Key concepts
Biology
Plants
Evolution
Aerodynamics
Introduction
Have you ever looked outside on a windy day and seen "helicopter" seeds spinning through the air? Or picked up a dandelion and blown on it, sending the tiny, fluffy seeds flying all over the place? Wind is very important for dispersing seeds to help plants reproduce. In this project you will design some of your own "seeds" and see which ones work best when they are blown across the room by a fan.
Background
Dispersal of seeds is very important for the survival of plant species. If plants grow too closely together, they have to compete for light, water and nutrients from the soil. Seed dispersal allows plants to spread out from a wide area and avoid competing with one another for the same resources.
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Seeds are dispersed in several different ways. In some plants seeds are housed within a fruit (such as apples or oranges). These fruits, including the seeds, are eaten by animals who then disperse the seeds when they defecate. Some fruits can be carried by water, such as a floating coconut. Some seeds have little hooks that can stick on to an animal's furry coat. (You may have gotten them stuck on your clothing if you ever went hiking in the woods or tall grass.)
Other seeds are dispersed by the wind—such as the "winged" seeds from a maple tree that spin and "helicopter" through the air as they fall or the light feathery seeds from a dandelion that can catch on the breeze. The longer a seed stays in the air, the farther it can be blown by the wind, helping the plant species widely scatter its offspring. In this project you will make your own artificial "seeds" from craft materials. Can you design seeds that will stay in the air for a long time?
Materials
Examples of different seeds that are dispersed by the wind (Depending on where you live, you may be able to find some of these seeds outside. If you have access to the Internet, you can also do a Web search for maple seeds, dandelion seeds and other types of wind-dispersed seeds to help get ideas.)
Small, uniform, lightweight objects that you can use as "seeds" (For example, you could use small paper clips or small binder clips; or purchase a bag of real seeds—such as sunflower seeds—at the supermarket.)
Craft supplies to build dispersal mechanisms for your seeds (These could be as simple as paper and tape or you could also use things such as streamers, cotton balls or even items you find outside, such as blades of grass.)
Scissors, tape and glue for cutting and attaching your craft supplies to your seeds (Be careful when using scissors.)
A window fan or large box fan (Use with caution and appropriate supervision.)
Stopwatch or timer (optional)
Measuring tape or ruler (optional)
Preparation
Clear an open area in the room where you will do the seed-testing activity.
Place the fan on a table or chair, aimed across the room. You can also do the experiment outside on a windy day.
Procedure
Design and build several—at least four—dispersal mechanisms for your seeds. The activity works best if you can create at least two similar dispersal mechanisms to test against one another (see examples below). You can use your imagination and come up with your own ideas but here are a few to get you started (using a paper clip as an example "seed"):
Attach a paper clip to a small, square piece of paper, about the size of a Sticky Note, without making any changes to the paper.
Attach a paper clip to another small piece of paper, but make a several parallel cuts in one side of the paper to give it "frills," and bend them outward.
Attach a paper clip to a cotton ball.
Attach a paper clip to a cotton ball that you have pulled on to expand it a bit and make it wispier.
Cut out some paper in the shape of a maple seed and attach a paper clip.
Which seed dispersal mechanism or mechanisms do you think will travel the farthest when dropped in front of the fan? Why?
Turn on the fan. Standing in the same place, try dropping your seeds one at a time in front of the fan. Also try dropping a plain "seed" (for example, a regular paper clip with nothing attached) to see what happens.
How far do the seeds get blown by the fan? Do certain seeds take longer to reach the ground than others?
Think about your results. Did some of your designs not work at all (fall straight down, without blowing forward)? Did some work better than others?What can you do to improve your designs? Can you make changes to your seeds to make them blow even farther?
Extra: Have a friend use a stopwatch to time how long it takes the seeds to hit the ground. This might be easier if you drop the seeds from a higher location. (Have a tall adult drop them, carefully stand on a chair or drop them from the top of stairs.)
Extra: Use a tape measure to record how far the seeds travel horizontally from where you drop them to where they hit the ground. Which seeds go the farthest?
Extra:How do your results change if you change the speed of the fan?
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Observations and results
You should find that adding light materials to the "seed" can make it fall more slowly and blow farther—however, the shape of the materials is also very important. For example, a paper clip attached to a crumpled-up piece of paper will still fall very fast. A piece of paper with a "wing" design (similar to that of a maple seed) or a bunch of individual streamers (like a dandelion seed), however, will fall more slowly and be blown farther by the fan. Exactly how far the seeds blow will depend on the strength of your fan but you should definitely see a difference in the horizontal distance traveled between a "plain" seed and one with a dispersal mechanism. When you take your best designs and try to improve on them, you mimic the process of evolution—because the "best" seed designs in nature are the ones most likely to reproduce!
More to explore
Gone With the Wind: An Experiment on Seed and Fruit Dispersal, from Science Buddies
Sailing Seeds: An Experiment in Wind Dispersal, original project from the Botanical Society of America
Make a Whirlybird from Paper, from Scientific American
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies
