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Experimental Variables
Different factors that can change during an
experiment are known as variables.
1. Independent Variable
• Is the variable an experimenter can change.
Is Plant Growth Affected by:
Change only 1 variable at a time
2. Dependent Variable
• Is the variable that occurs as a result of the
experimenters’ change.
• Size of the leaves
• Tallness (cm of growth)
Color of leaves
• Number of flower buds
Independent or Dependent?
• 1. You want to see if playing music makes
plants grow taller. What is the dependent
variable in this experiment?
• Plant Height
Independent or Dependent?
• You want to measure the effect of different
amounts of oxygen on the rate of yeast
growth. What is the dependent variable?
• Yeast Growth
Independent or Dependent?
• An entomologist (bug scientist) wants to
determine if temperature changes how many
times a cricket chirps. What is the independent
• Temperature
Independent or Dependent?
• You think that a certain part
of your brain is important in
memory. To test this, you will
remove this part of the brain
from rats and see if they
remember how to get
through the maze. What is
the independent variable in
this experiment?
• Removal of a certain part of
the brain
When Designing an Experiment keep these
in mind!
You change only 1 variable at a time when
experimenting. The rest of the variables you would
1. Control Group
• Contains all the parts of an experiment
EXCEPT the one experimental factor being
• A control is a standard to which you can
compare your results.
2. Experimental Group
• Contains all the factors of the control group
PLUS the one factor that is being tested.
Control & Experimental Group
• Harvester ants often strip a bush of all of its leaves.
Some people believe this helps the plant grow
thicker, healthier stems. In an experiment, a student
stripped off all the leaves from a set of plants. In a
second set of identical plants, the student allowed
ants to strip off the plants’ leaves. In order to
improve this experimental design, it is most
important to add a set of plants that:
Experimental Controls
• When conducting an experiment, these are
the items that NEVER change
– What examples can we use from our Inquiry Lab?
Room temperature
Rate of gravity
Person dropping the ball
Thickness of sand layer
What else???