Name:__________________________
Hour:______
Graphing
Graphing is an important procedure used by scientists to display the data that is collected during a controlled
experiment. Graphs must be constructed correctly to accurately portray the data collected. Many times the wrong
construction of a graph detracts from the acceptance of an individual’s hypothesis.
A graph contains five major parts: a title, the independent variable, the dependent variable, the scales for each
variable recorded on the axis, and a key to the marks, lines, or different types of data.
The title: tells what the graph is about. The name of the graph is important. Nothing “cute” here, it must tell
what the graph is showing. For instance, “Plant growth in centimeters per day for Plant A” is a good title” or
“The Breathing Rate of Goldfish vs. The Temperature of Water” are both acceptable titles. “How big is my
plant?” is not a good title. Titles are typically written as “Y-axis variable” vs. “X-axis variable” and are written at
the top of the graph.
Axis (Axes plural): There are two of these: the X-axis (which is the horizontal axis) and the Y-axis, which is the
vertical axis. The independent variable is put on the x axis and includes such things as temperature, time, or
depth etc. while the dependent variable is put on the y-axis and includes what happens because of the
independent variable.
Data points: these are the actual points that you represent on the graph.
The Independent Variable: is the variable that can be controlled by the experimenter. It usually includes time
(dates, minutes, hours), depth (feet, meters), temperature (degrees Celsius). It is ALWAYS placed on the X axis
(horizontal axis). Typically found on the left side of a data table.
The Dependent Variable: is the variable that is directly affected by the independent variable. It is the result of
what happens because of the independent variable. Example: How many bubbles are produced in an enzyme
reaction?… What is the volume of gas generated by a plant in one hour?, etc… The bubbles are dependent on
the rate of reaction, the volume of gas is dependent on the intensity of light. This variable is placed on the Y-axis
or vertical axis. Typically found on the right side of a data table
The Scales for each Variable: In constructing a graph you need to know where to plot the points represented by
the data that you collected. In order to do this, you must engineer your scale so that it will include all the data
points.
Types of Line Graphs
b.
a.
c.
1. Best fit Straight Line
.
a. Direct Relationship – Both variables increase together
b. Indirect Relationship – As one variable increases, the other decreases
c. Constant Relationship – Change in one variable has no effect on the other
2. Best fit Curved Line
3. Best fit Peak Line
How to Construct a Graph
1. Be certain you know what kind of graph you need. Traditionally, line graphs are used in scientific situations,
but occasionally we also use pie charts, bar graphs, and sometimes even a histogram. (We will be focusing on
line graphs only)
2. Identify the variables and 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
3. Determine graph scale.
a. Establish a scale that best fits the range of each variable
i. Play the “range game” Find the highest value for your data set and then count the available
spaces on the appropriate axis. Think about this one… if you have 30 spaces on your graph and
your data goes to 28, you can safely assume that each “box” has a value of “1” for that data set.
However, if you only have 15 spaces, it is safe to assume that each box has a value of “2”.
Practice will help you to understand this.
b. Spread the graph to use the MOST available space (use at least ¾ of the graph)
i. Use the “75% rule” That is, if your graph doesn’t cover nearly 3/4 of the graph paper, take a
look at your axes again. In general, the graph should be as large as possible, thus making the
data points easy to read. Do not, however, extend your graph beyond the limits of the graph
paper provided.
c. Be consistent throughout each axes’ scale
4. 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
c. COMMON MISTAKE: Some students think that their points MUST be on a line. This is not true.
Sometimes you need to estimate where the points will fall in between the lines. Putting a point here is
fine.
5. Title the Graph
a. Titles are used to clearly portray what the graph is about so be specific.
b. Titles are typically written as “Y-axis variable” vs. “X-axis variable” and are written at the top of the
graph.
Graphing Practice
Independent vs. Dependent Variable
1. A student wanted to observe how changing the temperature of the aquarium water would affect the breathing
rate of his goldfish.
a. What is the independent variable? ___________________________________________
b. What is the dependent variable? ____________________________________________
2. A student wanted to determine how tall corn would grow if different types of fertilizer were used.
a. What is the independent variable? ___________________________________________
b. What is the dependent variable? ____________________________________________
Practice Problem #1
Background: The thickness of the annual rings indicates what type of environmental situation was occurring the time of
the tree’s development. A thin ring usually indicates a rough period of development such as lack of water, forest fires, or
insect infestation. On the other hand, a thick ring means a prosperous period of development. Use the information from
the data table below to create a proper scientific graph and to answer the corresponding questions. Graph on a
separate sheet of graph paper, be sure to number it.
