Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

24-2 Seed Development and Germination Photo Credit: ©Carl R. Sams II/Peter Arnold, Inc. Copyright Pearson Prentice Hall

Seed and Fruit Development How do fruits form? Copyright Pearson Prentice Hall

Seed and Fruit Development As angiosperm seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. Copyright Pearson Prentice Hall

Seed and Fruit Development A fruit is a ripened ovary that contains angiosperm seeds. As seeds mature, the ovary walls thicken to form a fruit that encloses the developing seeds. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dispersal How are seeds dispersed? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dispersal Seed Dispersal Seeds are dispersed by animals, wind, and water. Seeds dispersed by animals are typically contained in fleshy, nutritious fruits. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dispersal Seeds of many plants are eaten by animals. These seeds are covered with tough coatings that protect them from digestive chemicals, allowing them to pass through an animal’s digestive system unharmed. The seeds then sprout in the feces eliminated from the animal. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dispersal Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dispersal Some seeds are encased in winglike structures that spin and twirl, helping them glide from their parent plants. A coconut is buoyant enough to float in seawater within its protective coating for many weeks. Tumbleweed plants break off at their roots and scatter their seeds as they are blown by the wind. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dormancy Seed Dormancy Many seeds will not grow when they first mature. These seeds enter a period of dormancy, during which the embryo is alive but not growing. The length of dormancy varies in different plant species. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dormancy What factors influence the dormancy and germination of seeds? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Dormancy Environmental factors such as temperature and moisture can cause a seed to end dormancy and germinate. Seed dormancy can be adaptive in several ways: allows for long-distance dispersal allows seeds to germinate under ideal growth conditions Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Germination Seed Germination Seed germination is the early growth stage of the plant embryo. When seeds germinate, they absorb water which causes food-storing tissues to swell and crack open the seed coat. The young root grows through the cracked seed coat. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Germination In most monocots, the single cotyledon remains underground. The growing shoot emerges while protected by a sheath. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Germination Foliage leaves Young shoot The corn seedling is a monocot in which the shoot grows directly upward, protected by its sheath. Germinating seed Primary root Corn (monocot) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Germination In dicots, germination takes place in one of two ways. In some species, the cotyledons emerge above ground, protecting the stem and first foliage leaves. In other species, the cotyledons stay underground and provide a food source for the growing seedling. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Seed Germination Foliage leaves Young shoot Cotyledons Cotyledons Seed coat The garden bean is a dicot in which the cotyledons emerge aboveground. Primary root Germinating seed Bean (dicot) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 A germinating corn seedling has a single cotyledon, which remains below ground. two cotyledons, which push above ground. a single cotyledon, which pushes above ground. two cotyledons, which remain below ground.     Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 Angiosperm fruits develop from the ovary wall of the flower. seed endosperm. swollen sepals of the flower. flower stamens. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 An example of a seed that is transported by water is a coconut. tumbleweed. blackberry. maple seed. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 The seeds of many plants that form fruits are dispersed mainly by animals. water. wind. the plant itself. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 24-2 An environmental condition that can cause the activation of a dormant seed is a sharp drop in temperature. the heat from a forest fire. an extended drought. falling from a great height. Copyright Pearson Prentice Hall

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