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Mosses: Structures involved
• What you associate with mosses is a gametophyte
• Gametophytes are haploid
Mosses: Development/ Growth
• Mitosis occurs producing a diploid sporophyte• Sporophyte remains attached to the
gametophyte– Diploid – Sporophyte cannot feed itself, but is genetically
different than the gametophyte
Mosses: The next generation…
• Diploid sporophyte produces cells that undergo meiosis; this produces haploid organisms, or gametophytes.
Ferns: Structures involved
• What you associate with ferns is the sporophyte• Sporophyte grows from gametophyte• Gametophytes are tiny (10 mm)
– Antheridium– Archegonium
Ferns: Development/ Growth
• Mitosis occurs producing a diploid sporophyte with fronds
• Sporophyte remains attached to the gametophyte, crushing it as it increases in size
Ferns: The next generation…
• Specialized cells, usually on the underside of the fronds, undergo meiosis and produce spores.
Conifers: Fertilization
• Typically the conifers much reach maturity before they can reproduce sometimes up to 30 years.
• Conifers can reproduce without water for the sperm to swim in.
• Sexual reproduction can actually take years
Ovule: female sex cell
– One large diploid megaspore mother cell undergoes meiosis and produces 4 haploid megaspores
Ovule: female sex cell
– Remaining mega spore undergoes three mitotic divisions to produce 8 haploid nuclei
Ovule: female sex cell
– Two nuclei move to the center of the cell while the remaining 6 move to the polar ends- three to each side
Ovule: female sex cell
– Cell walls form around the 6 nuclei at the ends
– One of these 6 cells becomes the egg, (the others die at fertilization)
– Embryo sac consists of 7 cells and 8 nuclei- this is the mature female gametophyte
Pollen: male sex cell– Microspore mother cells undergo meiosis and produces 4 haploid microspores, each of which undergoes mitosis to form two haploid cells
Pollen: male sex cell
– Wall develops around microspores and the two celled structure is a pollen grain- this is the mature male gametophyte
Pollen: male sex cell
– The larger cell will produce the tube cell containing the tube nucleus.• When attached, the tube nucleus will make a pollen tube
– The smaller cell is the generative cell• It will undergo yet another mitotic division to produce
two sperm
Flowering plants: Fertilization (Double
Fertilization)• Pollen tube grows from pollen (takes about a day)
Flowering plants: Fertilization (Double Fertilization)
• The two cells produced from the generative cell enter the ovule through the pollen tube– One of the sperm fuses with the egg to
form a diploid zygote• This will be the embryo
Flowering plants: Fertilization (Double Fertilization)
• The two cells produced from the generative cell enter the ovule through the pollen tube– The other sperm fuses with the two nuclei in the megaspore to produce a triploid nucleus.
• This will be the endosperm- the nutrients contained within a seed so that the embryo has energy to remain alive and begin the growth process
Flowering plants: Seed germination• Seeds can remain dormant for many years• When the conditions are right, the seed will
germinate
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