Download What is a seed - Nanoscience Instruments

The Magnificent Seed
as Seen
through the Phenom
Scanning Electron Microscope
Portulaca Magic Carpet seed 355x
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Dorothy K. Moore, PhD
Chemeketa Community College
Salem, Oregon
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Portulaca Magic Carpet seed 355x
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Introductory Note to the Instructor
They often seem dry, lifeless, and inconsequential, but seeds are very much alive and
essential to all living things. As teachers, we have the opportunity to share with our
students insights about seeds and other areas of the natural world, a place that has become
foreign to children who spend increasingly more time indoors.
This document is meant to be an introductory source for the educator. It explains briefly
the structure of the seed and how that structure contributes to its ability to sprout. It also
discusses the various means of seed dispersal and lists a number of seeds that we eat
directly as food. At the end I’ve included a few resources I have found helpful while
researching this topic.
Most of the microscopic images in this document were captured using the Phenom table
top scanning electron microscope, an easy-to-use tool designed especially for teachers. If
you’re interested in more information on the Phenom or think you might like to obtain
one, you can visit the Phenom-World website at www.phenom-world.com. Otherwise,
you may simply use this document and its images as a springboard to your own study and
investigation of nature.
The seed is a highly significant instrument of creation. I trust you and your students will
find great satisfaction in researching and pondering its magnificence.
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celery seed 390x
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Seed defined
Just what is a seed? There are basically two ways to think about a seed: We can think of a
seed as the part of the plant that contains the embryo of that plant - the embryo being the
undeveloped form of the adult plant - or we can think of a seed as the small embryonic
plant itself. However we conceptualize it, the seed is an amazing little structure whose
form and function enable it to propagate and spread across the earth.
Seeds that are at rest and have not yet sprouted are considered dormant. In order for a
seed to come out of dormancy to sprout or germinate, certain environmental factors must
be in place: There must be the right combination of light (or darkness), oxygen
(generated by rain water in the soil), and water. When in the right combination, these
environmental factors cue the respiratory and metabolic functions within the seed that it
is time to wake up the embryo to prepare it for growth. When the embryo inside a
dormant seed “awakens” and resumes growing, we call the process “germination.”
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Hinders to the viability of seeds
In order to grow, the embryo within the seed must also be alive, but the viability of a seed
can be hindered in several ways: The seed can be empty, without an embryo from which
to grow; the embryo can be functionally incomplete; healthy seeds can become damaged
or killed by predators and pathogens; fires and floods can destroy seeds; extreme
temperatures can damage the embryonic plant; or a seed can simply die of “old age”
before it has a chance to germinate and grow.
Germination
Germination is the sprouting or growing of a seed. In order to sprout, viable seeds of
angiosperms and gymnosperms must be fertilized through the union of male and female
sex cells. Once fertilized, various chemicals, hormones, and structures within the seed
work together to grow the seed into a seedling.
Visible seed coat of a carrot seed 390x
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The seed coat or testa is the very outer membrane of the seed. The seed coat is usually
hard so that it can protect the inside embryo. The protective nature of the seed coat is
especially important during long periods of dormancy when the seed is at rest and in
need of protection from the threat of cold, extreme weather conditions, or excessive
moisture.
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http://www.botanical-online.com/llavorangles.htm
1. radicle – emerges first and will develop into the main root of the plant 2. plumule – like an
early leaf 3. hypocotlyl – space that will develop into a stem 4. cotyledon – food storage and/or
achieves the function of primary leaves 5. seed coat (testa) – out layer for angiosperms; the seed
coat for gymnosperms 6. micropyle – hole through which water enters
When all of the environmental conditions are right and the seed is ready for germination,
water will enter the seed through the micropyle, a small hole in the seed coat. As water
enters through the micropyle, the metabolic pathways necessary for inner growth become
activated.
fennel seed 2820x
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Beneath the seed coat is the endosperm, the fleshy area of the seed that provides food for
the embryo. Sometimes the endosperm is included within the cotyledon, the structure
that will develop into the first leaves of the seedling. Seeds possessing only one
cotyledon such as those found in grasses and palms, are called monocots; those with two
cotyledons are called dicots. Broad-leaved plants and most fruit and nut species are
dicots.
www.biologie.uni-hamburg.de/b-online/
The epicotyl contains the initial shoots of the seedling. In addition to becoming the first
leaves of the new seedling, the epicotyl also contains three embryonic leaves which help
absorb nutrients inside the seed.
