Date: _
Name:
Class:
BIOLOGY:
USING GRAPHING SKILLS
INTRODUCTION:
Recorded data can be plotted on a graph. A graph is a pictorial representation of information recorded in a
data table. It is used to show a relationship between two or more different factors. Two common types of
graphs are line graphs and bar graphs. In this investigation, you will interpret and construct a line graph
and a bar graph.
LINE GRAPHS:
In laboratory experiments, you will usually be controlling one variable and seeing how it affects another
variable. Line graphs can show these relations clearly. For example, you_mighl.perform an experiment in
which you measure the growth of a plant over time to determine the rate of the plant's growth. In this
experiment, you are controlling the time intervals at which the plant height is measured. Therefore, time is
called the independent variable. The height of the plant is the dependent variable. Table 1 gives some
sample data for an experiment to measure the rate of plant growth.
The independent variable is plotted on the x-axis. This axis will be labeled Time (days), and will have
a range from 0 days to 35 days. Be sure to properly label your axis including the units on the values.
The dependent variable is plotted on the >>-axis. This axis will be labeled Plant Height (cm) and will
have a range from 0 cm to 5 cm. Think of your graph as a grid with lines running horizontally from the yaxis, and vertically from the x-axis. To plot a point, find the x (in this example time) value on the x axis.
Follow the vertical line from the x axis until it intersects the horizontal line from the^-axis at the
corresponding >> (in this case height) value. At the intersection of these two lines, place your point.
Figure 1 shows what a line graph of the data in Table 1 might look like.
Table 1 Experimental Data
for Plant Growth versus Time
-Time <days)^Maiit height (cm}^
0
1.43
7
2.16
14
2.67
21
3.25
28
4.04
35
4.67
BAR GRAPHS:
Bar graphs make it easy to compare data quickly. We can see from Figure 4 that Jupiter has the largest
radius, and that Pluto has the smallest radius. We can also quickly arrange the planets in order of size.
Bar graphs can also be used to identify trends, especially trends among differing quantities. Examine
Figure 5 below.
Figure 4
Figure 5
Radii of the Planets
Time Spent on Production Work
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3
The data are represented accurately, but it is not easy to draw conclusions quickly. Remember that when
you are creating a graph, you want the graph to be as clear as possible. If we graph the exact same data on
a graph with slightly different axes, as shown in Figure 6, it may be much easier to draw conclusions.
Figure 6
Time Spent on Production Work
10
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ATM:
To correctly interpret and construct a line graph and a bar graph.
PRE-LAB DISCUSSION:
Read the entire investigation. Then answer the following questions.
1. Would a line graph or a bar graph be better for showing the number of birds of each color in a
population?(l)
Explain why?(1)
2. How could you plot more than one responding variable on a line graph?( 1)
3. Where do you place the manipulated variable on a line graph?(l)
4. Which type of graph would you use to show comparisons?(l)
Explain the reason for your answer.(l)
5. Why is it important to have all parts of a graph clearly labeled and drawn?(l)
Line Graph
PROCEDURE:
Part A. Interpreting Graphs:
1. The type of graph that best shows the relationship between
two variables is the line graph. A line graph has one or more
lines connecting a series of points. See Figure 1. Along the
horizontal axis, or x-axis, you will find the manipulated
variable in the experiment. Along the vertical axis or^-axis,
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Numerical scale
you will find the responding variable.
figure 1
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f.How long did it take for plant 1 to grow 6 cm?
2. Use the line graph in Figure 2 below to answer questions a through f below. (6)
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Time (Days)
Figure 2
3. A bar graph is another way of showing relationships between variables. A bar graph also contains an x-axis
and a ^-axis.
But instead of points, a bar graph uses a series of columns to display„ , .
data. See Figure 3. On some bar graphs, the ^-axis has labels rather than
a numerical scale.
This type of bar graph is used only to show comparisons.
Figaro 3
Red Blood Cell Count During Human Growth
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4. Use the bar graph in Figure 4 (above) to answer questions a through e below. (5)
a.At birth, what is the average number of red blood cells per mm3 of blood?
b.What appears to happen to the number of red blood cells between birth and 2 months?
c What happens to the number of red blood cells between the ages of 6 and 8 years?
d.Between what ages is a human likely to have 4.6 million red blood cells?
e.After 14 years of age, do males or females have a higher red blood cell count?
Part B. Constructing Graphs:
1. When plotting data on a graph, you must decide which variable to place along the jc-axis and
which variable to place along the v-axis. Label the axes of your graph accordingly. Then you
must decide on the scale of each axis; that is, how much each unit along the axis represents. Scales
should be chosen to make the graph as large as possible within the limits of the paper and still include
the largest item of data. If the scale unit is too large, your graph will be cramped into a small area and
will be hard to read and interpret. If the scale unit is too small, the graph will run off the paper. Scale
units should also be selected for ease of locating points on the graph. Multiples of 1. 2. 5. or 10 are
easiest to work with.
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2. Use the information recorded in Data
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DATA TABLE 1: Breathing rate of freshwater Sunfish.
Table 1 to construct a line graph on the
Temperature (C)
Breathing rate (per minute)
plot the data, connect the points, and give your
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graph a title. (10)
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30
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38
23
60
25
57
27
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grid provided below. You should label each
axis, mark an appropriate scale on each axis,
Use 2 small squares = 1C
Use 1 small square = 1 breath per minute.
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3. Use the information recorded in Data Table 2 to construct a bar graph on the grid provided below. You
should label each axis, mark an appropriate scale on each axis, plot the data, darken/color the columns
of the graph, and give your graph a title. (10) (Use 5 small squares = lmonth: 2 small squares = lmL.)
Data Table 2
Month
Jan.
Fell.
15
21
Rainfall |mL|
Mar April May June July Aug. Sept. Oct
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Nw. Dec.
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ID
Average Rainfall in Willamette Valley
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ANALYSIS AND CONCLUSIONS:
1. Comparing and Contrasting: How is a graph similar to a data table?(2)
2. Comparing and Contrasting: How is a line graph different from a bar graph?(2)
3. Using Graphs: Does a steep curve on a line graph indicate a rapid or slow rate of change?(l)
4. Using Graphs: You are conducting an experiment to measure the gain in mass of a young mouse
over a ten-week period. In constructing a graph to represent your data, which variable should you
place along the ^-axis and which variable should you place along the^-axis? (2)
.y-axis
Explain your answer. (4)
5. Using Graphs: What is an advantage of using multiple lines in a line graph? (See Figure 2.) (1)