Performance Benchmark N.8.A.4

Students know how to design and conduct a controlled experiment E/L

Scientific inquiry is defined in the National Science Education Standards (NSES p.23) as “the diverse ways in which scientists study the natural world and propose explanations based on the evidence derived from their work. Scientific inquiry also refers to the activities through which students develop knowledge and understanding of scientific ideas, as well as an understanding of how scientists study the natural world.” Middle school students should develop their ability to do inquiry in science classes. As part of inquiry learning, students should be encouraged to ask questions and design investigations to attempt to answer the questions. However, to be taught to think and work scientifically, they need to learn how to identify questions that can be studied scientifically, to design a study so that the most accurate observations can be made, and then to use evidence from that study to support conclusions. Learning how to design and conduct controlled experiments is a valuable academic tool to help students develop their inquiry skills.

There are many ways to “do” science. Scientists learn from observing, asking questions, using models, and by gathering information, data, and evidence from various sources. All of these methods of science are valuable and students should experience a variety of ways of doing science. When a scientist wants to test a specific concept or the effect of a specific variable, using a laboratory or other physical setting, he/she will often design and execute a controlled experiment. A controlled experiment is one that generally will compare an experimental sample to a control sample. Both experiments are identical except for one “variable” that is changed or tested in the experimental sample. For example, if you wanted to see if a plant grew as well in the dark as it did in the light, you could conduct a controlled experiment that includes growing plants in the dark, and growing plants in the light. To be sure that the light was the only thing that affects the outcome, everything else such as temperature, type and amount of soil, and the amount of water given has to be exactly the same for both groups. Traditionally, students learn about the “Scientific Method” when being taught about controlled experiments. The scientific method, although not always used by scientists, is often included as a fundamental method in textbooks and taught by many teachers as a way to teach about controlled experiments. Teaching students the scientific method is useful because it helps young minds to learn the importance of reasoning and developing systematic ways to solve a problem or answer a question. It also provides a foundation for learning how to conduct a controlled experiment, and helps students organize and plan a scientific study to answer questions about the natural world.

Students however, must also learn that not all science follows the specific, detailed, step-by-step process that is called the scientific method. “The scientific method” is not the only scientific method. Discoveries are made through observations, trial and error, development and use of models, and various other processes and all of these processes must be encouraged.

For further information related to scientific investigations and inquiry see

MS TIPS Benchmark N.8.A.6.

Students need to be challenged to investigate and analyze questions about nature. This requires encouraging them to independently develop tests and experiments on their own, rather than providing them with “cook book” scientific verification labs. They need to learn how to use evidence to support an answer or an explanation. They need to learn how to record and evaluate data and results. Through teaching how to design and conduct controlled experiments, students learn how to identify variables and how to control all the variables in an experiment. Teaching all of these scientific processes and more can be facilitated by incorporating the scientific method. We will therefore look at steps generally included in lessons about the scientific method and controlled experiments. These steps, although not necessarily completed in this specific order, are: observing, questioning, researching and more observing, hypothesizing, experimenting, analyzing, communicating, and questioning further. The scientific method can more accurately be called an “Inquiry Cycle.”

Figure 1. Cyclic nature of scientific investigations.

(From http://www.kerrvilleisd.net/Peterson/HPMS_Science/Documents/Scientific_Method.png)

To read more about how controlled experiments and the scientific method are incorporated into scientific research, see http://www.societyforscience.org/isef/primer/scientific_method.asp .

Controlled Experiments

A controlled experiment is one that generally will compare an experimental sample to a control sample. Both experiments are identical except for one “variable” that is changed or tested in the experimental sample. For example, if you wanted to see if a plant grew as well in the dark as it did in the light, you would run two tests…one with plants in the dark, and the other with plants in the light. Everything else such as temperature and the amount of water given has to be exactly the same for both groups.

