Smith Name ______________________________
Biology
Page 1
Graphing Review
Introduction
Line graphs compare two variables. Each variable is plotted along an axis. A line graph has a vertical axis and a
horizontal axis. For example, if you wanted to graph the height of a ball after you have thrown it, you would put time
along the horizontal, or x-axis, and height along the vertical, or y-axis.
Line graphs are important in science for several reasons such as:
showing specific values of data. If one variable is known, the other can be determined.
showing trends and relationships in data clearly. They visibly depict how one variable is affected by the other as
it increases or decreases.
allowing the viewer to make predictions within recorded data, called interpolation, and to make predictions
about data not yet recorded, called extrapolation.
Interpolation vs. Extrapolation
Determine which of the examples below is interpolation and which is extrapolation. Explain why.
1. The value of Sarah’s car in 2004 was $17,500. ______________________________________________________
2. The value of Sarah’s car in 2008 was $1,900. _______________________________________________________
How to Construct a Line Graph:
1. Identify the Variables & Label the Axes
a. Independent Variable – factor that is varied in an experiment and specifically controlled by the
experimenter
i. Label along the x-axis (horizontal) – include units
ii. Typically found on the left side of a data table
b. Dependent Variable – factor that is measured in an experiment and will change as a result of the
independent variable
i. Label along the y-axis (vertical) – include units
ii. Typically found on the right side of a data table
2. Determine the Graph Scale
a. Determine the magnitude (numeric value) of each variable
b. Establish a scale that best fits the range of each variable
c. Spread the graph to use the MOST available space (use at least ¾ of the graph)
d. Be consistent throughout each axes’ scale
3. Plot the data points
a. Plot each data value on the graph with a dot
b. If multiple sets of data are being plotted, use different colored lines and include a key
Independent vs. Dependent Variable Practice
A student wanted to observe how changing the temperature of the aquarium water would
affect the breathing rate of his goldfish.
o
What is the independent variable? ___________________________________________
o
What is the dependent variable? ____________________________________________
A student wanted to determine how tall corn would grow if different types of fertilizer were
used.
o
What is the independent variable? ___________________________________________
oWhat is the dependent variable? ____________________________________________
Save this for the entire year!