The radicle is the main embryonic root which points towards the micropyle and absorbs
water into the embryo. As the embryo grows, secondary roots will join themselves to the
main root so that more water from the soil can be absorbed into the seed. The first stem
tip of the embryo is called the plumule. As water fills the embryo, the embryo swells up
until it eventually bursts out of its own coat.
http://theseedsite.co.uk/seedparts.html
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http://www.youtube.com/watch?v=d26AhcKeEbE&feature=related
Dormancy
Seeds germinate when they have the right amount of water, oxygen, and sunlight. But
even when all environmental conditions are perfect for growth, some seeds will remain
dormant for an extended period of time. This situation, known as “true dormancy”, is
caused by special conditions within the seed which prolong germination in order to
protect the species. For example, when a volcanic eruption destroys nearby wildlife –
including newly-germinated seeds – new seedlings will take the place of those that were
destroyed as soon as the environment becomes conducive for germination again. The
original seedlings may have perished in the volcano, but the species will lives on by that
process.
Other forms of dormancy include “physiological dormancy,” caused by conditions
within the embryo, and “physical dormancy,” caused by conditions outside the embryo
such as when the shell of a seed is too thick for water to pass through. “Induced
dormancy” occurs when the environmental conditions are not yet optimal for
germination and the seed must wait to germinate. “Combinational dormancy” occurs
when more than one of the above factors hinders germination.
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dandelion seed 365x [email protected]
dandelion seed 8800x
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Seed dispersal
Because plants do not physically move across the land as do animals, nature as
provided them with other ways for getting their seeds to areas of land favorable for
growth. Seed dispersal occurs in one of several ways:
www.clipart.com
Gravity: When fruit is ripe, it falls downward from the plant or tree. Examples
include apples, coconuts, and passion fruit.
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www.clipart.com
Wind: Seeds can float or flutter in the wind. Feathery pappus attach to milkweed,
poplar, and dandelion seeds to carry them long distances. Maple and pine seeds
have wings that allow them to flutter gently to the ground. Tumbleweeds blow
across the desert to disperse their seeds. Some seeds are so small that the wind
simply carries them away like dust.
Squirting cucumber
www.wikepedia.com
Self-dispersal (ballistic): The fruit tissue of some plants such as touch-me-nots or
squirting cucumbers, will suddenly contract and explosively discharge their seeds.
Water lily
www.clipart.com
Water: Water lilies are examples of plants that use hydrochory for seed
dispersal. The flowers produce a fruit that floats and drops to the bottom of the
pond where the seed takes root and grows into a new plant. Palm trees drop their
seeds (coconuts!) into the ocean. The coconut will float on strong ocean currents
until reaching dry land where it germinates and grows into a new tree.
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www.clipart.com
Dispersal by animals: Plant seeds can be dispersed by animals in a variety of
ways. A very few are transported externally by animals when spines, barbs, or
adhesive mucus on the seed attaches to fur and feathers. Animals might also
ingest and digest seeds through a process called edozoochory. Many animals
depend on plants to provide seeds as food, and many plants depend on animals for
the dispersal of their seed. Some seeds have appendages called elaiosomes that
ants like to eat. The ants will carry the seeds back to their nests, eat the nutritious
elaiosomes, but leave behind the inedible parts of the seed. The uneaten part of
the seed will eventually germinate and grow into a new plant. In this case the
plant depended on the ant to disperse its seed, and the ant depended on the tree to
provide to provide it with food, a symbiotic relationship called mutualism.
