The Scientific Method

Recipe for Bees About 2000 years ago, a roman poet wrote these directions for producing bees: 1.Kill a bull during the first thaw of winter. 2.Build a shed. 3.Place the dead bull on branches and herbs inside the shed. 4.Wait for summer. The decaying body of the bull will produce bees.

Why do you think reasonable individuals once accepted this idea about bees as scientific fact? ???

Observation v. Inference An observation is something determined directly from one of your senses (sight, taste, touch, hearing, smell) An inference is something determined from an observation and some prior knowledge

Observation vs. Inference StatementObservationInference Object A is round and orange Object A is a basketball Object C is round and black and white Object C is larger than Object B Object B is smooth and white Object B is a ping-pong ball Each object is used in a different sport

Using Observations & Inference 2,300 years ago, Aristotle (in Pink) used his five senses and made observations about nature based on reason and rules of organization (Ex. Recipe for Bees)

So, based on observation and Reason, People thought for many years, that the sudden appearance of organisms occurred because they simply “arose” out of non-living matter This idea was called spontaneous Generation

Spontaneous Generation Examples Mice in Grain covered by an old shirt Maggots on meat

Only about 400 years ago, people began to doubt these ideas Why then?

Francesco Redi In 1668, Francesco Redi challenged the accepted idea that maggots arise from meat

Observations First Every experiment starts with observations. Redi had observed that flies land on uncovered meat and afterwards maggots appeared.

Using Inference, Redi made a Hypothesis Redi proposed that flies must produce maggots A hypothesis is a possible explanation for something based on observations and inference

Redi then Came up with a Controlled Experiment… Where only one variable is changed at a time. All others are kept unchanged to see if the first one is the cause of the effect you are testing.

Redi’s Experiment Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear

Independent Variable – conditions or things that don’t change in an experiment Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear Independent Variables: jars, type of meat, location, temperature, time

Dependent Variable – conditions or things that do change in an experiment Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear Dependent Variable: gauze covering that keeps flies away from meat (usually only 1 at at time - why?)

Control Group – the normal group used as the basis for comparison Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear Control Group – uncovered jars

Experimental Group – group that is being tested Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear Experimental Group – covered jars

Redi was not the first scientist… …to make experiments, but he is remembered because he kept written records of his work and results so that others would know what happened even after he died (also called data).

Conclusion – explanation of the results of the experiment Uncovered jarsCovered jars Several days pass Maggots appear No maggots appear CONCLUSION - Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

A Theory.. …is a well-tested explanation that ties a lot of observations together - Comes from repeated experiments by different people

Theories enable scientists to make accurate predictions about new situations For example, after redi’s experiment, what can we predict about mice coming from grain? Does knowing this theory mean we don’t need to test our new hypothesis?

With a New Hypothesis… …the whole process begins again. Observation Hypothesis Controlled Experiment Data Conclusions (And possibly a theory) Conclusions (And possibly a theory)