Transcript Seed Dispersal and Germination

Mr. Chapman
Biology 20
Seeds can get around in a lot of
different ways thanks to several
evolutionary adaptations.
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Remember that conebearing plants do not
produce fruits as
reproductive structures.
Cone-bearing plants rely on
the wind, as well as gravity,
in order to spread their
seeds.
Cone-bearing Plants
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Flowering plants have fruit
to help disperse their seeds.
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Don’t forget that fruit is the
mature ovary of the flower.
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The ovary is the bottom
part of the pistil, the female
reproductive structure of
flowering plants.
Flowering Plants
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Seed dispersal is basically the process of spreading
seeds to a great area.
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It is important for a plant to be able to do this. If a
plant drops its seeds nearby, the resulting plants that
grow from it will have to compete for food and sunlight
with the parent plant.
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The new plant will also have to compete for space and
water, as well as all the nutrients in the soil
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Fleshy fruits, like apples and berries, attract animals
with their fragrant, nutritious offerings.
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When the animal eats the fruit, it digests everything
except for the seed. The seed has a tough outer
coating that protects it from the animal’s digestive
juices.
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Once the animals graces nature with his fragrant
excrement, the seeds are released along with an ample
supply of fertilizer.
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Often, this results in the release of the seed far from
the place that it was originally ingested, allowing the
plants to be spaced well apart from each other.
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Some plants have fruits that can stick to animals
instead, such as burrs. Eventually, the burrs
fall off of the animal, hopefully some
distance away from where they caught on.
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A lot of the time, seeds that are dispersed by the
wind have fruits attached to them that act like
parachutes or wings. This allows them to travel great
distances in the wind before they hit the ground.
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Some plants that grow near water produce fruits that
float. The coconut, for example, is a fruit that is
designed to be able to float on the water, and travel
to islands that are thousands of miles away.
• Once a parent plant releases its seeds, it could be
weeks, months, or even years until the seeds begin to
grow into new plants.
• Scientists recently found a 2000-year-old seed that
came from an extinct species of tree. When they gave
it the proper conditions to grow, it became a new
plant.
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A seed is in a state of dormancy when the embryo has
stopped growing.
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Different seeds require different conditions to come
out of dormancy. For many, all that is required is for
the seed to be exposed to proper temperature,
moisture, oxygen and light levels.
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For other seeds, such as the strawberry plant, the
outer seed coat must be mostly digested by an animal
before it exits dormancy. Can you think of why this is?
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Germination occurs when there are certain changes in
temperature, moisture, or light levels. During germination,
the embryo breaks out of the seed coat and begins to grow
into a seedling.
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This only occurs when the conditions for growth are proper
for the young plant to grow. Because of this, seeds can
survive many harsh conditions that young plants could not.
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The process begins when water begins to swell the sed,
causing it to crack the seed coat.
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Water comes in through the cracks and activates
enzymes that allow the embryo to break down its
endosperm into sugar, giving it a source of energy.
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The plant continues to grow upwards, with details that
you don’t need to know. Once the leaves emerge and
begin to make food through photosynthesis, the young
plant is called a seedling instead of an embryo.
http://www.youtube.com/watch?v=zbQ1jWl3AOM