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Pollen grains are not microspores, they are the male gametophytes produced when microspores undergo mitosis. Eggs are female gametes produced by the female gametophyte, they are not megaspores. Megaspores produce the female gametophyte through mitosis. Pollination of seed plants is not dependent on water at all, pollen grains are transported by wind and/or pollinating animals. When a male gametophyte is introduced to a female structure, it sticks to the stigma of the carpel. Once stuck to the stigma, the pollen grain germinates, it produces a pollen tube that extends down into the carpel's style and into the ovary. Sperm cells produced by the pollen grain then travel down through the pollen tube towards the ovules which contain the female gametophytes and gametes. If successful, fertilization occurs and a zygote starts to form, then more sperm cells are sent down the pollen tube where they combine with the nuclei of cells produced by the female gametophyte to form a polyploid endosperm nucleus which divides to form the endosperm.
Angiosperms produce both male and female gametophytes, which are produced by two different types of spores. The male gametophyte is produced through mitosis of microspores and female gametophyres are produced through the mitosis of megaspores. Every part of a flower is composed of modified leaves, the sporophylls (spore containing leaves) of the flower are the androecium (composed of all stamen) and gynoecium (composed of all carpels). The sporangia ( part of the sporophyte that undergoes meiosis to produce haploid spores) of the androecium are found within the anthers of the stamen. These sporangia produce microspores which undergo mitosis into haploid, male gametophytes, the male gametophyres undergo mitosis to produce male gametes. The spores produced by seed plants are not released, they develop into gametophytes attatched to the sporophyte. Male gametophytes are dependent on the sporophyte during development, but eventually separate from the sporophyte for pollination. The sporangia of the gynoecium are located in the ovary, in the ovules. Inside of the ovules, sporangia undergo meiosis to produce haploid megaspores, these megaspores undergo mitosis to produce haploid female gametophytes. Female gametophytes produce female gametes through mitosis. Unlike the male gametophytes, female gametophytes do not separate from the sporophyte.
Bryophytes do not depend on pollination, unlike angiosperms and gymnosperms ( seed plants) where the male gametophyte is carried via wind or pollinator to the gynoecium. Like seed plants, byrophytes produce haploid gametophytes through meiosis of diploid sporophytes, but the gametophyte is dominant in all three types of bryophytes. Byrophyte gametophytes have stuctures called gametangia, which contain gametes. Male gametangia are referred to as antheridia and contain male gametes, sperm. Female gametangia are called archegonia and each archegonium contains one female gamete. The archegonium is a flask shaped structure with the female gamete at the base, both the sperm and egg cells are surrounded by a protective layer of cells that do not participate in sexual reproduction. The gametophytes have characteristics that facilitate fertilization by causing sperm filled water drops to splash, sometimes this sperm rich water reaches the archegonia and fertilization occurs.
Like seed plants, the lycophyte sporophyte is dominant. Lycophyte gametophytes are usually free living, they don't depend on the sporophyte, but they are much smaller and short lived. Spores produced by the sporangia on the sporophyte are released, where they produce a free living, bisexual gametophyte plant called a prothallus.The prothallus contains both an antheridium which contains many flagellated sperm and an archegonium which contains a single egg. Water allows the flagellated sperm to swim from the antheridium to the archegonium where fertilization occurs. A diploid zygote will develop and will depend on the prothallus for nutrients, as the diploid plant matures and develops, the prothallus dies and a new sporophyte is produced.
If you do a quick Google search, you can easily find many diagrams and explanations of these sexual life cycles.
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