Scientific Method

Lab 1: Scientific Method

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Introduction:

What is the Scientific Method?

Science
is based upon a logical progression of questions and answers known as the
scientific method. This method of reasoning is based on orderly, unbiased
information gathered through a series of steps.

The
first step is making an observation
and questioning an event or problem.
For example, Jane went to the store and purchased a plant when she moved into
town. After three weeks, Jane’s plant died. The death of Jane’s plant is our
observation.

The
next step in the scientific method is to formulate
a hypothesis. A hypothesis is a possible explanation or answer to the event
or problem that is both tentative and testable. Also, a hypothesis is either
supported by the evidence or rejected; it is never proven. For Jane’s plant death, a possible hypothesis
would be that the plant received too much water, which caused it to die.

The
next step would be to test the
hypothesis through a controlled
experiment. Which for Jane’s plant, she could set up an experiment that
measures the amount of water that a plant receives.

The
next step occurs when Jane would make an analysis
of results from her experiment.

And
the final step of the scientific method is the conclusion. In the conclusion, the data gathered from the
experiment is either used to support the hypothesis or refute the hypothesis.
If the data do not support the hypothesis, then you can create a new hypothesis
and try again!

Designing a Good Experiment
The most challenging part of the scientific method is usually the
third step, designing and carrying out an experiment to test the hypothesis. A
well-designed experiment should include all of the following characteristics:

1. An independent variable. The
independent variable is the part of the experiment that the scientist changes
or manipulates to see what effect occurs.
“The temperature is the
independent variable, since that is what the experiment changes to see its
effect.”

2. A dependent variable. The
dependent variable is the part of the experiment that changes because of the change
in the independent variable. In other words, the dependent variable is the
effect that occurs from changing the independent variable.
“The metabolic rate of the mice is the
dependent variable, since the enzymatic activity necessary for cellular metabolism
is impacted by temperature.

3. An experimental group. The
experimental group is the group of subjects where the independent variable is
set to an unusual or test level.
“The mice are placed at 10 degrees Celsius are
the experimental group, since the effect of lower temperature on the metabolic
rate of mice is what is being tested.”

4. A control group. A control
group is the group of subjects in the experiment that the experimental group is
compared to. For the control group, the independent variable is set to a normal
or usual level (which may be zero, if that is considered a normal level).
“The mice are kept at 25 degrees Celsius are
the control group, since this is the optimal temperature for the metabolic rate
of mice.”
Some experiments include things called positive controls and
negative controls. These are slightly different than control groups. Positive
and negative controls serve to show that the experiment is working correctly.
A positive control is a part of the experiment
that is deliberately designed to give a positive result. It shows that the
experiment is capable of producing a positive result when it is supposed to.
A negative control is a part of the experiment
that is designed to give a negative result. It shows that the experiment is capable
of producing a negative result when it is supposed to.

5. The experiment should contain repetition (aka
replicants). This means that there should be more than one subject in the
experimental group and the control group. Why? In general, the more repetition,
the less likely that your results are due to random chance.
“The experimental group and the control group
each contained 100 mice.”

6. The experiment should be well defined. One
aspect of “well defined” is that the procedure (the steps) must be written down
and clearly described. The true test of a well written experimental procedure
is that another scientist could duplicate it exactly using just the written
directions. Another aspect of “well defined” is that everything in the
experiment, such as the materials, chemicals, equipment, environmental
conditions, and the subjects (the organisms involved in the experiment), should
be described as exactly as possible. All of the factors that are kept equal in
the experiment and control groups are called standardized
variables. Another aspect of “well defined” is that all parts of the
experiment should be quantified. This means they should be measured by numbers.
a) All mice in this experiment are
the same species (Drosophila melanogaster) and same age class. All mice were
placed in growth chambers and fed standard mouse feed. The
experimental group of 100 mice were placed in the incubator set to 10 degrees
Celsius. The control group 100 mice were placed in an incubator set to 25
degrees Celsius. In order to accurately
determine the metabolic rate of the mice, each incubator contained carbon
dioxide and oxygen sensors that continuously collected gas exchange data. Each iteration of this experiment was
conducted for three hours.
This activity was modified from the Scientific
Method Tutorial by Dr. Katherine Harris is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 3.0 Unported License.

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