Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Mosses • The life cycle of mosses alternates between clumps of gametophytes (the dominant generation) and a sporophyte that consists of a spore capsule on a bare stalk. • Moss gametophytes produce gametes in two types of reproductive structures: antheridia (singular, antheridium), and archegonia (singular, archegonium).

Section 1 Plant Life Cycles Chapter 30 Alternation of Generations Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Mosses, continued • An antheridium is a male reproductive structure that produces hundreds of flagellated sperm by mitosis. • An archegonium is a female reproductive structure that produces a single egg by mitosis. • Sperm break out of the antheridia and swim to archegonia. One sperm fertilizes one egg to produce a diploid zygote. • The zygote undergoes repeated mitotic division and forms a sporophyte, which remains on the gametophyte.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Mosses, continued • Soon, the cells at the tip of the sporophyte will form a sporangium, called a capsule. • A capsule of a moss is the part of the sporophyte that will create haploid spores. • Mosses will only produce one type of spore. When only one type of spore is produced it is called homospory.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Mosses, continued • When the spores are mature, the capsule will split open, and the spores are carried away by the wind. • Spores that land in favorable environments may germinate and grow into new gametophytes.

Section 1 Plant Life Cycles Chapter 30 Life Cycle of a Moss

Section 1 Plant Life Cycles Chapter 30 Life Cycle of Mosses Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Ferns • The life cycle of ferns is similar to mosses, but it is also different. • Most ferns are homosporous and produce a sporophyte that grows from the gametophyte. • However, the sporophyte, not the gametophyte, is the dominant generation in ferns.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Ferns, continued • The fern’s gametophytes are tiny and are anchored to the soil by rhizoids. They can produce both antheridia and archegonia. • Water must be present in order for the egg to be fertilized. • Once the egg is fertilized, it will soon form a zygote and then a sporophyte.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Ferns, continued • Once the sporophyte can survive on its own, the gametophyte will die. • Once mature, a fern sporophyte will have leaves that are called fronds. • Fronds grow from an underground stem, or rhizome, and contain cells on their underside that develop into sporangia.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Ferns, continued • In many ferns, the sporangia on the underside of a frond are clustered together. • A cluster of sporangia is called a sorus. The sorus will produce haploid spores. • Once the spores have matured, they will be carried away by air currents. When the spores land, they may grow into new gametophytes.

Section 1 Plant Life Cycles Chapter 30 Life Cycle of a Fern

Section 1 Plant Life Cycles Chapter 30 Life Cycle of Ferns Click below to watch the Visual Concept. Visual Concept

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms • Gymnosperms will produce two types of spores—male microspores and female megaspores. • Microspores will grow into male gametophytes, and megaspores will grow into female gametophytes. • When different types of asexual spores are produced it is called heterospory.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • The microspores of heterosporous plants produce male gametophytes that stay attached to the sporophyte and develop into pollen. • Pollen allows sexual reproduction in seed plants to take place independent of seasonal rains or other periods of moisture.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • However, gymnosperm sexual reproduction can take more than two years. • During the first summer, a mature pine tree produces separate female and male cones, which produce male (microsporangia) and female (megasporangia) sporangia. • The following spring, the cells in all sporangia undergo meiosis and divide to produce haploid spores.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • Megasporangia are haploid spores that produce megaspores, which develop into megagametophytes, or female gametophytes. • A thick layer of cells called an integument surrounds and protects each megasporangium. • Each integument has a small opening where pollen can enter, called the micropyle. • Together, a megasporangium and its integument form a structure called an ovule.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • Microsporangia produce microspores, which develop into microgametophytes, or male gametophytes. • A pollen grain is a microgametophyte of a seed plant.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • The male cones of a pine release huge numbers of pollen grains into the wind. • When the pine pollen lands on a female cone, it will drift between the cone scales until they reach the ovules. • The transfer of pollen, the male gametophyte, to ovules, the female gametophyte, is called pollination.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • During pollination, the pollen grain is drawn into the ovule through the micropyle, and induces the ovule to produce archegonia and eggs. • After pollination, the pollen grain begins to grow a pollen tube. • The pollen tube is a slender extension of the pollen grain that enables sperm to reach an egg.

Section 1 Plant Life Cycles Chapter 30 The Life Cycle of Gymnosperms, continued • Pine sperm do not have flagella and they do not swim to an egg. The pollen tube carries the maturing sperm to the egg. • When the pollen tube reaches an archegonium, one sperm unites with an egg to form a zygote. • Over the next few months, the zygote develops into an embryo as the ovule matures into a seed.

