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24.2 Seed Development and Germination

24.2 Seed Development and Germination. Essential Question How do fruits form? How are seeds dispersed?. Seed and Fruit Development. After fertilization, nutrients flow into the flower tissue and support the development of the growing embryo within the seed.

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24.2 Seed Development and Germination

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  1. 24.2 Seed Development and Germination Essential Question How do fruits form? How are seeds dispersed?

  2. 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.

  3. Figure 24-10

  4. Cont’d • 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.

  5. 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).

  6. The Structure of Seeds

  7. 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.

  8. Seed Dispersal Methods

  9. 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

  10. 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

  11. Monocot vs. dicot

  12. Figure 24-14

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

  14. Dicot Seed Germination • Curved stem comes up out of soil • Two embryonic leaves • Seed goes above soil

  15. Parts of the Embryo • Epicotyl - Grows into the leaves of the plant • Hypocotyl - Becomes the stem • Radicle - Becomes the root

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