Several studies completed by scientists to debunk the idea of abiogenesis provide good examples of controlled experiments and their benefit of supporting scientific hypothesis and testing theories. Aristotle believed life came from non life. Beginning in the 1600’s, several studies ultimately led to the rejection of this theory of spontaneous generation. Francesco Redi used controlled experiments to disprove spontaneous generation. The figure below illustrates his controlled experiment. The only difference between the experimental samples was whether or not flies could directly access the meat. His conclusion was that maggots do not spontaneously appear out of meat, but rather they come from flies.

Figure 2. Redi’s controlled experiment illustration.

(From http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap1.html)

Other scientists conducted controlled experiments that supported the hypothesis that life only comes from other life and does not spontaneously appear, Pasteur’s (1800’s) experiments provided strong evidence that life arose from other life. In this classic experiment, all conditions were the same for all flasks used, except for the exposure to particles in the air.

Figure 3. Illustration representing Pasteur’s study was retrieved.

(From http://www.microbiologybytes.com/introduction/History.html)

To read more about the scientific studies disproving spontaneous generation see

http://microbiology.suite101.com/article.cfm/spontaneous_generation

These and other experiments were early examples of controlled experiments. They were repeated many times, and only one variable was altered.

Let’s look now at specific steps used to design and implement a controlled experiment. There are many resources in text books and on line that discuss the various steps of the scientific method, which as discussed earlier is not the only method of science, but does serve as a tool that can be used to teach about controlled experiments.

Designing a Controlled Experiment Requires Identifying a Problem or a Question

By observing the natural world, students can identify questions. In order for a question to be studied in a controlled experiment, it needs to be something that can be tested scientifically. It should be specific and limited. It should also be open ended, and not able to be answered with a simple yes or no.

For further discussion of a Problem visit http://school.discoveryeducation.com/sciencefaircentral/scifairstudio/handbook/scientificmethod.html

Hypothesis is Identified Before an Experiment is Designed

Prediction can be used as a hypothesis. Some texts define a hypothesis as an “educated guess”. While this is partially true, we have to be careful to teach students that it is much more than a guess. Rather, a hypothesis is a possible answer to the question, and is based on what is known or understood. A scientific hypothesis should be testable, measurable, specific, and clearly understood.

To learn more about what a hypothesis is or should be, see

http://www.batesville.k12.in.us/Physics/PhyNet/AboutScience/Hypotheses.html

http://sci.waikato.ac.nz/evolution/Theories.shtml

Experimental results may either support or not support a hypothesis. When results do not support a hypothesis, the hypothesis should not be called “wrong.” Instead, it can be said that the hypothesis is not supported based on evidence. When that occurs, the hypothesis could be reformulated based on observations and another controlled experiment to test the new hypothesis could be designed. A theory is a hypothesis that is supported after many tests.

Plan a Controlled Experiment

Designing a controlled experiment takes practice and time. The experiment must be replicable, have sufficient sample sizes, and needs to be designed so that only the variable being tested varies. A reliable acceptable controlled experiment is sometimes called a “Fair test” which is one in which only one factor at a time is changed while all other conditions are kept constant. When designing a controlled experiment, step-by-step procedures should be written, all variables need to be clearly identified, and a method of gathering data should be developed.

For additional information on fair tests see

http://www.sciencebuddies.org/science-fair-projects/project_experiment_fair_test.shtml

and http://www.sciencebuddies.org/science-fair-projects/project_experimental_procedure.shtml

Many science fair related sites provide explanations and examples of the scientific method and often times science fair organizers prefer the “traditional” scientific method as a standardized format for entries.

To learn more about science fair and science fair projects visit

Discovery Education http://school.discoveryeducation.com/sciencefaircentral/

Science Stuff.com at http://sciencefairproject.virtualave.net/scientific_method.htm

Science Buddies at http://www.sciencebuddies.org/

To learn more about how to choose and use appropriate laboratory equipment and tools refer to MS TIPS Benchmark N.8.A.5

Controls and Variables

A crucial part of designing a controlled experiment is to identify the variable to be tested and the controls needed to assure that results are due to the variable being tested and not other conditions or influences.