Section 1 Plant Life Cycles Chapter 30 Life Cycle of a Conifer

Section 1 Plant Life Cycles Chapter 30 Life Cycle of Conifers Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Objectives • Identifythe four main flower parts, and state the function of each. • Describegametophyte formation in flowering plants. • Relateflower structure to methods of pollination. • Describefertilization in flowering plants.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower • Early land plants lacked leaves and roots and consisted of only stems. • Leaves evolved from branches of stems, and flowers are considered to be highly specialized branches and the parts of a flower to be specialized leaves. • The specialized leaves of a flower form on the swollen tip of a floral “branch”, which is called a receptacle.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower, continued • Flower parts are usually found in four concentric whorls, or rings. • The outer whorl is called the sepals, which protects the other parts of a developing flower before it opens. • Petals make up the next whorl, and can vary drastically between plants. Some plants have brightly colored petals, and other plants have petals that are small or absent.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower, continued • The male reproductive structures are stamens, each of which consists of an anther and a filament, and are found on the third whorl of the flower. • An anther contains microsporangia, which produce microspores that develop into pollen grains. • A stalklike filament supports an anther.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower, continued • The innermost whorl contains the female reproductive structures, which are called carpels. • One or more carpels fused together make up the structure called a pistil, which is the main female reproductive structure in flowering plants.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower, continued • The base of a pistil contains the ovary, which will produce eggs in ovules. • A style, which is usually stalklike, rises from the ovary. • The tip of the style is called the stigma, which usually is sticky or has hairs in order to trap pollen grains.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Floral Structure

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Flower Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of an Angiosperm Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation • In angiosperms, gametophytes develop within the reproductive structures of flowers. • Embryo sacs, which are the female gametophytes in angiosperms, form within the ovary of the pistil. • Pollen grains, the male gametophytes, form within the anthers of the stamens.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Embryo Sac Formation • In flowers, ovules form in the ovary of a pistil. • An angiosperm ovule consists of a megasporangium surrounded by two integuments, which do not completely enclose the megasporangium. • At one end of the ovule is the micropyle, through which a pollen tube can enter.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Embryo Sac Formation, continued • An ovule contains a large diploid cell called a megaspore mother cell. • A megaspore mother cell undergoes meiosis and produces four haploid megaspores. • The maturing megaspore undergoes three mitotic divisions, which produce a cell that has eight haploid nuclei.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Embryo Sac Formation, continued • The haploid, megaspore nuclei migrate to certain locations within the cell. • The nuclei are initially arranged in two groups of four at the top and bottom of the cell. • Two nuclei will come to the center from the ends or poles and are called polar nuclei. These are the nuclei that will eventually fuse with the sperm cells.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Embryo Sac Formation, continued • The other six nuclei within the megaspore mother cell help the polar nuclei be fertilized by the sperm and then eventually die after fertilization occurs. • The megaspore mother cell is now called the embryo sac and contains eight nuclei—seven smaller cells and a large central cell that encloses all the other cells.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Embryo Sac Formation, continued • The embryo sac is also known as the mature female gametophyte, or megagametophyte. • The surrounding integuments and the embryo sac now form a mature ovule, which when fertilized will develop into a seed.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Formation of A Female Gametophyte

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Ovule Formation in an Angiosperm Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Pollen Grain Formation • An anther contains four microsporangia, or pollen sacs. • Initially, the pollen sacs contain many diploid cells, and are called microspore mother cells. • Each of these microspore mother cells will undergo meiosis and produce four haploid microspores.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Pollen Grain Formation, continued • Each microspore undergoes mitosis and produces two haploid cells that do not separate. • Once the cells are haploid, a thick wall then develops around the microspore. • The resulting two-celled structure is a pollen grain, which is the male gametophyte, or microgametophyte.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Gametophyte Formation, continued Pollen Grain Formation, continued • The larger of the two cells is the tube cell, from which the pollen tube will form. • The generative cell, which is enclosed in the tube cell, will divide by mitosis to form two sperm.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Formation of A Male Gametophyte

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Pollen Grain Formation Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Parts of a Pollen Grain Click below to watch the Visual Concept. Visual Concept

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Pollination • In flowering plants, pollination occurs when pollen grains are transferred from an anther to a stigma. • Pollination that involves just one flower, flowers on the same plant, or flowers from two genetically identical plants is called self-pollination. • In contrast, pollination that involves two genetically different plants is called cross-pollination.

Section 2 Sexual Reproduction in Flowering Plants Chapter 30 Pollination, continued • Flower structure promotes self-pollination in plants that have flowers with petals that completely enclose both the male and female flower parts. • Pollen can be dispersed by water or air. The flowers of such wind-pollinated angiosperms are small and lack showy petals and sepals. • Successful wind pollination depends on four conditions: the release of large amounts of pollen, the ample circulation of air or water, proximity of other plants that it can pollinate, and dry weather.

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