Download Natural Selection

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