Experimental Variables. Lake Howell High School BIO 3233

Experimental Variables
What is measured during a controlled experiment?
Why?
When scientists set out to do an experiment, they fi rst think about the variables that may affect the
outcome of the experiment. A variable is any condition that may cause a change in the system being studied. Some variables are measured quantitatively, like temperature, mass or height. Other variables
are recorded in a qualitative manner, like color, texture or species. The most important factor is that the
scientist runs a controlled experiment. In a controlled experiment, only one variable is changed to ensure
that the effect of only that one variable can be measured.
Model 1 – Photosynthesis in an Aquatic Plant
Oxygen gas
1. The diagram in Model 1 illustrates a clipping of an aquatic plant in water.
a. What process is occurring in the plant’s cells to produce the gas in the bubbles that appear?
b. What gas is the plant producing?
c. What source of energy is the plant using to conduct the process recorded in part a?
2. Depending on the environment the plant is in, more or less gas may be produced. Suggest a
method for measuring the rate of gas production from the aquatic plant in Model 1.
3. With your group, create a list of environmental factors that may affect the rate of gas production
in the aquatic plant in Model 1. These factors could become variables in an experiment.