Name___________________________
Date __________ Period____ Group____
Investigation 9.1: Variation in Size of Organisms
(attach graph to the back)
Purpose: _______________________________________________________________
______________________________________________________________________
Procedure Part A – Line Graph:
1. Choose an object and measure its length in
millimeters. How “typical” do you think this
object is in terms of its length? Guess how
many millimeters larger the longest object will
be. Then guess how much smaller the smallest
object will be. Record the object’s length and
your two guesses in your data table.
Partner 1 Partner 2
Guess
Guess
Actual
(mm)
(mm)
(mm)
Typical Object
Smallest Object
2. Choose three team members to measure the
Largest Object
objects. The fourth member will record the data.
Using a metric ruler, measure
the length of the other 49 objects
to the nearest millimeter. Record
the measurements in your data table.
Line Graph Data
All Objects
(record in order by
whole mm)
3. Next, group the data into increments of 5 or 10 mm (eg. 0-10 mm, 11-20 mm, etc) and place
tally marks on the data table below. This is called a frequency distribution.
Frequency Distribution Data (Part B)
All Objects (size by
whole mm increments)
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
Tally each object in the
Appropriate column
Totals
Procedure Part B – Histogram
4. On graph paper, label the x axis Length of _______. The size of your largest object will
determine the length of this axis (should start at 0). Divide the axis and label it with a
convenient interval that fits your paper (10 mm, 20 mm, etc).
5. Label the y axis Number of _________. Divide the axis and label it with a convenient interval
that fits your paper (0, 1, 2, 3, etc.)
6. Use the data from the frequency distribution table above
to create a histogram. A histogram is simply a bar graph
with the intervals on the horizontal axis and the
frequency (number of individuals at each interval) on the
vertical axis.
7. Draw a line of best fit through the bars of your
histogram, like this:
Discussion Questions:
1. Is there variation within your population?
2. How close were your guesses about the largest and smallest objects?
a. Do you think that using a small sample of 50 is a good way to predict the
characteristics of a large population? Explain.
3. Calculate the mean of your data. The mean is the sum of all measurements divided by the
number of individuals you measured.
4. Find the median, which is the value for the middle sample, when the values (lengths) are
arranged in order.
5. What is the mode, or high point, on the histogram? The mode is the value that occurs the
most often and would be the highest bar on your histogram.
6. Look at the data and your histogram. What is the difference in length between the longest
and shortest objects in your sample?
7. Given the overall size of the objects, do you think this difference is important?
a. What might be the advantage or disadvantage of being smaller or larger than
average?
8. Would you have noticed the differences if you had not measured the objects?
9. Do you think there would be any size difference if the objects were of different ages or from
different places?
10. When do you think a histogram is better, or more accurate, way to present data than a line
graph?