Biology Semester II |
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| Sections: |
Introduction | Section 1 | Section 2 | Section 3 |
| Section Two: |
Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9 |
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Biology: Flowering Plant Reproduction: Part Two Angiosperms: The Flowering Plants In angiosperms, the seed is covered or protected (angio = vessel or container; sperm = seed). Each plant in this division produces modified leaves grouped into flowers. These flowers in turn develop fruits and seeds. Most angiosperms have larger xylem cells, known as vessels, that improve the efficiency of their vascular systems. When angiosperms reproduce sexually, they produce a diploid zygote and a triploid endosperm. The zygote is a single diploid cell that divides to become the embryo, the next generation sporophyte. The endosperm is a tissue that nourishes the developing embryo. There are 235,000 known living species of flowering plants. In the classical view of flowering plant evolution, the early angiosperms were evergreen trees that produced large Magnolia-like flowers. A competing view contends that first angiosperms were actually tropical herbaceous plants with mixed monocot and dicot features. In either case, the flower is a unique collection of features that merits further study. Flowers A flower is a collection of reproductive and sterile tissues arranged in a tightly whorled array. Sterile (non-reproductive) parts of flowers are the sepals and petals. The stamen is the male reproductive part of the flower. Stamens are collectively called the androecium. The carpel (or pistil) is the female reproductive structure. Collectively, the carpels make up the gynoecium. Botanists interpret all flower parts as modified leaves. There are many different types of flowers. Perfect flowers are those with fully functioning male and female reproductive parts. In an imperfect flower, only the male parts or the female parts are functional. In an imperfect female flower, the male parts either do not develop, or develop but remain sterile. Complete flowers have all floral parts present. An incomplete flower is lacking one or more parts, such as petals. For example, the female flower of the corn plant (the corn cob) has no petals or stamens. The male flower of the corn plant (the corn tassel) lacks petals and carpels. Flowers can be solitary on a stem, like a tulip or a daffodil. Many times, though, numerous flowers are arranged on a single stalk. This is called an inflorescence.
Plants that have both sexes functional on the same plant are called monoecious (from mono meaning “one” and ecious meaning “house”). Corn plants fall into this category since both the male and female flowers are found on the same plant. The lily is a monoecious plant whose flowers are perfect and complete. For olive trees and mulberry trees, the male flowers are produced by a male plant and the female flowers made on a female plant. This situation is known as dioecious, or “two houses.” In Maricopa County, Arizona, it is illegal to plant male mulberry or male olive trees. The immense amounts of pollen they produce cause many residents to have allergic reactions.
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