3 1.4 Scientific Investigations

Created by: CK-12/Adapted by: Christine Miller

“Doing” Science

Science is as much about doing as knowing. Scientists are always trying to learn more and gain a better understanding of the natural world. There are basic methods of gaining knowledge that are common to all of science. At the heart of science is the scientific investigation. A scientific investigation is a systematic approach to answering questions about the physical and natural world. Scientific investigations can be observational —  for example, observing a cell under a microscope and recording detailed descriptions. Other scientific investigations are experimental — for example, treating a cell with a drug while recording changes in the behavior of the cell.

The flow chart below shows the typical steps followed in an experimental scientific investigation. The series of steps shown in the flow chart is frequently referred to as the scientific method. Science textbooks often present this simple, linear “recipe” for a scientific investigation. This is an oversimplification of how science is actually done, but it does highlight the basic plan and purpose of an experimental scientific investigation: testing ideas with evidence. Each of the steps in the flow chart is discussed in greater detail below.

Diagram shows the scientific cycle arranged in a circular formation: Observation, questions, hypothesis, experiment, analysis, conclusion and then returning to observation again.
Figure 1.4.1 The Scientific Method is a never ending cycle.

Science is actually a complex endeavor that cannot be reduced to a single, linear sequence of steps, like the instructions on a package of cake mix. Real science is nonlinear, iterative (repetitive), creative, unpredictable, and exciting. Scientists often undertake the steps of an investigation in a different sequence, or they repeat the same steps many times as they gain more information and develop new ideas. Scientific investigations often raise new questions as old ones are answered. Successive investigations may address the same questions, but at ever deeper levels. Alternatively, an investigation might lead to an unexpected observation that sparks a new question and takes the research in a completely different direction.

Knowing how scientists “do” science can help you in your everyday life, even if you aren’t a scientist. Some steps of the scientific process — such as asking questions and evaluating evidence — can be applied to answering real-life questions and solving practical problems.

Making Observations

A health professional viewing an xray.
Figure 1.4.2 Health professionals use many tools in order to make observations.

Testing an idea typically begins with observations. An observation is anything that is detected through human senses or with instruments or measuring devices that enhance human senses. We usually think of observations as things we see with our eyes, but we can also make observations with our sense of touch, smell, taste, or hearing. In addition, we can extend and improve our own senses with instruments such as thermometers and microscopes. Other instruments can be used to sense things that human senses cannot detect at all, such as ultraviolet light or radio waves.

A black and white photo of Alexander Fleming examining bacterial growth on a petri dish.
Figure 1.4.3 Alexander Fleming examining bacterial growth.

Sometimes, chance observations lead to important scientific discoveries. One such observation was made by the Scottish biologist Alexander Fleming (pictured below) in the 1920s. Fleming’s name may sound familiar to you because he is famous for a major discovery. Fleming had been growing a certain type of bacteria on glass plates in his lab when he noticed that one of the plates was contaminated with mold. On closer examination, Fleming observed that the area around the mold was free of bacteria.

Asking Questions

Observations often lead to interesting questions. This is especially true if the observer is thinking like a scientist. Having scientific training and knowledge is also useful. Relevant background knowledge and logical thinking help make sense of observations so the observer can form particularly salient questions. Fleming, for example, wondered whether the mold — or some substance it produced — had killed bacteria on the plate. Fortunately for us, Fleming didn’t just throw out the mold-contaminated plate. Instead, he investigated his question and in so doing, discovered the antibiotic penicillin.

Hypothesis Formation

Typically, the next step in a scientific investigation is to form a hypothesis. A hypothesis is a possible answer to a scientific question. But it isn’t just any answer. A hypothesis must be based on scientific knowledge. In other words, it shouldn’t be at odds with what is already known about the natural world. A hypothesis also must be logical, and it is beneficial if the hypothesis is relatively simple. In addition, to be useful in science, a hypothesis must be testable and falsifiable. In other words, it must be possible to subject the hypothesis to a test that generates evidence for or against it. It must also be possible to make observations that would disprove the hypothesis if it really is false.

For example, Fleming’s hypothesis might have been: “A particular kind of bacteria growing on a plate will die when exposed to a particular kind of mold.” The hypothesis is logical and based directly on observations. The hypothesis is also simple, involving just one type each of mold and bacteria growing on a plate. In addition, hypotheses are subject to “if/then” conditions. Thus, Fleming might have stated, “If a certain type of mold is introduced to a particular kind of bacteria growing on a plate, then the bacteria will die.” This makes the hypothesis easy to test and ensures that it is falsifiable. If the bacteria were to grow in the presence of the mold, it would disprove the hypothesis (assuming the hypothesis is really false).

Hypothesis Testing

Hypothesis testing is at the heart of the scientific method. How would Fleming test his hypothesis? He would gather relevant data as evidence. Evidence is any type of data that may be used to test a hypothesis. Data (singular, datum) are essentially just observations. The observations may be measurements in an experiment or just something the researcher notices. Testing a hypothesis then involves using the data to answer two basic questions:

  1. If my hypothesis is true, what would I expect to observe?
  2. Does what I actually observe match what I expected to observe?

A hypothesis is supported if the actual observations (data) match the expected observations. A hypothesis is refuted if the actual observations differ from the expected observations.

The scientific method is employed by scientists around the world, but it is not always conducted in the order above. Sometimes, hypothesis are formulated before observations are collected; sometimes observations are made before hypothesis are created. Regardless, it is important that scientists record their procedures carefully, allowing others to reproduce and verify the experimental data and results. After many experiments provide results supporting a hypothesis, the hypothesis becomes a theory. Theories remain theories forever, and are constantly being retested with every experiment and observation. Theories can never become fact or law.

In science, a law is a mathematical relationship that exists between observations under a given set of conditions. There is a fundamental difference between observations of the physical world and explanations of the nature of the physical world. Hypotheses and theories are explanations, whereas laws and measurements are observational

1.4 Summary

  • The scientific method consists of making observations, formulating a hypothesis, testing the hypothesis with new observations, making a new hypothesis if the new observations contradict the old hypothesis, or continuing to test the hypothesis if the observations agree.
  • A hypothesis is a tentative explanation that can be tested by further observation.
  • A theory is a hypothesis that has been supported with repeated testing.
  • A scientific law is a statement that summarizes the results of many observations.
  • Experimental data must be verified by reproduction from other scientists.
  • Theories must agree with all observations made on the phenomenon under study.
  • Theories are continually tested, forever.

1.4 Review Questions


1.4 Explore More

How simple ideas lead to scientific discoveries, TED-Ed,  2012.


Figure 1.4.1

The Scientific Method (simple), by Thebiologyprimer on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication license (https://creativecommons.org/publicdomain/zero/1.0/deed.en).

Figure 1.4.2

Anatomy Bone Bones Check Doctor Examine Film, by rawpixel on Pixabay, used under the Pixabay License (https://pixabay.com/de/service/license/).

Figure 1.4.3

Penicillin Past, Present and Future- the Development and Production of Penicillin, England, 1944, by Ministry of Information Photo Division Photographer. This photograph was scanned and released by the Imperial War Museum on the IWM Non Commercial Licence. It is now in the public domain (https://en.wikipedia.org/wiki/Public_domain).


TED-Ed. (2012, Mar 13). How simple ideas lead to scientific discoveries. YouTube. https://www.youtube.com/watch?v=F8UFGu2M2gM

Wikipedia contributors. (2020, July 7). Alexander Fleming. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Alexander_Fleming&oldid=966489433




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