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A Model of Seed Dispersal

Lesson Objectives
Related National Standards
Tools and Materials Needed
Teaching Strategy
Video Segments
Procedure
Assessment Recommendations
Extensions and Adaptations

Lesson Objectives

Plants have evolved many different strategies for dispersing their seeds: think of "helicopters" on a maple tree, the fuzzy head of a dandelion, or the tiny, sticky pods that sometimes attach to your pants, socks, and shoes as you walk through open fields.

In this lesson, students will learn about one particular method of seed dispersal, through foods that animals eat. Animals that eat fruits can't digest the seeds of the fruit, which pass unharmed through the digestive tract and are deposited on the ground some distance from the original plant. In this activity, students simulate that process and mark the dispersal location on state and local maps.

By the end of this activity, students will:

  1. Understand why plants have developed so that many seeds are not digested.
  2. Understand the need for each plant to produce numerous seeds.
  3. Understand that there are differences in the metabolism of various animals.
Subjects: Botany, biological interactions, life science, geography

Grade Level: Elementary and above.

Related National Standards from the McRel Standards Database at

http://www.mcrel.org/standards-benchmarks/

Science

  1. Understands how species depend on one another and on the environment for survival
  2. Knows ways in which species interact and depend on one another in an ecosystem (e.g., producer/consumer, predator/prey, parasite/host, relationships that are mutually beneficial or competitive)

Tools and Materials Needed

  1. A copy of the program "Wild Indonesia: Creatures of the Island Kingdom" (part 3)
  2. 2 pound bag of small candies or jellybeans
  3. Index cards
  4. Map of the town (USGS topographic maps would work or many states have county highway maps)

Estimated Time to Complete Lesson

Two days. One class period to watch the video, determine times for the students and distribute candies. One class period to plot dispersal on the map and discuss the results.

Teaching Strategy

Background Information

Plants have developed numerous ways to disperse their seeds to other areas. One of the common methods is by using animals that eat the seeds and then pass them through their systems unharmed when they defecate. This is often a superior way to the whims of wind, water or other environmental methods.

Plants that use this method tend to have a number of seeds within the fleshy fruit they produce. When the animal eats the fruit, the seed enters their system and remains inside as they travel. Depending upon the metabolism of the creature, and their common method of locomotion, the seeds may travel hundreds of miles before they are deposited. The defecated material may also act as a natural fertilizer in some cases.

Video Segments

Wild Indonesia: Creatures of the Island Kingdom

6:00 Video shows desolate area after volcanic eruption. Various plants are starting to grow in the area. Starting at 7 minutes, it discusses how wind and water distribute seed. From 7:45 to about 10:00, birds and bats as dispersal agents are discussed. Students may discuss the dispersal potential of other animals seen throughout the film.

Procedure

  1. Watch the Wild Indonesia: Creatures of the Island Kingdom video. Stop and discuss the section on seed dispersal and keep a running track of other animals seen throughout the video.

  2. Have a student helper take around the bag of candies and have each student take some. Do not tell them how many to take. The number of candies represents the number of seeds eaten by an animal.

  3. Determine the number of hours between your current time and the number of hours until 9 p.m. that night. Using the number of hours until 9 p.m. as the upper limit, have the students pick a number between 0 and that number. For example, if it is 10 am, there would be 11 hours until it would be 9 p.m., and 11 would be the upper limit. After the student picks a number, they should calculate their stop time. For example, if it's 10 a.m. and a student picks the number 9, his stop time would be 9 hours later, or 7 p.m. Have each student record his name and stop time, and number of seeds/candies on the card.

  4. Students should carry the card and candies the rest of the day. When they reach their stop time, they should record their location on the index card; at that time, they may eat the candies.

  5. The following day, students are to mark on the classroom maps their position when their time was up. Each map mark represents a new colony of the plant. Students that failed to take note of their position could represent animals that were eaten during that period and didn't deliver their seed.

  6. Discuss the amount of dispersal that occurred and what type of animal in the movie could have carried the seed that distance. Introduce the idea that different animals may digest their food at different rates.

Assessment Recommendations

Students may be assessed though their participation in the class discussion and participation in the activity. Students should write a paragraph explaining how plants using the environment and how other organisms may disperse seeds that would be scored using a teacher-made matrix.

Extensions/Adaptations

  1. The activity may be repeated on several different days of the week to look for a change in patterns. If conducted on Friday, the plant dispersal will be much wider than on a weekday. Students may calculate the area distance a seed travels or the average distance by the number of hours traveled.

  2. If small pebbles are substituted for the candies, the students can be told to carry the stones with them. At the appointed time, the students should both note their position and count the number of stones they have with them. This information can be used to calculate a percentage of the number of seeds that survived versus the ones that did not germinate.

 



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