Seed Bomb Catapult

Overview:

Plants disperse seeds in a variety of ways, including by catapult or explosion method. In this experiment, students will explore how and why plants disperse seeds in this fascinating method. Students will build and test catapult models to explore seed dispersal and what plant features are ideal for catapult design. Optionally, students can also have the opportunity to catapult actual seeds to grow.

Time: 

25-30min

Lesson Materials:

*You can use the document in the link below to either: tailor the experiment to your needs or to have a printable version of this lesson plan*

Seed Bomb Catapult Lesson Plan

The plan is editable and printable. Copy the Google Doc in your own drive and make edits or you can just print.

Seed Bomb Catapult Lesson Video:

Learning Objectives:

  1. Build catapults.
  2. Hypothesize which catapult will allow for the seed to travel farther away.
  3. Test how seeds are capable of traveling far distances in nature. 
  4. Explain the concept on how plants populate and reproduce in the environment. 
  5. Identify the importance of seeds traveling away from the parent plant.
  6. Observe and test how seed dispersal works using a catapult.

Materials Needed:

Material List per Student

  • 10 Jumbo popsicle sticks
  • 20 regular popsicle sticks
  • 20 rubber bands
  • Cotton balls or pom poms to test the designs
  • 3 seed bombs to catapult into a garden

Alternative Materials

  • Long soda spoon
  • 2 Regular spoons
  • Ruler
  • 1 Corck 
  • Tape
  • Optional: wax paper to help distribute strips of tape

Experimental Methods:

Part 1. Instruction

  1. Learn about native plants and animals that are local to the area.
  2. Discuss the variety of plant dispersal methods. 

Part 2. Introduction to the Project

  1. Students will be tasked with designing “seed bomb catapults” where they will try to design a device that can fire their seed bombs into areas where plants can grow best.
  2. Let the students be creative and come up with their own designs.  

Part 3. Catapult and Catapult Seed Dispersal Discussion 

  1. Discuss how catapults are a specialized lever. The main features of catapults are fulcrums and lever arms.
    1. Fulcrums are the pivot point.
    2. Lever arms are used to make work or play or seed dispersal easier.
    3. Seesaws in the playground have a fulcrum and a lever arm.
    4. Plants take advantage of this concept for seed dispersal.
  2. Show pictures of plants that use catapult or explosion methods for seed dispersal. Discuss common features of these seed pods (long, thing, high pressure):
    1. Okra
    2. Rubber tree
  3. Explain how catapults and catapult seed dispersal works. 
    1. Pressure builds up in the seed pod and continues to build. This built up pressure is stored energy. That stored energy gets released when the seeds burst out. The stored energy or pressure provides the energy for seeds to travel distances. Seeds burst to move far away from the parent plant to avoid competition for resources of light, water and soil. The catapult is a similar concept. The catapult has stored energy when applied pressure. When the pressure is released the catapult launches the seed.

Part 4. Catapult Examples

  1. Consider showing an option or two for building catapults. 
  1. Directions for making a simple catapult can be included but let the kids explore and figure out their own designs.
  2. Demonstrate variables that are at play:
    1. How to change the location for a lever arm by moving the fulcrum.
    2. How to change the size of the lever arm
  3. Ask students to hypothesize which version of the catapult will allow for the seeds to travel farther. For example, a longer lever arm catapult will allow for the seeds to travel farther.

Popsicle Example

  1. Make a fulcrum by taking 8 of the popsicle sticks and tie a rubber band tightly around both ends.
  2. Make a lever arm by tieing another rubber band tightly at one bottom at the end of 2 sticks bound together.
  3. Next, carefully and slowly slide the fulcrum into the open end of the 2 sticks rubber banded together. 

Part 5. Students Build Catapults 

  1. Students will design at least 2 catapults.
  2. Hypothesize which design will allow for the seeds to travel the farthest.
  3. Test designs using pompoms or cotton balls. 
  4. Observe how far your cotton ball travels.
  5. Improve designs.

Part 6. Disperse Seeds 

  1. Choose a winning catapult design to disperse seed bombs into a garden.
  2. Catapult the seed bomb into a flower bed.  
  1. Watch and see how far the seed bomb flies and where it lands. 
  2. Repeat the steps again until all the seed bombs are gone.

Part 7. Seed Dispersal Discussion

Have students explain their experiment. Within this activity, students can harness all of their knowledge of ‘seed dispersal’ to explain how and why their catapult shoots the seed bombs in certain places. For example: “My seed bomb catapult shoots the seed bombs really high but not that far.  My catapult is really good for sending seed bombs to high cliffs and over tall trees.  My catapult shoots the seed bombs into areas where there are not a lot of other trees growing so that they can have plenty of room to grow and the shade from other trees wont stop our seeds from sprouting.”

Expected Experimental Results:

Students will build catapults that can disperse seeds.

Demonstration Materials:

Plants with longer and whisper structures would make better catapults. This is due to the concept provided in the image below, where longer lever arms can catapult material to further distances. 

  1. Catapult plant images.  

Catapult plant video.

Questions to Think About:

  1. Why is it important for plants to disperse their seeds?
  2. Why do plants use catapults or explosion methods to disperse seeds?
  3. What features are similar between the plants that catapult?
  4. List three different reasons seeds disperse from their plant.
  5. What does the plant need in order to grow and be healthy?
  6. Which model did you create that made a better catapult?
  7. How could your design be improved?
  8. Explain how and why the catapult shoots the seed bombs in certain places.

Chemistry:

Pressure builds up in the seed pod and continues to build. This built up pressure is stored energy. That stored energy gets released when the seeds burst out. The stored energy or pressure provides the energy for seeds to travel distances. Seeds burst to move far away from the parent plant to avoid competition for resources of light, water and soil. The catapult is a similar concept. The catapult has stored energy when applied pressure. When the pressure is released the catapult launches the seed.

Society:

There are many plants that release seeds by explosion. Okra and the rubber tree are two examples. The plants have common characteristics (long and thin pods). The seeds travel distances away from the parent plant so that they do not compete for resources.

Logistics:

STEM Subjects: 

Science (Biology, Physics and Chemistry) 

Science Vocabulary: 

Dispersal

Energy

Reproduce

Catapults (levers and fulcrums)

Stored energy

References:

Seed dispersal. (n.d.). Retrieved February 23, 2021, from  https://www.sciencelearn.org.nz/resources/103-seed-dispersal.

Funding:

CSU Internal Funding Sources:

  • IRA (Instructionally Related Activities Fund)
  • Faculty Small Grant

External Funding Sources:

  • Adobe