Some animals hoard and hide seeds in hidden caches. Squirrels and blue jays are
seed predators who hide precious seeds for later consumption. Seeds that are
buried and forgotten will germinate and grow into new plants.
Seed dispersal allows seeds to be dispersed far from the parent plant, ensuring the seed’s
survival. There are a number of reasons why seeds dispersed far from the parent plant are
more likely to survive: 1. Predators and pathogens tend to prey on seedlings concentrated
tightly together; therefore, seeds dispersed away from the crowd are often spared.
2. Seedlings that sprout further away from adult plants have far less competition for
sunlight and water. 3. Seeds that are dispersed far from the parent plant are also able to
reach habitats more favorable for their survival, and 4. new geographic regions and
habitats are colonized when seeds are dispersed far away.
www.clipart.com
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California poppy seed 3600x
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A word about spores
Is a spore a seed? Like a seed, a spore is a reproductive body capable of giving rise to a
new adult organism. Unlike seeds, however, spores do not contain significant food
storage, and must therefore rely totally on the environment for germination. Nonetheless,
the terms spore and seed are often used interchangeably.
thyme seed 420x
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popped corn 360x
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coffee bean 360x
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The edibility of seeds
Many seeds are edible. In fact, the majority of humans’ caloric intake comes from
seeds. Cooking oils, drinks, spices, and various food additives are just a few of the many
edible products that come from seeds. But seeds also can be directly consumed in the
form of cereals, beans, and nuts.
grassy seed 264x
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Cereals
Botanically speaking, cereals (grains) are crops with a grass-like structure that are
harvested for their dry fruit seed. People throughout the world consume half of their
calories from cereal, the seeds of which are often ground into flour. True cereals are
members of the Poaceae or Grass family, whereas pseudocereals are non-grasses that are
used the same way as cereals.
In their whole-grain form, cereals are rich in vitamins, minerals, carbohydrates,
fats, oils and protein.
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whole wheat flour 2360x
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white bread flour 1980x
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yellow grain of cornmeal 405x
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white grain of cornmeal 480x
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 Some examples of cereals include barley, maize (corn), pearl millet, oats, rice,
rye, sorghum, spelt, wheat, and wild rice.
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flax 570x
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 Some examples of pseudocereals include buckwheat, cattail, chia, flax, grain
amaranth, quinoa, and acacia seed.
chestnuts
www.wikepedia.org
Nuts
A nut is a hard-shelled seed, the fruit of certain plants. Although not all seeds are
nuts, all nuts are seeds. The fruit of a true nut is usually a semi-hard kernel surrounded by
an ovary wall that hardens as it matures. The seed of a nut is indehiscent, meaning the
fruit does not open to release the seed.
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hazelnut
www.ohnuts.com
 Examples of botanical nuts include acorn, beechnut, chestnut, hazelnut, oak
Some seeds that are not nuts botanically speaking, are still called nuts in the
culinary sense.
walnut
www.wikipedia.org
 Examples of culinary (not botanical) nuts include cashews, macadamia, walnuts.
cherry
www.clipart.com
Other seeds we refer to as nuts are actually drupes, stone fruits with a hard, inner
layer containing the embryo (kernel) and two hard or fleshy outer layers.
 Examples of drupes include pistachio, almond, pecan, avocado, cherry, peach,
coconut, mango and raspberry.
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stone pine cone and nuts
www.bing.com
 Examples of nut-like gymnosperms include the pine nut, juniper, cycad, and
single-leaf Pinion.
Some nuts are actually Legumes or beans, the category of seeds we look at below.
endosperm of garden bean 2800x
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Beans (Legumes)
Beans (Legumes) are soft seeds rich in protein. Because they are high in the
essential amino acid lycine but low in the essential amino acid methionine, legumes are
best paired with complimentary grains. Common pairings include beans with corn
tortillas, tofu with rice, and peanut butter on whole wheat bread.
