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Reproduction in Flowering Plants. Sexual Reproduction in Plants. Flowers contain the sex organs of plants. They have four groups of organs: carpels, stamens, petals, and sepals. Sexual Reproduction in Plants. - PowerPoint PPT Presentation
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39 Sexual Reproduction in Plants
Flowers contain the sex organs of plants. They have four groups of organs: carpels, stamens, petals, and sepals.
39 Sexual Reproduction in Plants
• Carpels are female sex organs. A pistil is a structure composed of one or more carpels.
• The base of the pistil is the ovary, which contains one or more ovules.
• Each ovule contains a megasporangium.
• The stalk of the pistil is the style, and the end of the style is the stigma.
39 Sexual Reproduction in Plants
• Stamens are male sex organs.
• Each stamen is composed of a filament bearing a two-lobed anther, which consists of four microsporangia fused together.
• Petals and sepals of many flowers are arranged in whorls (circles) around the carpels and stamens.
• All parts of the flower are borne on a stem tip, the receptacle.
39 Sexual Reproduction in Plants
• The multicellular, diploid plant is called the sporophyte.
• In angiosperms (flowering plants), the diploid sporophyte generation is the larger and more conspicuous one.
• Cells contained in sporangia undergo meiosis to produce haploid spores.
• Mitosis produces the haploid plant (gametophyte)
39 Sexual Reproduction in Plants
• Female gametophytes, the megagametophytes, are called embryo sacs and develop in megasporangia.
• Male gametophytes, the microgametophytes, are called pollen grains and develop in microsporangia.
Mature embryo sac of lily
Pollen grains of an eudicot
39 Sexual Reproduction in Plants
• In angiosperms, the transfer of pollen from the anther to the stigma is called pollination.
• In some plants self-fertilization occurs by direct contact of anther and stigma before the flower bud opens.
Pollen grains adhere to sticky stigma.
39 Sexual Reproduction in Plants
• The pollen of many species is carried from plant to plant by wind. These plants produce pollen grains in great numbers.
• Water carries pollen to some aquatic plants.
• Animals such as insects, birds, and bats carry pollen among the flowers of many plants.
39 Sexual Reproduction in Plants
• Plants can cross-pollinate or self-pollinate.
• Many plants are self-incompatible; their stigma rejects the pollen from their own flowers.
• The stigma can also reject pollen from other species. Pollen from the same species binds strongly to the stigma; foreign pollen falls off.
39 Sexual Reproduction in Plants
• After a pollen grain lands on the stigma of a compatible pistil, a pollen tube develops from the grain.
• The pollen tube traverses the style until it reaches an ovule.
Pollen tube germinated in vitro.
39 Sexual Reproduction in Plants
• During transport through the pollen tube, the pollen grain cell undergoes one mitotic division to produce two haploid sperm cells.
• One sperm cell unites with the two polar nuclei, forming the 3n endosperm.
• The other sperm cell fuses with the egg cell, forming the diploid zygote.
39 Sexual Reproduction in Plants
• After fertilization, the zygote divides and the two daughter cells have different fates.
• One daughter cell produces the embryo and the other produces a supporting structure.
• The embryo is called a Cotyledon – an embryonic organ that stores and digests reserve materials (a “seed leaf”).
39 Sexual Reproduction in Plants
• In some species the cotyledons absorb the nutrient reserves from the endosperm.
• The seed will lose as much as 95 percent of its water content.
• The embryo remains quiescent in this desiccated state until conditions are right for germination.
39 Sexual Reproduction in Plants
• In flowering plants, the ovary wall together with its seeds develops into a fruit.
• Fruits serve to help seed dispersal.
• Winged fruit can be blown by the wind.
• Coconuts have spread from island to island by floating in the ocean.
• Some seeds hitch rides on animals.
• Fleshy, edible fruits may be eaten by birds and other animals and the seeds pass through the digestive tract.