The Seed Story - Ecology Center

Using the Guide ■ Terrain For Schools Guide
About the Guide
The Ecology Center welcomes you
to Terrain for Schools, a unique
current events–based curriculum
for colleges and high schools. Lessons
in this guide address California State
Content Standards for grades 9-12
in three categories: science, social
studies, and language arts.
Overviews and applicable standards
are found on the first page of each
lesson. The lessons are designed to be
used with articles in the Winter 2002
issue of Terrain. Students will read
relevant article(s) before delving
into activities.
Teachers: Photocopy this material
as needed. Loan the guide to fellow
teachers. We welcome your feedback.
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TERRAIN FOR SCHOOLS is a
complimentary educational guide to
TERRAIN, Northern California's
Environmental Magazine, which is a
publication of the Ecology Center,
a non-profit environmental organization
serving the Bay Area since 1969.
Project Coordinator
Amy Kiser
Environmental Education Consultant
Blake Brown, Ron Sullivan
Curriculum Writers
Elaine Bond, Sheela Shankar, Jennifer
Stevenson, John Wilkinson
Graphic Designer
Edna Cabcabin Moran
Associate Publisher
Mary Vance
Webmaster
David Ricardo
Terrain Editors
Laird Townsend, Amy Standen
Ecology Center Executive Director
Martin Bourque
Ecology Center Board President
Leona Benton
Thanks to Vanessa Gregory and Amanda Lisle
for research and editing.
This issue of TERRAIN FOR SCHOOLS
is made possible through the
GENEROUS SUPPORT of the
Richard and Rhoda Goldman Foundation
and the Walter and Elise Haas Foundation.
Address all inquiries to:
TERRAIN FOR SCHOOLS
Ecology Center
2530 San Pablo Avenue
Berkeley, CA 94702
(510) 548-2220 x232
schools@ecologycenter.org
Terrain for Schools © Ecology Center 2002
Terrain Article: “O Pioneers!” page 35.
Introduction
Ponder This...
Science
The Seed Story
Overview
Students will:
• Learn the reasons for and diverse modes of seed dispersal.
• Collect seeds and make educated guesses regarding their dissemination methods.
• Build seed models from foil and test their ability to catch the wind.
• Calculate surface area-to-weight ratios.
• See page 23 for LANGUAGE ARTS extension activity.
Plants appear quite stationary. Unlike animals, they lack legs for running, arms
for climbing, wings for flying, or fins for swimming. Yet plants do get around. For
example, how did lush vegetation come to cover the barren lava islands of Hawaii in
the middle of the Pacific Ocean? How did weeds come to fill in the median strips of
some freeways? The answer is seed dispersal.
Most seeds have special adaptations that enable them to fly, float, roll, scatter, or
ride far away from their parent plants. If all seeds simply fell to the ground and stayed
beneath their parent plants, most would crowd each other, competing for light, space,
water, and nutrients. If disease, disaster, or a predator struck, more of the plant
population would be decimated if it was concentrated in one area.
Seed dissemination enables plants to maintain their population, expand their
range, or change the location of their range in response to
environmental change. For example, when a wildfire burns an
ecosystem, animals, wind, and flowing water help bring
seeds back to the scorched land, aiding recovery.
During the Second World War, bombs from German
airplanes set many fires in London. Soon after,
Londoners noticed a profusion of brilliant magenta
flowers in the burned-out patches. Some who had
never before seen these plants, called fireweeds,
wondered where they came from. These perennials,
which grow well in recently burned ground,
germinated from seeds the wind blew in
from the countryside.
• What are the pros and cons of seeds staying near to their parent plants?
• What are the pros and cons of seeds dispersing far from their parent plants?
• Compare this to your own choices as an offspring: What are the pros and cons
of relocating far from your parent(s)? What are the pros and cons of rooting
yourself close to your parent(s)?
CA BIOLOGY/LIFE SCIENCES STANDARDS, GRADES 9-12: Ecology 6. Stability in an
ecosystem is a balance between competing effects. c. Students know how fluctuations in population size
in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death.

The Challenge
Seeds have adapted many forms, that enable them to ride
the wind: a broad wing that spins like a helicopter propeller,
or hairs that form fluff or a parachute, like a dandelion.
