Introduction to The Scientific Method

A. Russo-NeustadtCSULA

What is the Scientific Method?

A system of investigation that consists of three major steps:Step 1 = gathering facts or making an observationStep 2 = developing a hypothesis (explanation) to explain your observationStep 3 = testing your hypothesis

Step 1 for Primrose Example

Observation = Plants on the northern side of your house are large and blooming profusely, while those on the southern side of the house are small, with few blooms

Step 2 for Primrose Example

Note the following – Soil is dry on the southern side of the

house, but moist on the northern side of the house, thus,

Hypothesis = The primroses on the southern side of the house show poor growth because the soil there is too dry.

Step 3 Testing Your Hypothesis Requires Four Sub-steps

Designing an experiment Making a prediction about the

outcome of the experiment (based on the assumption that your hypothesis is correct)

Conducting the experiment and collecting data (results)

Drawing a conclusion = interpreting the results of the experiment

What is an Experiment?

A scientific investigation carried out under controlled conditions.

Controlled conditions refers to the attempt to regulate all variables that could influence the outcome of the experiment except the variable under investigation

Examples of important variables for the primrose example?

Experimental Design for the Primrose Example

Give the plants on the southern side of the house enough water to keep the soil as moist as it is on the northern side of the house

Prediction for the Primrose Example

Predictions are “If, then” statements and look like - If “my hypothesis is correct”, then “the

following should happen during my experiment”.

If the plants on the southern side of the house show poor growth because the soil there is too dry, then…?

Conducting the Experiment for the Primrose Example

Add additional water to the plants on the southern side of the house so that the soil moisture is approximately equal to that on the northern side of the house.

Conduct experiment for (how long?) Result (data) = ?

Conclusion for the Primrose Example

Differences in soil moisture are NOT responsible for the differences in plant growth observed between those primroses planted on the northern versus southern sides of the house.

What Do We Do Now?

Modify our original hypothesis based on the outcome of our first experiment (return to step 2 and repeat process)

Modified Hypothesis = The primroses on the southern side of the house show poor growth because they receive too much sunlight.

Step 3 for Modified Hypothesis

Experimental Design – Use shade cloth to reduce the amount of sunlight received by the primroses on the southern side of the house to an amount equal to that received by plants on the northern side of the house.

Step 3 for Modified Hypothesis (continued)

Prediction = If the primroses on the southern side of the house show poor growth because they receive too much sunlight, then...?

Step 3 for Modified Hypothesis (continued)

Conducting the Experiment – Shade plants of the southern side of

the house such that they receive +/- the same amount of sunlight as those on the northern side of the house

Conduct experiment for (how long?) Results (data) = ?

Step 3 for Modified Hypothesis (continued)

Conclusion = Differences in sunlight experienced by plants on the northern versus southern side of the house may have been an important factor in their growth differences.

A Note of Caution The scientific method never allows us

to conclusively prove an hypothesis. Instead, the scientific method is

designed to disprove an hypothesis. (For example, our original hypothesis in today’s example.) The original hypothesis is then modified and tested until a hypothesis is developed that cannot be proven incorrect.

What is a Scientific Theory? A hypothesis that has been tested in many

different ways (i.e. with different experimental designs), many times and by many different scientists, but can not be proven incorrect

So much evidence has been assembled in favor of an hypothesis that the scientific community is reasonably certain (but never absolutely sure) that the hypothesis is correct

The scientific community is still open to modification of the theory, if appropriate evidence is produced

Another Example

Francisco Redi was an Italian physician-scientist who demonstrated that spontaneous generation (production of life from non-living things) was not required to explain the appearance of maggots in spoiled meat.

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Redi noticed that flies swarm around meat left exposed to the air and that maggots appear in the meat a few days later.

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He thought that perhaps the maggots did not arise spontaneously from the non-living meat, as was commonly believed at the time, but that instead the maggots were produced by the flies.

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In order to test this explanation, hecleaned two similar jars and put the

sameamount of fresh meat, without maggots,in each jar. He then covered one jar withgauze, so that no flies could enter, andleft the other jar open to the flies.

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He placed the jars on the same window

ledge and was careful to keep thetemperature, light exposure and

humiditythe same in both jars.

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He thought to himself, “If the fliesproduce the maggots, then

preventingtheir access to the meat should

preventproduction of maggots”.

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After several days, Redi noticed thatmaggots appeared in the meat in

theopen jar, but not in the jar covered

withgauze.

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He decided that the results of thisexperiment suggested that the

maggotsare produced by the flies and not byspontaneous generation of life within

themeat.

When Redi cleaned two similar jars, put the same amount of fresh meat in each jar and covered one jar with gauze and left the other jar open to the flies he was:

A. Making an observationB. Designing an experimentC. Making a predictionD. Developing a hypothesis

When Redi cleaned two similar jars, put the same amount of fresh meat in each jar and covered one jar with gauze and left the other jar open to the flies he was:

A. Making an observationB. Designing an experimentC. Making a predictionD. Developing a hypothesis

When Redi noticed that flies swarm around meat left exposed to the air and that maggots appear in the meat a few days later he was:

A. Making a PredictionB. Developing a hypothesisC. Drawing a conclusionD. Making an observation

When Redi noticed that flies swarm around meat left exposed to the air and that maggots appear in the meat a few days later he was:

A. Making a PredictionB. Developing a hypothesisC. Drawing a conclusionD. Making an observation

When Redi decided that the results of his experiment suggested that the maggots are produced by the flies and not by spontaneous generation of life within the meat he was:

A. Drawing a conclusionB. Making an observationC. Controlling the variablesD. Making a prediction

When Redi decided that the results of his experiment suggested that the maggots are produced by the flies and not by spontaneous generation of life within the meat he was:

A. Drawing a conclusionB. Making an observationC. Controlling the variablesD. Making a prediction

When Redi thought “perhaps maggots do not arise spontaneously from non-living meat, but instead are produced by the flies” he was:

A. Making an observationB. Developing a hypothesisC. Drawing a conclusionD. Gathering facts

When Redi thought “perhaps maggots do not arise spontaneously from non-living meat, but instead are produced by the flies” he was:

A. Making an observationB. Developing a hypothesisC. Drawing a conclusionD. Gathering facts

When Redi developed his If-Then statement he was:

A. Making a hypothesisB. Making an observationC. Making a predictionD. Making cookies

When Redi developed his If-Then statement he was:

A. Making a hypothesisB. Making an observationC. Making a predictionD. Making cookies

In the experiment described above, Redi was careful to make sure that both the experimental and the control jars were maintained at the same temperature and humidity, and received the same amount of light. He took these precautions because he wanted to conduct his experiment under controlled conditions. In Redi’s experiment temperature, humidity and amount of light represent the:a.Observations, b. Replicates, c. Variables,

d. Results, e. Conclusions.

In the experiment described above, Redi was careful to make sure that both the experimental and the control jars were maintained at the same temperature and humidity, and received the same amount of light. He took these precautions because he wanted to conduct his experiment under controlled conditions. In Redi’s experiment temperature, humidity and amount of light represent the:a.Observations, b. Replicates, c. Variables,

d. Results, e. Conclusions.