Materials Included In Kit

Additional Materials Required

Safety Precautions

The materials used in this laboratory activity are considered nonhazardous. Remind students that the sunflower seeds are not to be consumed. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

All materials used in this lab may be saved and stored for future use.

Lab Hints

• Enough seeds are provided in this kit for 30 students working in pairs, or for 15 groups of students. Five calipers are included which must be shared among three student groups. Additional calipers may be purchased separately from Flinn Scientific, Catalog No. AB1006.

Answers to Prelab Questions

1. What variables are being studied in the histogram in this activity?

   The two variables studied in this activity are sunflower seed mass and length.

2. Besides grades and seed sizes, what other data sets could be analyzed using a histogram?

   Student answers will vary. Possible answers include population studies regarding height, weight, etc.

Sample Data

Answers to Questions

1. Examine the seed mass data. Group the data into five logical bins based on the range of numbers given. Student answers will vary. Based on the sample data provided five logical bins would be 0.10, 0.12, 0.14, 0.16 and 0.18.
2. Construct a histogram of the seed mass based on the information in the data table above and the answer to Question 1.
   {11060_Answers_Figure_2}
3. Examine the seed length data. Group the data into six logical bins based on the range of numbers given. Student answers will vary. Based on the sample data five logical bins would be 14, 15, 16, 17, 18 and 19.
4. Construct a histogram of the seed length based on the information in the data table above and the answer to Question 3.
   {11060_Answers_Figure_3}
5. Based upon the seed mass histogram, which seed size is the most common in your sample? According to the seed mass histogram it appears that 0.14 and 0.18 g seeds are most common.
6. Based upon the seed length histogram, which seed size is the most common in your sample? According to the seed length histogram it appears that 17–18 mm seeds are most common.
7. A new species of birds is introduced to the area. The bird has a small beak and is unable to eat seeds larger than 17 mm long. How will this new predator affect the distribution of seed size? Will this cause natural selection to occur? If this new species of birds becomes the most abundant species consuming the seeds, it will lead to a shift causing seeds smaller than 17 mm to be selected. However, if this new species only represents 10% of the total population that feeds off the seeds, it may have little affect. If the other 90% can eat seeds of any size, the overall seed population should not shift.

References

Campbell, N. A. Biology; Benjamin Cummings: San Francisco, CA; 2002; 6th Edition, p 595–611.

Introduction

Evolution often conjures mental images of monkeys to cavemen to modern humans today. In reality, evolution can be studied on a much simpler scale. Measure mass and length of sunflower seeds to see how such traits are naturally selected in nature.

Concepts

• Evolutionary adaptations
• Frequency within a population
• Histograms

Background

Land plants are categorized into four main groups—bryophytes, pteridophytes, gymnosperms and angiosperms. Vascular plants, including angiosperms, arose 360 million years ago. The majority of plants found today are angiosperms. Angiosperms are flowering plants, such as sunflowers. The seed contains a plant embryo and food supply surrounded by a protective coat.

The evolutionary history of plants is largely due to their ability to adapt to changing conditions on Earth. The many adaptations of different types of seeds improve their ability to thrive and reproduce in different environments. Animals rely on plants as a food source affects the natural selection of both the plants and the animals. Animals have influenced the evolution of plants and vice versa. One way herbivores help flowering and fruit plants (angiosperms) evolve by carrying and dispersing the pollen and seeds of plants into new environments. In the new area the seed either sprouted or it was unable to develop. New habitats created by this spread of seeds assisted the herbivore as well. If the soil in the new area gradually becomes more salty over time and the seeds and the herbivore adapt to the new conditions, evolution is occurring. Coevolution is the mutual evolutionary influence between two species.

A histogram is a summary graph used to estimate the probability distribution of a variable. In order to make a histogram, data must be collected and sorted into discrete intervals known as bins. A bar is then plotted over each interval representing an area equal to the frequency of the occurrences within the interval. Histograms are a simple graphical means of communicating the distribution of data.

For example, a histogram can be made to show the frequency of grades within a biology class. The class has 30 students— eight students have As (90% or above), 14 students have Bs (80–89%), six students have Cs (70–79%) and two students have less than a C (69% or below). Therefore the bins would be the grades and there would be four bins: 90, 80, 70, 60. Notice the bins are set at equal intervals. The frequency is how many students fall into each bin. See the sample histogram below (see Figure 1).

Experiment Overview

Mass and measure the length of 20 sunflower seeds and construct a histogram to determine the frequency within the sample group.

Materials

Prelab Questions

1. What variables are being studied in the histogram in this activity?
2. Besides grades and seed sizes, what other data sets could be analyzed using a histogram?

Safety Precautions

The materials used in this laboratory activity are considered nonhazardous. So not eat the sunflower seeds. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

1. Obtain 20 sunflower seeds.
2. Using a permanent marker, label each seed 1–20.
3. Using a 0.01-g balance, mass sunflower seed one. Record the mass in the data table on the worksheet.
4. Repeat step 3 using seeds 2–20.
5. Using the calipers, measure the length of seed one to the nearest 0.1 mm. Record the length in the data table on the worksheet.
6. Repeat step 5 using seeds 2–20.
7. Complete the Post-Lab Questions and Calculations on the worksheet.

Student Worksheet PDF

11060_Student1.pdf