Some seeds are minute, enabling them to sweep away in
wind currents. Can you design a seed that rides the wind?
Procedure
1. Each student receives a six inch square of aluminum foil
and a one inch square of paper.
2. Write your name on the small piece of paper; this
represents the seed embryo.
The Challenge
Wind-dispersed seeds have one thing in common: they
have a high surface area-to-weight ratio. This means the
seeds are light in comparison to their surface area, just like
kites. Figure out the surface area-to-weight ratios of these
four shapes.
Formulas to Know
Surface area to weight ratio =
Surface area of a sphere = 4πr2 Area of rectangle = length x width
Terrain For Schools Guide ■ Science
Windjamming Activity A
Using aluminum foil and paper, students will create
their own model seed for wind dispersal, then
measure the distance it travels in a fan’s current.
Materials
paper
scissors
electric fan
tape measure
aluminum foil
3. Design a seed out of foil, encasing the paper embryo
inside and pinching the aluminum into the desired
shape. Use ideas from the dispersal mechanisms on page
4 and/or from your own creativity. Seeds must fly from
the power of the fan only, not by throwing it like a
paper airplane.
4. Arrange a fan so that it blows horizontally along the
front of a sturdy chair.
5. One by one, students stand on the chair, drop their seed
from a specified height, and measure the distance it
traveled from the drop point.
6. After all seeds have dropped, open the embryo to
determine whose seed rode the wind the farthest.
When finished, recycle both foil and paper.
Flight Specs: Surface Area-to-Weight Ratio Activity B
Students will calculate the surface area-to-weight ratio
of a few different seed shapes to determine which
shape is best for wind dispersal.
surface area
weight
Follow-up Questions
• What did you think your seed would do? Why?
• Which seeds flew the farthest? Why?
• Which seeds flew less far? Why?
• What are some variables that could affect the distance
a seed reaches?
1
10
10
10
r = .5
w = 1
w = 1000
r = 5
1 w = 10
1
w = 100
1. This represents a heavy
seed, such as a coconut.
2. This column is similar
to the hairs on some
seeds such as dandelion
or thistle seeds.
3. This thin, aerodynamic
sheet is like the wing of
a maple seed.
4. This represents a tiny
seed such as the seed of
an orchid or the spore
of a fern.
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Science ■ Terrain For Schools Guide
Seed Dispersal Strategies
Wind Dispersal
Shaking: Wind blows a plant
with a dried ovary holding
seeds, flinging them out the
opening. Red campion is
one example.
Aerodynamic: Wind
currents blow seeds that
may be light, tiny, have a
wing, or are covered with
hair-like appendages that
make them airborne.
Maple, pine, ash, and elm
have winged seeds. Milkweed,
dandelion, cattail, and cottonwood
have hairy seeds. The seeds
of orchids and foxglove are
tiny, as are the spores of moss,
fungi, and ferns.
Animal Dispersal
Edible: Animals such as birds,
bats, mice, deer, and foxes eat
fruits containing seeds, which
pass through their disgestive
systems. The sweetness of
fruits is an adaptation that
lures animals to eat and thereby
disperse seeds. Blackberry,
toyon, and manzanita are
examples. Some seeds cannot
germinate until they pass
though an animal's digestive
system.
Some plants rely
on a single strategy
for seed dispersal.
Others produce seeds
adapted for multiple
dispersal strategies.
Some plant produce
seeds for both near
and far dispersal.
Cached: Animals and insects (like squirrels or ants)
sometimes hide seeds and nuts for future eating. These seeds
may sprout where they are cached (hidden). The nuthatch
collects acorns and hazelnuts, wedging them in the
branches of trees. Some fall when the bird goes to crack
them open, germinating below. One jay can collect several
thousand acorns in autumn preparing for winter and will
surely leave some behind.
Clinging: Barbs, burs, or sticky substances cling to animals
for transport. A bur is a cluster of dried fruits surrounded by
hooked spines. Queen Anne's lace, unicorn plant, and
cocklebur are examples. Mistletoe, which grows in trees, has
small berries birds like to eat. When birds eat the berries,
seeds stick to their bills. The birds wipe their bills off on
other tree branches, distributing the seeds.
