Variations in Species
Purpose:
1. To observe and measure variations in species using lima bean length, grasshopper femur
length, and human eye width as example 1
2. To construct line graphs representing all variations in bean length, femur length, and eye
width.
3. To calculate and plot the following values for each graph
a. Mean – the average number
b. Median – the middle number (the value with the same # of items above and below it)
c. Mode – the most frequent number
Notes on Calculations:
1. Mean (average) – Multiply the frequency by length for each frequency; add these products
together and divide by total number of specimens
Example:
mm
2
3
4
5
#
1
2
3
1
Mean = (2 × 1) + (3 × 2) + (4 × 3) + (5 × 1) = 25
25/7=3.6
2. Median – Divide the total number of items by 2, call this number “n”.
Find which measurement (starting with least) contains the “n” term. This value is the
median.
3. Mode – The value with the highest frequency
Variations in Species
I. Introduction
The differences by which individuals within a species are identified are known as variations. It
is possible to describe these differences in pictures, words or measurements. Probably the best
description is made in term of measurements.
In this investigation you are going to look for differences in a number of living things, to see if
there is any pattern to these variations. You will also be asked to think about the survival advantages
of some of the variations that you measure.
Materials:
Bean seeds, grasshoppers, millimeter rules, petri dishes, graph paper, string.
II. Materials and Methods
A. Variations in bean seed length. (Table 1)
1. Lay a lima bean seed on a millimeter ruler and measure the longest
dimension of the seed, to the nearest whole millimeter. Repeat until you
have measured 25 seeds.
2. Record all measurements in a table, showing the number of seeds with the
same length.
3. Record your group data in the Class Data Table and in Section III.
(RESULTS)
B. Grasshopper Femur (Table 2)
1. Measure the length of the femur of the jumping leg of several grasshoppers.
DO NOT REMOVE THE LEG. Figure 12-A-1 will help you locate the femur.
2. Record your measurements (mm) in individual data records.
3. Record your group data with Class Data Table for Section III. (RESULTS)
C. Eye Width
1. Tie a knot about 5 centimeters from the end of a piece of string to mark a
point of reference. While holding the string across the bridge of your
partner’s nose, position the knot in the string at the exact outer corner of
one eye.
2. Stretch the string tightly and mark with your thumbnail the point of the outer
corner of the other eye.
3. Measure the distance between the knot and your thumbnail, to the nearest
millimeter. This measurement represents the distance from the corner of
one eye to the corner of the other eye.
4. Have your partner measure this distance on you.
5. Record these measurements in individual data records.
6. Record your group data with Class Data Table and Section III (RESULTS)
Directions for Completing Lab Assignment
1. Prepare a graph of each Class Data Tables to show the distribution of variations. (3 separate
graphs)
2. Plot the range of measurements on the horizontal axis of the graph and the number of
individuals having this measurement on the vertical axis. (See Fig. 12-A-2)
3. Draw a smooth line (without angles) connecting or passing near the dots plotted on each
graph. Each set of measurements must be on a separate graph.
4. Calculate and plot the following values for each graph:
a. Mean – average number; the average length in each set of data.
b. Median – the middle number; the number with the same # of items above and below it.
c. Mode – the most common number.
5. Refer to lab notes for directions (examples) on how to calculate mean, median, and mode.
6. To plot mean, median, mode, draw a line from each on the graph line to that number on the
horizontal axis.
III. Results (3 graphs)
1. Prepare one graph for each Class Data Table
2. Table I – Variations in Bean Length
Table II – Variations in Grasshopper Femur Length
Table III – Variations in Human Eye Width
3. Write a title for each graph. Label each axis for each graph.
4. Write a summary and Conclusion for each graph. (Ex. 52% of beans measured 25 mm, 24%
measured 23 mm, 24% measured 22 mm) ( A conclusion is one sentence with summarizes all
the data)
Class Data Tables
(These are for your own records – do not turn in with data sheets.)
Table 1 – Bean Length
mm
#
Table 1 con’t
mm
#
Total
____________
Total
____________
Table II – Femur Length
mm
#
Table III – Eye Width
mm
#
Table III cont’d
mm
#
Total ____________
Data Sheet
1. In what ways are the 3 graphs alike? __________________________________________
How do they differ?_________________________________________________________
2. The 2 large halves of the seed are modified leaves containing stored food which will be used
by the young plant as it grows. Which of the seeds that you measured would have the most
stored food? _________________________________________________________________
______________________________________________________________________________
3. How does the large seed size help the young plant to survive? _________________________
______________________________________________________________________________
4. Assuming that a grasshopper with a longer femur can jump farther, how might leg length be an
adaptation ( + survival factor) in the life of a grasshopper? _________________________
_____________________________________________________________________________
Can you think of any disadvantages? ________________________________________________
5. What kid of measurement other than length would give a better answer to question 2?
___________________________________________________________________________
IV. Summary and Conclusion
1. Write a brief summary of the Data from Class Tables I, II, III below each graph. (Write the
conclusion in quantitative terms – for example, 52% of beans measured 25 mm, 24%
measured 23 mm, 24% measured 22 mm. Try to account for at least 90% of all the data in
your quantitative conclusion.)
2. Be sure to write a title for each graph
3. Staple graphs to data sheet questions
a. Graph I – Bean Length
b. Graph II – Grasshopper Femur Length
c. Graph III – Human Eye Width