Science Skills
Begin by asking which one thing will
be changed during the experiment. In this
case, what is being changed is the amount
of sun each bean plant gets. This is the
independent variable.
The amount that the plants grow
depends on the amount of sun the plants
get. This is the dependent variable in this
experiment. Think about the independent
variable as the thing you change, and the
dependent variable as what happens
because of the change.
Every experiment should have only one
independent variable. If the question were
“How much sun and water do plants
need?” two things would be being studied
at once—sun and water, which would be
confusing. It’s important to change only
one variable at a time.
© iStockphoto.com/Tang Wai
What is a variable? The root word of
variable is vary. When you vary something,
you change it. So variables are things that
can change. In science, there are three
main types of variables: independent,
dependent, and controlled. Let’s think
about variables using the research
question “Does a bean plant grow best
in sun or shade?”
Identify and
Control Variables
The only way to get reliable results
from this experiment is to make sure that
all the other variables stay the same, or
are controlled. For example, you would
need to give the plants the same amount
of water and plant them in the same kind
of soil. If any of the variables besides
sunlight changed, you could not be certain
that the results occurred due to the amount
of sunlight each plant got.
Circle the parts of the picture that show the
independent variable.
© Learning A–Z All rights reserved.
oW
hat is an independent variable?
oW
hat is a dependent variable?
oW
hy is it important that all
variables in an experiment,
except for the independent
variable, are controlled?
www.sciencea-z.com
© iStockphoto.com/Tang Wai
illustration by Cende Hill
Understanding the differences
between the three types of variables will
help make all your science experiments
more successful.