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Pg. 109-119 The Importance of Pollen and Seeds • Oak, maple, and other shade trees are seed plants. • All flowers are produced by seed plants. In fact, most of the plants on Earth are seed plants. • How do you think they became such a successful group? Reproduction that involves pollen and seeds is part of the answer. Pollen • In seed plants, some spores develop into small structures called pollen grains. • A pollen grain is a small structure produced by the male reproductive organs of a seed plant. Pollen • The sperm of seed plants are carried as part of the pollen grain by gravity, wind, water currents, or animals. • The transfer of pollen grains to the female part of the plant is called pollination. • After the pollen grain reaches the female part of a plant, sperm and a pollen tube are produced. • The sperm moves through the pollen tube, then fertilization can occur. Seeds • A seed consists of an embryo, stored food, and a protective seed coat. • The embryo has structures that eventually will produce the plant’s stem, leaves, and roots. Seeds • The stored food provides energy that is needed when the plant embryo begins to grow into a plant. • A new plant can develop more rapidly from a seed than from a spore. • The seed coat protects the seed from drying out. Gymnosperm Reproduction • Cones are the reproductive structures of gymnosperms. • Each gymnosperm species has a different cone. • The pine is a familiar gymnosperm. Cones • A mature female cone consists of a spiral of woody scales on a short stem. At the base of each scale are two ovules. • A female cone has 2 ovules where the eggs are produced. • Pollen grains are produced in the smaller male cones. Gymnosperm Seeds • Pollen is carried from male cones to female cones by the wind. • To be useful, the pollen has to be blown between the scales of a female cone. • If the pollen grain and the female cone are the same species, fertilization and the formation of a seed can take place. Angiosperm Reproduction • All angiosperms have flowers. • Most flowers have four main parts—petals, sepals, stamen, and pistil. Flower Parts and Functions Stamen – male reproductive part of a flower Anther – where the pollen is produced Filament – supports the anther Petal – attracts insects Sepal – protects the flower bud Pistil – female reproductive part of the flower Stigma – sticky top part that captures the pollen Style – pollen travels down this tube to the ovary Ovary – where eggs (ovules) are located Importance of Flowers • The appearance of a plant’s flowers can tell you something about the life of the plant. • Large flowers with brightly colored petals often attract insects and other animals. Importance of Flowers • As they move about the flower, the animals get pollen on their wings, legs, or other body parts. • Later, these animals spread the flower’s pollen to other plants that they visit. Importance of Flowers • Other flowers depend on wind, rain, or gravity to spread their pollen. • Their petals can be small or absent. Seed Dispersal • Plants have many ways of dispersing their seeds. • Most seeds grow only when they are placed on or in soil. • They fall onto the soil from the parent plant on which they grew. Seed Dispersal • In nature some seeds can be spread great distances from the parent plant. • Wind dispersal usually occurs because a seed has an attached structure that moves it with air currents. Seed Dispersal • Animals can disperse many seeds. • Some seeds are eaten with fruits, pass through an animal’s digestive system, and are dispersed as the animal moves from place to place. • Attaching to fur, feathers, and clothing is another way that seeds are dispersed by animals. Seed Dispersal • Water also disperses seeds. • Raindrops can knock seeds out of a dry fruit. • Some fruits and seeds float on flowing water or ocean currents. Germination • Germination occurs when the seed coat swells (because it received water) and breaks open and a plant grows from a seed. • Seeds will not germinate until environmental conditions are right. • Temperature, the presence or absence of light, availability of water, and amount of oxygen present can affect germination.