10T2K© The Scientific Method

Thing 1: The steps An observation leads to a question. A hypothesis is a testable answer to the question. An experiment is a test of the hypothesis. Data are findings from the experiment. Data may support or disprove a hypothesis.

Thing 2: A scientific hypothesis A scientific hypothesis must be testable. “Plants grow better if given extra nitrogen” is testable, so it’s a scientific hypothesis. “Plants grow better if they are happy” isn’t testable, so it’s not a scientific hypothesis. Non-scientific hypotheses may be correct; they’re just not testable.

Thing 3: Variables Anything that can be manipulated in an experiment is a variable. If you were testing what makes plants grow, variables would include Water Light Soil Fertilizer And more

Thing 4: Independent variables Independent variables aren’t affected by the experiment. In the experiment, “The effect of water on plant growth,” water is the independent variable. Water is unaffected by how much or little the plant grows.

Thing 5: Dependent variables Dependent variables can be affected by an experiment. In the experiment, “The effect of water on plant growth,” plant growth is the dependent variable. The amount of water affects plant growth. That is, plant growth is dependent on water.

Thing 6: Controls A control is used as a basis for comparison to the experimental treatment. If we want to see the effect of fertilizer on plant growth, we have to grow a control plant without any fertilizer for comparison.

Thing 7: A scientific theory. In science, a theory is a hypothesis that has so much evidence supporting it that it is generally considered true. Theories are not absolute truth. They can be modified or rejected based on new experimental data.

Thing 8: Redi and the maggots Francesco Redi showed that maggots come from flies, not spontaneous generation. An open jar of rotting meat has maggots growing in it after a few days. (That was Redi’s control!) A similar jar covered with gauze prevented flies from landing on the meat, so no maggots grew on the meat.

Thing 9: Louis Pasteur’s swan-neck flask Pasteur conducted a series of experiments to disprove spontaneous generation. Sterile broth in a swan-neck flask stayed clean even though it was exposed to the air. Allowing dust (containing microbes) from the air to contact the broth contaminated it.

Thing 10: Peer-reviewed research Peer-reviewed research is the most reliable source for scientific information. Before a research report is published, other scientists examine it to see if the research was performed properly.