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peanut shell 1420x
Kyle Erf, University of Arkansas
 Examples of beans (legumes) include chickpeas, fava, lentils, lupins, peanuts,
peas and soybeans.
peanut
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seed
www.saburchill.com
So there, “in a nutshell,” is an introductory overview of the magnificent seed as seen
through the Phenom scanning electron microscope. Much more is waiting to be
discovered about seeds online, in books, outside, or under the microscope. All we need to
do is look.
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Help Resources for More Information
General Information and/or Visuals
http://theseedsite.co.uk/seedparts.html
good image of test, coat, shoot, root
http://www.ehow.com/about_5409451_three-main-parts-seed.html
three main parts of the seed. (no visuals)
http://www.botanical-online.com/llavorangles.htm
diagram leaves room for labeling below or to the side.
http://www.botanical-online.com/english/medicinalblueberry.htm
medicinal properties of Blueberries. This is a good site beyond use with the module!
http://wiki.answers.com/Q/What_are_the_parts_of_the_seed
simple answers to questions
http://www.saburchill.com/chapters/chap0047.html
diagram related to germination.
http://aggie-horticulture.tamu.edu/Wildseed/info/3.1.html
overview of germination
http://www.ehow.com/how-does_4644403_a-seed-germinate.html
germination
http://www.buzzle.com/articles/seed-germination-process.html
germination
http://gardening.wsu.edu/library/vege004/vege004.htm
gardening information from western Washington.
http://www.ag.ohio-state.edu/~seedbio/seed_id/apiaceae/anethum_graveolens.html
images of all kinds of seeds
http://plantphys.info/seedg/seed.html
info on germination. Fact sheet
http://jxb.oxfordjournals.org/cgi/content/full/53/370/947
scholarly article on cereal seed storage protein
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Lesson Plans
http://quorumsensing.ifas.ufl.edu/HCS200/Seed.html
has simple lesson ideas related to seed vigor.
http://www.units.muohio.edu/labs/Heckman_Inquiry_Lesson.pdf
high school germination lesson plan.
http://www.accessexcellence.org/AE/SH/NSTA_NOR/morris_seeds.php
high school experiments with radish seeds
http://mypages.iit.edu/~smile/bi9417.html
lesson plans for seeds.
http://www.lessonplansinc.com/science.php/biology/lessonplans/C123/
links to lesson plans for seeds
http://kids.britannica.com/comptons/article-200875/flower
explains fertilization
http://www.biologie.uni-hamburg.de/b-online/ibc99/koning/seedgerm.html
for high school or college: seed germination diagram.
http://www.schools.utah.gov/curr/science/core/plans/int/seed.html
seed germination lesson plan.
http://www.woodrow.org/teachers/esi/1998/p/effects/seedgermination.htm
lesson plan for grades 7 – 12
Videos and Animation
http://www.youtube.com/watch?v=d26AhcKeEbE&feature=related
YouTube of radish germination. 2 minutes. No words.
http://www.youtube.com/watch?v=rDN0yAFcQok&NR=1
YouTube germination. Seed and root area only. 25 seconds
http://www.youtube.com/watch?v=iFCdAgeMGOA&feature=related
time lapse germination - roots and leaves 36 seconds.
http://www.youtube.com/watch?v=eelwEB4Z1GA
germination of seeds “planted” in paper.
http://www.botanical-online.com/animation4.htm
this one shows an animation of germination
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http://www.youtube.com/watch?v=To2DlJwErao&feature=related
germinating seeds in paper towels
Books
Back, C. & Watt, B. (1984). Bean and plant. Englewood Cliffs, NJ: Silver Burdett Press.
Lyle, S. (2006). Fruits and nuts: A comprehensive guide to the cultivation, uses and
health benefits of over 300 food-producing plants. Portland, OR: Timber Press
Toogood, A. (2002). American Horticultural Society: Growing from seed. London: DK
Publishing
Biologie.uni.hamburg.de
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