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Designer Seeds

Frank Taylor



Type of Activity:

  • Hands-on activity
  • Inquiry lab
  • Group learning

Target Audience:

  • Life Science
  • Biology
  • Environmental Studies

What question does this lab/activity help students address?

  • This lesson can be incorporated into a unit studying ecology, plants, seed dispersal, or evolution of plant traits. It addresses seed dispersal mechanisms as well as elements of experimental design.


Background information

Notes for teacher:

Students enjoy the challenge of the seed structure design component of this activity and become very competitive as they seek to create a seed that will travel farthest. Students will probably ask to redesign their seeds and have another opportunity to test them before you even get a chance to offer this option. Encourage students to try to mimic seeds observed in nature.

Required of students:

Students will gain the necessary content background on seed dispersal through the introductory activities associated with this exercise. If students are familiar with principles of evolution and natural selection they will be able to create a scenario for how the features of their seed might have evolved.

Preparation time needed:

Very little preparation time is needed to set-up this activity. You will need an hour or two to collect seeds and set-up the lab stations for the introductory part of this lab.

Class time needed:

  • 1 class period for introductory examination of seeds.
  • 1 class period for design and testing of student created seeds/structures
  • 1 class period for the second round of testing and discussion of results


Lesson/Activity

Summary/abstract:

In this activity students will examine a variety of seeds, describe them, and determine how they are dispersed. Students will investigate seed dispersal mechanisms. Students, working in pairs, will create and test a wind dispersed seed that they have designed themselves. Students will be limited to using a single piece of white paper, one lima bean to represent a seed, tape and scissors. Seeds will be tested by dropping them in front of a window fan and recording the distance they travel. Repeat trials will be conducted, averages calculated, and class data recorded. Students will examine the features of successful seeds and redesign their seed to try to increase the distance it can be carried by wind. Results will be analyzed and comparisons made to natural phenomena.

Materials needed:

  • A variety of seeds
  • Magnifying glasses or dissecting microscopes
  • 1 box type/window fan
  • 1 meter stick
  • class set of 8 1/2 X 11 paper
  • plastic tape
  • class set of scissors
  • lima beans (dried) (1 per pair of student)


Procedure/Description of Activity/Lesson:

Part A: Introduction

Introduce this lesson by having students examine a variety of seeds and fruits. Set-up twelve or more lab stations. Equip each lab station with a magnifying glass or dissecting microscope as appropriate. Collect seeds from around the school, home, grocery stores, unmowed fence rows or abandoned lots. Choose seeds that display a variety of seed dispersal mechanisms.

Some examples of common seeds and how they are dispersed:
Coconutwater
Jewel Weedmechanical expulsion
Maple seedwind (blade-like structure)
Cedar tree fruitanimals (birds excrete seeds)
Milkweedwind (fine white fibers)
Dandelionwind (parachute-like structure)
Grasseswind (light weight)
Burdock (burs)animals (hooks stick to fur)

At each lab station ask students to observe each seed/fruit:

  1. Describe its features
  2. Sketch a diagram of the seed
  3. Label significant parts or features
  4. Speculate on how the seed is transported and explain what observations were used to make this conclusion.
Students will rotate from lab station to lab station.

Part B: Analysis

After students have completed the above activity, discuss with the class their findings and conclusions. Next ask students to consider the following questions. This might be an appropriate homework assignment.

  1. Why is it important, for the survival of a particular plant species, for seeds to be dispersed?
  2. What would happen to the plant species if seeds were not dispersed?
  3. Make a chart listing ways seeds are dispersed. Consider your findings from lab and class discussion. Use your text and any other available resources to make as complete a list as possible.
Review/discuss the above questions after students have had an opportunity to write answers to them.

Part C: Seed Design

Present the students with the following challenge:

Working with a partner, design a wind dispersed seed structure that will carry a single seed(dried lima bean) the farthest distance possible . You will be given one sheet of white 8 1/2 by 11 paper, a pair of scissors, plastic tape, and a one seed. You may not use more than one sheet of paper but you do not have to use all the paper. You may cut, fold, tear, and/or tape your paper in any manner you choose provided your seed is fixed to the seed structure and does not fall out. After you have completed the design and assembly of your seed structure, it will be dropped in front of a fan, and the distance it travels will be recorded. Each seed/seed structure will be dropped 3 times, and the average distance traveled for the three trials will be calculated.

State the problem and write a hypothesis for this experiment. Identify the constants, independent variable, and dependent variable in this experiment.

Testing Seeds:

Place a square window fan on the floor and clear a space in front of the fan about 8 meters long and as wide as the fan. Measure and mark off, with pieces of masking tape, 100 centimeter increments from the fan. Establish a consistent procedure for dropping the seeds in front of the fan. (E.g. All students should drop their seed from a point 30 centimeters in front of the fan and 30 centimeters above it.) Establish a length of time for each trial (E.g. 10 seconds) then mark and measure. Put a data table on the blackboard, listing the student names, trials 1, 2, 3, and the average for the 3 trials.

After all students have had the opportunity to test their seed/seed structure, lead a class discussion examining the data and the seeds.

  • Which seeds traveled the farthest?
  • What were the features of the seeds that traveled farthest?
  • Did the structures of the seeds that traveled the farthest appear similar to structures found in nature?
  • Which student-made seeds had features of wind dispersed seeds found in nature?
  • What seeds did they mimic?
  • Consider your own seed. What could you change that might make your seed travel farther?

Finally, ask students to do the following:

  • Write a new hypothesis, make your changes and test your seed again.

Ask students to respond to the following questions:

  • Compare your data from the first design with your second design. Evaluate your results.
  • How was this experiment similar to what might occur in nature?
  • How was this experiment different from what occurs in nature?
  • What other variables in the natural environment will affect how far a seed travels from the parent plant?
  • Optional student analysis question: If your students have studied principles of evolution, ask them to create a scenario explaining how the seed structure they designed could have evolved by natural selection.


Method of Evaluation:

Student learning can be evaluated through their responses in oral discussion and/or their written analysis. Students could hand in a formal laboratory report based on their work. Alternatively, you may wish to ask students to write a summary of what they did in this activity and what they learned.

Extension/Reinforcement:

  1. Do the same experiment as described above but instead of placing the fan indoors, place the fan outdoors in the grass and test the student designed seeds again. How do the results compare? Did changing the surface that the seeds fall on change the overall results? How might you redesign your seed to travel farther under these new experimental conditions?
  2. Make a collection of seeds found outdoors. Make a poster display. Research how the seeds are dispersed.
  3. Collect a wind dispersed seed found locally. Design an experiment to study the effect of manipulating the seed structure that captures the wind. (E.g. Maples seeds: Remove 1/4, 1/2 and 3/4 of the blade of the seed. Drop the seeds in front of a fan and measure the distance they travel. Do repeat trials.)
  4. Collect wind dispersed seeds from a variety of different local plants. Design an experiment to determine which seeds travel farthest. Analyze your results.


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