Genetic Variation – Natural Selection

Introduction:

Within a given species, we can identify differences among individuals. Variations can be seen in pictures, words or measurements. In this investigation you will look for variations in several living things.

Objectives:

The student scientist will determine patterns in the living things and be able to measure and record the variations among them. The student scientist will also observe advantages some living things have over the others.

Materials:

Soaked Bean Seeds

Leaves from the same tree or pine needles from the same tree

Millimeter Ruler

Graph Paper

String

Procedure:

1. Bean Seed Differences:

Take 10 soaked seeds and peel off the seed coat so that it may be easily divided in half.

Measure one half of each seed (longest dimension) to the nearest millimeter.

Record you measurements in the table below.

Length in mm.

Pool your data with the other students in the class, so that you have between 50 and 100 measurements.

Determine the number of seeds that have the same length in millimeters. Place this data in the chart below.

Length of seed
Number of that seed type

2. Leaf Differences:

Each group must have 10 leaves from the same species of tree or plant. Measure the length of the leaf from the tip of the blade to the end of the petiole.

Record the measurements in the chart below.

Length in mm.

Pool your data with the other students in the class, so that you have between 50 and 100 measurements – add your data to the data on the whiteboard and the lab computer.

Determine the number of leaves that have the same length in millimeters. Place your data in the chart below.

Length of leaf in mm.
Number of that leaf type

3. Eye Width:

Tie a knot about 2 inches from the end of a piece of string. 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. Stretch the string tightly and mark, with your thumb nail, the point of the outer corner of the other eye.

Measure the distance between the knot and thumb nail to the nearest millimeter. This measurement represents the distance between the 2 corners of your eyes.

Have your partner measure the distance between your eye corners.

Record the data in the space below.

Your eye distance ______Your partners eye distance.______

Pool your data with that of the rest of the class in the chart below.

Length between eyes
Number having that measurement

Results:

Prepare a line graph of each group of pooled data.

Calculate the average length of each of the three items measured.

Summary:

1. In what ways are the three graphs alike?

2. Most of the seed is stored food. Looking at your graph, how many seeds have the most reserve food?

3. What advantage would this have in the development of a newly germinated seed?

4. How might leaf length affect the ability of the plant to produce food?

5. Why do you think desert plants have small leaves?

Graphs:

Calculations of averages: (Average=Total sum of measurements/number of data points measured)

Natural Selection Lab 2