When You Have Completed This Activity, You Should Be Able To

VARIATION LAB

A species is one kind of organism.Members of a species are very similar. All human beings are the same species, as are all dogs.Two plants or animals belong to the same species if they are able to mate and produce fertile offspring.A German shepherd dog and a collie, for example, belong to the same species because they are able to mate to produce offspring that in turn are able to reproduce.Members of the same species have the same number of chromosomes, and the genes are arranged in corresponding positions on them.

In spite of these similarities, variations occur within a species.It is possible to describe these differences in pictures, words, or measurements.In this activity, you will measure some differences that exist among the same species of plants and animals.

Objectives

When you have completed this activity, you should be able to:

demonstrate that variations occur within a species.
construct a bar graph to show variations.
state a rule to show how physical variations are distributed within a group.
explain how physical variation may play an important role in natural selection.

Materials

metric rule
graph paper or graphing calculator
unshelled peanuts
peas or beans

Procedure

Peel the outer covering (seed coat) from the pea or bean seed so that it may be easily divided in half.Lay one of the halves of the seed on the millimeter ruler and determine to the nearest whole millimeter the longest dimension of the seed.Discard both halves.Repeat with other pea or bean seeds until you have measurements from about 100 seeds.Record all measurements in a chart on your own piece of paper.

Place measurements for the pea or bean seed in the following chartshowing the number of seeds with the same length.

Length of seed

Measurement (mm)
Frequency

5.On a piece of graph paper, construct a dot plot from your measurement data.Use the y-axis (vertical) to represent the frequency data points and the x-axis (horizontal) to represent the measurement data points.

6.Connect the dots to obtain a curve.

7. Repeat the above procedures with the unshelled peanuts, except do not remove the shell. Measure the peanut shell’s length from one end to the other using the millimeter ruler and determine the nearest whole millimeter. Repeat, taking measurements with about 100 peanuts. Record all measurements in a chart on your own piece of paper.

8. Place measurements for the peanuts in the following chart showing the number of shells with the same length.

Length of peanut

Measurement (mm)
Frequency

9. On another piece of graph paper, construct a dot plot from your measurement data.Use the y-axis (vertical) to represent the frequency data points and the x-axis (horizontal) to represent the measurement data points.

10. Connect the dots to obtain a curve.

Analysis

1.Compare your two graphs.

How are they similar?

How are they different?

2.How would you describe the curve of the graphs?

3.Is it normal for variation to occur within a group?Explain.

4.Cite two reasons for variations that occur within a group.

5.The two large halves of the seed are modified leaves containing stored food that will be used by the young plant as it grows.Which of the seeds that you measured would have the most stored food?

6.How does large seed size help the young plant survive?

7.What benefits do you think the larger peanuts would have over the smaller peanuts?

8.Write a summary of this activity stating how variation within a species as measured by you is a result of genetic differences within a species.