Sailing Seeds: An Experiment in Wind Dispersal
abstract objectives background materials procedure home references credits

Curricular Materials to Accompany the McIntosh Apple Development Poster
Distributed by the Education Committee of the Botanical Society of America
Posted March 2001

Grade Levels: 6-8; 9-12

Objectives:
At the end of this exercise, students will be able to:

• Identify different types of fruit and seed dispersal
• Design fruits/seeds so that they will disperse effectively in the wind
• Measure the distance the fruit/seed travels and estimate the time aloft
• Summarize their data in graphical format and analyze their results.
• Determine if there is a correlation between the distance a fruit or seed travels and the amount of time aloft

Background:
    Dispersal  of seeds is important for the continued survival of a plant species.  If plants grow too closely together, they compete for light, water, and soil nutrients; therefore, seed dispersal is a way to distribute offspring.  In flowering plants like apple trees, one or more seeds are housed within a fruit which is the portion of the apple that we eat.  Sweet fruit like apples are eaten by animals that disperse the undigested seeds.  In contrast, some plants have fruit that remain on the plant and disperse only the seeds.  In either case, plants have evolved different dispersal mechanisms.  Some fruits can be carried by water, like the coconut.  Burdock fruits have hooks that attach to and are dispersed by animals.  Dandelion fruits are suspended from feathery "parachutes" that are carried on the wind.  The fruit of maple and ash trees have wings that let them float on air.  This activity is a fun way for the students learn how fruit or seed size and shape influence their ability to disperse by wind.  Students design their own fruit or seed and measure two important qualities that enhance the ability of it to disperse in the wind: distance travelled and time aloft.

Materials:

• fruit and/or seed examples from sunflowers, dandelions, maple trees, coconuts, apples, peas, nuts, etc. (you may choose many different types or the same for each student).
• supplies to construct artificial "fruit" or "seeds" (paper, tape, sissors, glue, pipe cleaners, etc...)
• window or large fan
• meter stick or tape measure
• stop watch
• marker

Procedure:

• Set up lab stations with different types of fruits and seeds at each station (or a group of fruits/seeds with similar methods of dispersal).  Have  students record the fruit or seed type, type of dispersal, and sketch the fruit/seed. 
• After the students have viewed each fruit or seed, review what they have observed.  Ask questions that have students consider the relationship between the fruit or seed structure and its mode of dispersal.
• Distribute one sunflower fruit (commonly called "sunflower seeds") and supplies to construct a wind dispersal mechanism for the fruit.  Explain to the students that they will be placing their completed "fruit" in front of the fan and measuring the distance it disperses.  This is a competition to determine which travels the furthest.  In addition, they will be measuring the maximum time the "fruit" remains in the air--the maximum time aloft.
• After they have created their "fruit", the class will evaluate their dispersal characteristics.  Set the fan up on a desk blowing horizontally across the room.   Establish a standard drop site above the fan and set a tape measure along the floor beneath the fan.  Each "fruit" should be dropped by the student three times and the average used in their results.  Alternate students in charge of measuring the distance from the fan as well as measuring the time the "fruit" is in the air.
• For the second part of the experiment, have the students drop their "fruit" from a standard height (2 meters) while measuring time spent aloft with a stopwatch.  Repeat so that each student does three trials of this experiment.   Calculate the average of the three trials and record in the chart.
• After all the data has been collected, the students should graph the distance traveled and the time aloft.  Have students graph all of the classes data.
• The students should determine if a correlation exists between the maximum time aloft and the distance traveled from their graphs.

• Assessment Questions:

• Discuss with students why the winner's "fruit" traveled the furthest and lasted the longest in the air.
• What design did the winning "fruit" have?  Why was this a paricularly effective disperser?  That is, what may have contributed to the win?  Was it built better, stronger, lighter? How much paper or tape did the student use?  Do these affect the weight of the "fruit"?
• Does it matter how the student dropped the "fruit" in front of the fan?
• What other factors  in nature contribute to wind dispersal?
• Does it matter if the plant is higher from the ground?  In an open area?
• What are the advantages of wind dispersal? Are there any disadvantages?
• Is wind dispersal more likely in dry or fleshy fruits?