1. What is the dependent variable?_____________________________________________________________________
2. What is the independent variable? ___________________________________________________________________
3. What was the mean thickness of annual rings for 40 year old trees in Forest A? _______________________________
5. What was the mean thickness of annual rings for all trees found in Forest B? _________________________________
6. Based on the data shown, what can be concluded about the comparative health of Forest A & B? _________________
__________________________________________________________________________________________________
7. What type of relationship (constant, direct, or indirect) exists between the age of trees and the average thickness of
the tree’s rings? Explain. ______________________________________________________________________________
__________________________________________________________________________________________________
Practice Problem #2
Background: Clams were placed into various temperatures of water. Use the information in the data table below in
order to create a proper scientific graph and to answer the corresponding questions. Graph on a separate sheet of graph
paper, be sure to number it.
1. What is the dependent variable? ________________________________________________________________
2. What is the independent variable? _______________________________________________________________
3. What is the optimum temperature for clam development? ___________________________________________
4. What is the mean number of clams per sample? ____________________________________________________
5. Approximately how many clams would be developing in 10 degree Celsius water? _________________________
Practice Problem #3
Background: Natalie sets out to run 15 kilometers. Every 30 minutes she checked her pedometer to determine how far
she had run. Use the data below to create a proper scientific graph and to answer the corresponding questions.
1. What is the dependent variable? ________________________________________________________________
2. What is the independent variable? _______________________________________________________________
3. How many kilometers had Natalie run after 40 minutes? _____________________________________________
4. What was Natalie’s average speed (in kilometers per hour) over the course of her run? ____________________
Use the formula Speed = Distance / Time
Practice Problem #4
Background: Match each story on the left with the graph it represents on the right. Each graph compares the distance a
car is from home compared to time.
____1. I had just left home when I realized I had
forgotten my books, so I went back to pick them up.
____2. The battery on my electric car started to run
down.
____3. Things went fine until I had a flat tire.
____4. I started out calmly, but sped up when I
realized I was going to be late.
Practice Problem #5
Background: The pie chart shows the approximate percentages teenagers spend doing various activities in a day. Use the
information in the pie chart to answer the questions below.
1. What percent of the day is spent watching TV? _______
2. How many hours are spent sleeping? _______
3. What activity takes up the least amount of time? __________
4. What activity takes up a quarter of the day? __________
5. What two activities take up 50% of the day? __________
6. What two activities take up 25% of the day? __________
Practice Problem #6
1. What is the dependent variable? ____________________
2. Does the price per bushel always increase with demand?
________________________________________
3. What is the quantity demanded when the price is $5 per bushel?
________________________________________
4. What is the price per bushel when the quantity demanded is 80?
________________________________________
Practice Problem #7
Background: The rate of respiration of a freshwater sunfish was determined at different temperatures. The rate of
respiration was determined by counting the number of times the gill covers of the fish opened and closed during 1minute intervals at the various temperatures. Use the information in the data table below in order to create a proper
scientific graph and to answer the corresponding questions. Graph on a separate sheet of graph paper, be sure to
number it.
_____1. According to the data, as the temperature increases, the rate of respiration of the sunfish
a)
b)
c)
d)
increases steadily
decreases steadily
increases, then decreases
decreases, then increases
_____2. Which title is appropriate for this graph?
a)
b)
c)
d)
The Effect of Temperature on Rate of Respiration in Sunfish
The Effect of Gill Movement on Rate of Respiration in Sunfish
The Relationship Between Temperature and Dissolved Oxygen
The Relationship Between Sunfish Population and Temperature Change in Freshwater Habitats
Practice Problem #8
Background: The data table shows water temperatures at various depths in an ocean.
3. State the general relationship between temperature and water depth.
_____4. The approximate water temperature at a depth of 125 meters would be
closest to
a) 15°C
c) 8°C
b) 13°C
d) 3°C