Self-Dispersal
Gravity: Seeds fall directly under the
parent plant.
Explosive: Seeds develop within
a pod that squeezes or twists as
it dries up, eventually propelling
the seeds outward. The
seeds of witch hazel explode
up to a 40-foot distance!
Gorse seeds sound like gunshots
when they explode from
the pods. Water moves into the
stem of the squirting cucumber,
spitting seeds out of the fruit.
Hygroscopic: Some seeds use
moisture in the air to actually move
themselves across a surface. These seeds
have tiny hairs (or “awns”) which help them
move along the ground and screw into cracks. Wild oat
seeds move within a minute of a change in humidity.
A wild oat race has been held in England.
Water Dispersal
Drifting: Seeds that are
lighter than water float
atop the surface.
Usually they are large
and hollow or very
small and can float a
few feet or thousands of
miles. Coconut palm,
water lily, and lotus
seeds are examples. The
sea bean, a very hard
and buoyant tropical
seed that comes from
the world’s largest pod,
drops into and travels
down waterways to the
ocean, where it can
travel for thousands of
miles and remain viable
until it lands on
suitable ground.
Seabean
Raindrops: Rain droplets hit springboards or splash cups
that hold seeds, projecting them on impact. Bishop's-cap
has a springboard that can project seeds six feet away.
The chandelier plant also has a springboard. Lyre-leaved
sage has a splash cup design.

Procedure
1. Each student obtains three different seed types and brings
them to class.
2. Individually:
• Draw a picture of each of your seeds.
• Identify the plant type if you know it.
• Write where and how you collected it.
• Write how you think it may be dispersed, and why.
(Refer to page 4 for dispersal mechanisms.)
3. Group:
• Share all the seeds with the class.
• Discuss what the different shapes might say about how
they are dispersed.
• Divide the seeds into groups by size, morphology
(shape), or probable dispersal type.
Terrain For Schools Guide ■ Science
Collect and Study Seeds Activity C
Students will collect seeds from their neighborhood
or school grounds, draw them, share them, and
discuss likely dispersal mechanisms.
Glossary Terms
Big Ideas
How and Where to Find Seeds
• Look within fruits or vegetables.
• Search the trees or plants in your yard, school garden,
park, open field, abandoned lot.
• Walk through brush with your pants tucked in your socks,
or with socks over your hands.
• Wrap masking tape around your wrists and ankles with
the sticky side facing outward, then walk through weeds.
Although this activity can be
done year-round, fall is best
because many plants go to
seed during the driest season.
1. In order to maintain a green, weed-free grass lawn, humans must go to a lot of effort to
battle seed dispersal. What are some of the ways that they do this? Is continued human
interference necessary to prevent natural plant succession?
2. Wind dispersal is part luck. If a cottonwood tree lives for 100 years, it may produce
millions of seeds. Yet, for the cottonwood to reproduce, only one seed need sprout into a tree.
Nature does not waste organic material; dead seeds are eaten or they decay, enriching the soil.
Can you think of animals or insects that produce thousands of eggs or sperm, even though
only one is necessary to produce an offspring? What happens to the eggs and sperm that do
not develop into adult offspring?.
SEED: The mature ovule of a flowering plant. Seeds
usually contain an embryo, food reserves, and a seed
coat. The embryo often has a root, stem, and one small
leaf. Some embryos contain all the nutrients they need,
while other seeds hold nutrients in the endosperm, an
attached food packet. Endosperm is largely what we eat
when we eat corn, rice, or oats. The seed coat, or shell,
prevents drying, guards against infection, discourages
insects from eating it, and can pass safely through the
digestive systems of some animals.
FRUIT: The ripened ovary of a flower containing seed(s).
Note that in this lesson the term "seed" is used broadly
to describe various disseminules, sometimes including
fruits, which are commonly thought of as seeds.
SPORE: A single cell that grows into an entire plant. It
does not carry an embryo and lacks a seed coat.
Microscopic spores released by ferns, mosses, and fungi
are like dust and cannot be seen with the naked eye.
NUT: A large, hard, one-seeded fruit that does not
explode.
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