The Scientific Method

1.6 The Scientific Method



After completion of this activity students will be able to:

  1. apply the scientific method in experiment design and analysis;
  2. use appropriate academic resources to research and evaluate environmental issues;
  3. demonstrate how natural systems operate and interrelate with one another; and
  4. evaluate and graph experimental data for aquatic ecosystems.

Introduction: The Scientific Method

The scientific method is just a way to use critical thinking.  Many people do not check out the facts of the latest email story and just pass it along to friends.  For example, dihydrogen monoxide (DHMO) is seen by some as the latest chemical threat on college campuses.  But what is it really? (see Hint- do some lateral research to find out what DHMO really is….

Title: Caution DHMO Symbol

For more fun items like this, read this satirical article from The Onion ( that some people might not realize these stories and articles are not true.  For example, review the article EPA: Stubborn Environment Refusing to Meet Civilization Halfway (,17418/) and see if you can find any information that might mislead you to the meaning of the article.  If you can figure out what DHMO really is, then you don’t have anything to worry about in science class.  If you did not, then this is an opportunity to train yourself to think a little more critically and become more comfortable with science.

Much of science involves observation and recording those observations and making sense out of them.  Sometimes science involves deliberate experimentation in which variables are manipulated and the results help determine the relationship of those variables.  Whether you are making observations of the world, or doing experiments, each involves collecting data, analyzing the data, and developing conclusions that someone else can replicate.  If you design and build a kitchen table, you would want to write the instructions in a way in which your neighbor or friend could use your design and build the same table.  That is the way with the scientific method – you want to make sure the observations you make, experiment you conduct, and the analysis you do can be done by anyone else and that they would get the same results.

Your hypothesis is an idea about the relationship of variables, or even whether a news article is really factual, and you test it with observations (research) or experimentation and then determine whether the hypothesis is supported or not.  While a hypothesis is an idea, a theory is a well-founded explanation based on testing using the scientific method.  Most well-known scientific theories have been tested many times and not shown to be false.  The term “theory” is also used in common language to suggest an idea, but a scientific theory is based on testing, such as the Cell Theory.

Title: Example Bar Graph - Description: Acreage of Bay Grass by year

In this class, your hypothesis should specifically predict the behavior of the dependent variable (what will be changing depending on the other variable, the independent variable).  Take a look at the graph above of Bay Grass Abundance (acreage) vs time (i.e., year) – ( The dependent variable is always on the Y-axis (side) of a graph (e.g., Bay Grass Abundance) and the independent variable on the bottom, or X-axis (e.g., year).  The Bay Grass acreage is changing depending on the year.

You may find it easier to write your hypothesis in the form of IF, THEN, such as IF I add drops of vinegar to water (the number of drops added would be on the x-axis), THEN the pH in the water will decrease (pH would be on the y-axis). Using To learn more about independent and dependent variables, check out

Once you have made your hypothesis, the next step is to test it by performing an experiment.  Experiments must control for all variable except the one you are looking at.  So the conditions must be identical except for the dependent variable, in this case the acreage.  Each experiment must also have a control group.  This means a group that the variable is unchanged.  For example, if you are doing an experiment looking at how shortened sunlight affects leaf fall in oak trees, the experimental group of trees would have shortened amounts of daylight, but the control group would have trees with a constant amount of daylight.  By comparing the control group and the experimental group, we can determine if the change was really caused by the amount of sunlight or if another variable is at play.

The fun just starting after the experiment is done.  Now you have to analyze your data.  Data analysis involves grouping the data into tables and graphs that show the relationship between the two variables.  Looking at the tables and graphs should give you an answer as to whether to accept or reject your hypothesis, which is the final step of the Scientific Method.  If the data matches your hypothesis, then you can accept it, but if the data does not, you reject it and come up with another hypothesis and start over again!

Analysis Questions:

Please respond to the following:

  1. Conduct online research describing the relationship of dissolved oxygen concentration and fish populations (number of fish) using at least 3 reputable and/or scholarly sources.  Write 1-2 paragraphs (at least 300 words) describing what you have learned during your research.  Use APA style formatting for both the in-text citations and the end of text citations.
  • Based on your research, formulate a hypothesis on the expected relationship between the number of fish found and the dissolved oxygen concentrations.  Remember to use an IF-THEN format and only include the two variables of fish and dissolved oxygen.
  • Create a scatter plot graph of the data set and include a trendline.  Identify the dependent (y-axis) and independent variables (x-axis).  You should not include the pond number, but please do provide a title for the graph, and include a title for each axis, and the units for each axis.
Pond NumberDissolved Oxygen (mg/L)Fish (#/seine)
  • Based on the data in the table above, determine whether you would accept, or reject, your hypothesis.  Please make sure to explain your reasoning.
  • Does the number of fish affect the dissolved oxygen, or does the dissolved oxygen affect the number of fish?  Please explain your reasoning.
  • Please identify the relationship between DHMO, oxygen and fish populations and explain your reasoning.  Also, explain whether you think DHMO is toxic to fish (why or why not).  Please also include the most common name for DHMO. Cite your sources!
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