Variable is the treatment or condition that is to be tested. In a controlled experiment, the variable is the only thing that should be different between different experimental set ups. Some texts describe both the independent and dependent variable, but it is not necessary to teach middle school students that vocabulary. The important thing to help these students is to help them learn that in a controlled experiment, only one variable is to be tested, and that everything else in the experiment should remain constant.

Controls are conditions and treatments in a controlled experiment that are kept constant. To determine if that variable affects the outcome of the experiment, a control must also be run which entails the exact same conditions, but without the variable being tested. For example, if we wanted to test the effect of salt water on the growth of plant X, you would water (several samples) of plant X with the same concentration of salt water. The concentration of the salt would remain the same throughout the experiment as would other conditions such as the amount of water, light, temperature, etc. The control would be to run the same experiment using no salt in the water, but keeping everything else the same.

The following chart provides examples of variables and controls. Although middle school students do not need to learn the terms Independent Variable and Dependent Variable, the following table illustrates examples of variables and controls.

Question / Independent Variable
(What I change) / Dependent Variables
(What I observe) / Controlled Variables
(What I keep the same)
How much water flows through a faucet at different openings? / Water faucet opening (closed, half open, fully open) / Amount of water flowing measured in liters per minute / ·  The Faucet
·  Water pressure, or how much the water is "pushing"
"Different water pressure might also cause different amounts of water to flow and different faucets may behave differently, so to insure a fair test I want to keep the water pressure and the faucet the same for each faucet opening that I test."
Does heating a cup of water allow it to dissolve more sugar? / Temperature of the water measured in degrees Centigrade / Amount of sugar that dissolves completely measured in grams / ·  Stirring
·  Type of sugar
"More stirring might also increase the amount of sugar that dissolves and different sugars might dissolve in different amounts, so to insure a fair test I want to keep these variables the same for each cup of water."
Does fertilizer make a plant grow bigger? / Amount of fertilizer measured in grams / 1.  Growth of the plant measured by its height
2.  Growth of the plant measured by the number of leaves
3.  See Measuring Plant Growth for more ways to measure plant growth / ·  Same size pot for each plant
·  Same type of plant in each pot
·  Same type and amount of soil in each pot
·  Same amount of water and light
·  Make measurements of growth for each plant at the same time
"The many variables above can each change how fast a plant grows, so to insure a fair test of the fertilizer, each of them must be kept the same for every pot."
Does an electric motor turn faster if you increase the voltage? / Voltage of the electricity measured in volts / Speed of rotation measured in revolutions per minute (RPMs) / ·  Same motor for every test
·  The motor should be doing the same work for each test (turning the same wheel, propeller or whatever)
"The work that a motor performs has a big impact on its speed, so to insure a fair test I must keep that variable the same."

Table 1. Examples of Variables and Controls

(From: http://www.sciencebuddies.org/science-fair-projects/project_variables.shtml)

For additional information on controls, see

http://www.nationmaster.com/encyclopedia/Control-experiment

Once the decision has been made as to what to test, and an experimental procedure has been developed, the following table from Science Buddies.org can be used as a check list for the experimental design:

What Makes a Good Experimental Procedure? / For a Good Experimental Procedure, You Should Answer "Yes" to Every Question
Have you included a description and size for all experimental and control groups? / Yes / No
Have you included a step-by-step list of all procedures? / Yes / No
Have you described how to the change independent variable and how to measure that change? / Yes / No
Have you explained how to measure the resulting change in the dependent variable or variables? / Yes / No
Have you explained how the controlled variables will be maintained at a constant value? / Yes / No
Have you specified how many times you intend to repeat the experiment (should be at least three times), and is that number of repetitions sufficient to give you reliable data? / Yes / No
The ultimate test: Can another individual duplicate the experiment based on the experimental procedure you have written? / Yes / No
If you are doing an engineering or programming project, have you completed several preliminary designs? / Yes / No

Table 2. Procedure checklist.