiment – Control: decaying meat covered with a cloth – Experimental: decaying meat open to the air – No maggots in the control

Spontaneous Generation (2) • Spontaneous generation idea was revived with the invention of the microscope • Microorganisms and small animals seemed to appear spontaneously in water or broth • Pasteur’s experiment disproved spontaneous generation for the second time