Transcript 24.2_Fruits_and_Seeds

1 Explain Why is it adaptive for some seeds to remain
dormant before they germinate
Apply Concepts The seeds of a bishop pine
germinate only after exposure to the extreme heat
of a forest fire. Evaluate the significance of this
structural adaptation
2 Pose a Question A new angiosperm species is
discovered. What questions would you ask before
predicting how its seeds are dispersed- explain why
you would ask each.
CH 24 PLANT REPRODUCTION AND RESPONSE
24.2 Fruits and Seeds
Seed and Fruit Development
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After fertilization, nutrients flow into the flower
tissue and support the development of the
growing embryo within the seed
Fruit
Mature angiosperm ovary, usually containing seeds
Fruit isn’t limited to “fruits” like apples but also
includes rice, corn, etc…
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Ovary wall surrounding a fruit may be fleshy,
(grapes and tomatoes) or tough and dry (shell that
surrounds peanuts).
Dispersal by Animals
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Many seeds especially those in sweet, fleshy fruits
are often eaten by animals
Seeds are covered with tough coatings, allowing
them to pass through an animal’s digestive system
unharmed
Seeds then sprout in the feces of the animal.
Dispersal by Animals
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Fruits provide nutrition for the animal
Help the plant disperse its seeds
 Often
to areas where there is less competition with
the parent plants.
Dispersal by Animals
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Dry fruits sometimes have burrs or hooks that
catch in an animal’s fur.
Dispersal by Wind and Water
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Typically contained in lightweight fruits that allow
them to be carried in the air or in buoyant fruits
that allow them to float on the surface of the
water
 Dandelion
 Coconut.
seed
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Dormancy
 Embryo
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is alive but not growing
Germination
 Growth
of plant embryo resumes.
How Seeds Germinate
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Seeds absorb water
 Causes
food-storing tissues to swell and crack open the
seed coat
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Young root emerges and begins to grow
Shoot then emerges.
The Role of Cotyledons
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First leaves
Store nutrients and transfers them to growing
embryo as the seed germinates.
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Monocots have one cotyledon
Stays underground to nourish young plant
Growing monocot shoot emerges from the soil
protected by a sheath.
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Dicot have two cotyledons
Lack protection of a sheath for plant tip
Upper end of the shoot bends to form a hook that
forces its way through the soil
Protects tip of plant, which straightens as it
emerges into the sunlight.
Advantages of Dormancy
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Allow for long-distance dispersal
Allow for seeds to germinate under ideal growth
conditions
Some seeds need cold temperature before seeds
germinate.
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1.
2.
The graph shows germination rates for Arisaema
dracontium gathered at two locations.
Interpret Graphs What effect does chilling have on
germination of seeds from Ontario. How does it
effect seeds from Louisiana
Form a Hypothesis Describe how the different rates
of seed germination might be explained in terms of
adaptation to the local climate