Scientific Method Introduction and Pre Lab Report Use the following virtual activity to practice using the scientific method to answer a question Scientifi

Scientific Method Introduction and Pre Lab Report Use the following virtual activity to practice using the scientific method to answer a question Scientific Method: Introduction and Pre-Lab
Chances are you have studied the steps of the scientific method every year of grade school and are also
studying it now in lecture. Rather than reviewing that material again, we will focus here on applying the
practical elements of the scientific method to real experiments. Our three main topics will be variables,
control experiments, and the hypothesis.
Figure 1: Steps of the Scientific Method (Michael Fullerton Creative Commons 4.0)
1.
2.
3.
4.
5.
6.
Observation
Research Question
Hypothesis
Experimental Design
Collect data
Conclusions (support/reject hypothesis)
VARIABLES
When designing an experiment, there are many different options of how to do things. How much water
you pour in the cup, how long you wait, what you measure, how you measure it, all of these are
variables. The three types of variable are independent, dependent, and control.
The independent variable is the condition you are testing. For example, if you are testing which brand of
dog food dogs like best, the independent variable is the different brands of dog food. If you are testing
which brand of fertilizer works best, the independent variable is the different types of fertilizer. Another
way to recognize this variable is that this is the condition you are “changing on purpose” between each
experiment. The independent variable is also called the experimental variable.
The dependent variable is the data you are taking on your experiment. This is the information you will
use to make your conclusions later. If you are testing which brand of dog food dogs like best, the
dependent variable might be how much of each brand the dogs eat, or possibly which of the brands the
dog eats first. If you are testing which brand of fertilizer works best, the dependent variable might be
how tall each plant grows or how much fruit they produce. Another way to recognize this variable is that
this is the value that you think will change based on the changes you make to the independent variable.
You think that this value “depends” on the condition you are testing.
The control variables are elements of the experiment that you take deliberate action to keep the same.
Back to our dog food test, putting the same amount of food in each bowl is a control variable. In the
plant experiment, giving the plants the same amount of water is an important control variable. Things
that stay the same without you taking deliberate action do not count as control variables. Essentially, if
you don’t identify them ahead of time, they are not control variables. Also, control variables are usually
things you think might alter the outcome of the experiment. You can’t control everything, so you have to
focus on those things that you think are actually important.
Most of the errors made when designing or reporting on experiments involve the three types of
variables. Sometimes a second independent variable sneaks into the experiment. This is usually
something that should have been a control variable, but the experimenter didn’t pay attention to it. In
the plant fertilizer experiment, if some fertilizers are liquid and others are solid, the plants receiving the
liquid fertilizer are also receiving more water. This is because the fertilizer is dissolved in water. The total
amount of water must be adjusted for these plants so that you aren’t accidentally making water amount
an independent variable.
Another common error is failing to plan out the dependent variable. In our dog food experiment, failing
to define what “better” means ahead of time can cause problems. When putting out three types of dog
food at the same time, is better defined by which food the dog eats first or which one the dog eats the
most of?
One final common cause of error is waiting until the end of an experiment to name the control variables,
then choosing things which were coincidentally the same. In our plant fertilizer experiment, you
shouldn’t list “room temperature” as a control variable. True, the plants were all grown at the same
temperature because they were in the same room, but you didn’t take deliberate action to make this so.
Experiment Note – For every experiment you do, you will be required to identify all three types of
variables before you begin the experiment.
CONTROL EXPERIMENTS
Control experiments are used to set the baseline for your experiments and also to make sure your
measurement for the dependent variable works. The negative control lets you know the
value of the independent variable without treatment. In our plant fertilizer experiment, a plant with no
fertilizer serves as the negative control. This lets you know how much a plant should grow on its own.
The negative control is also sometimes called the control group. When testing the effectiveness of any
treatment, the group that does not receive the treatment is called the control group. A positive control
lets you know that your basic experiment conditions are valid. In the plant experiment, the plant
without fertilizer also serves as a positive control. If it doesn’t grow at all, you know there is a problem
with your setup and none of your fertilizer results will be useful. Some experiments do not have control
experiments. Our dog food experiment might not have any.
These positive and negative control experiments have nothing to do with control variables. The fact that
they both contain the word “control” is a coincidence.
HYPOTHESIS
A hypothesis is a statement about the results of an experiment made before the experiment is
performed. It is a prediction of the outcome based on what you already know. A good hypothesis usually
includes the dependent and independent variables. For example, “When given the choice between
three kinds of dog food, dogs will eat more of the Purina than of Kibbles and Bits or Kroger brand,”
names the independent variable (kinds of dog food), the independent variable (how much is eaten), and
a prediction of the outcome.
A common mistake in making a hypothesis is making a question. “Which fertilizer works best?” is not a
hypothesis. “Truegreen works better than Vigoro,” is a hypothesis. A better hypothesis would be, “Plants
given Truegreen fertilizer grow taller than plants given Vigoro.” This hypothesis is better because it
includes our variables.
Another common mistake is naming an independent variable that can’t actually be tested. For example,
our hypothesis about dog food should never be, ” . . . dogs will like Purina better than Kibbles and Bits or
Kroger brand.” You cannot tell what a dog “likes.” You can only say what the dog does; it eats more of
Purina than the others. You can later infer something about likes or dislikes, but that is not actually what
you are testing. If your hypothesis includes words about mental state (likes, hates, loves, wants to, etc.),
it is usually not testable.
Experiment Note – For every experiment you do, you will be required to state the hypothesis before you
begin the experiment.
LEARNING GOALS
By the end of this unit, you should be able to do the following:
1. Describe the steps of the Scientific Method.
2. Define dependent and independent variables.
3. Write a testable hypothesis.
4. Describe the meaning and purpose of experimental controls.
5. Gather data from an experiment and analyze the results.
6. Determine whether data support or reject the experimental hypothesis.
Scientific Method Virtual Lab Activity and Questions
Use the following virtual activity to practice using the scientific method to answer a question.
http://www.biologycorner.com/worksheets/scientific_method_plant_exp.html#.U1p4L_ldXjJ
1. What was the horticulturalist’s observation that led to the plant growth experiment?
2. What is your hypothesis concerning plant growth?
3. What is the independent (experimental) variable?
4. What is the dependent variable?
5. What aspects (variables) of the experiment should you control?
6. Fill in the table with your lab results.
Group
Flower
(control or
species
experimental)
Pot type
Soil brand
Detergent
(yes/no)
Plant 1
Height
(cm)
Plant 2
Height
(cm)
Average
height
(cm)
Plant 2
Height
(cm)
Average
height
(cm)
7. What is your conclusion?
REPEAT this experiment but choose a DIFFERENT independent variable.
1. What is your new independent variable?
2. What is your new hypothesis
3. Fill in the table with your lab results.
Group
Flower
(control or
species
experimental)
Pot type
Soil brand
Detergent
(yes/no)
Plant 1
Height
(cm)
4. Write out your results in words. Use the average plant heights in your statement.

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