24.2 Seed Development and Germination

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24.2 Seed Development and Germination

• Essential Question
• How do fruits form?
• How are seeds dispersed?

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Seed and Fruit Development

• After fertilization, nutrients flow into the
  flower tissue and support the development of the
  growing embryo within the seed.
• As angiosperms seeds mature, the ovary walls
  thicken to form a fruit that encloses the
  developing seeds
• A fruit is a ripened ovary that contains
  angiosperm seeds.

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Figure 24-10
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Contd

• Parts of the ovule toughen to form the a seed
  coat, which is the outer layer of that protects
  the delicate embryo and its food supply
• The ovary wall thickens and may join with other
  parts of the flower stem
• The structures together form a fruit that
  encloses the seeds.

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Seed Parts 1. Embryo the zygote, which is
a tiny plant inside the covering. 2.
Cotyledons one or two seed leaves which store
food for growth. 3. Seed Coat keeps it from
drying out (some last thousands of years).
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The Structure of Seeds
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Seed Dispersal

• The endosperm nourishes the seedling NOT the
  fruit
• Seeds spread by animals are contained in fruit
  that entices them to eat it and thus spreads the
  seeds
• Animals include insects, birds, and mammals
• Seeds spread by the wind and water tend to be
  lightweight
• Seeds spread by animals is more efficient than
  seeds spread by the wind.

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Seed Dispersal Methods
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Seed Dormancy

• Dormancy - seed is alive but not growing
• Environmental factors such as temperature and
  moisture can cause a seed to end its dormancy and
  germinate
• Adaptive for plant by allowing for long-distance
  dispersal, temperature extremes

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Seed Germination

• Germination - early growth stage of plant embryo
• Early seeds absorb water causing food-storage to
  swell, cracking open the seed coat.
• The young root begins to grow and the seed leaves
  (cotyledon) emerges
• Monocot one seed leaf
• Dicot two seed leaves

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Monocot vs. dicot
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Figure 24-14
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Monocot Seed Germination

• Monocots grow straight up with coleoptile sheath
  covering shoot
• One embryonic leaf
• Seed remains underground

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Dicot Seed Germination

• Curved stem comes up out of soil
• Two embryonic leaves
• Seed goes above soil

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Parts of the Embryo

• Epicotyl - Grows into the leaves of the plant
• Hypocotyl - Becomes the stem
• Radicle - Becomes the root