megagametophyte वाक्य
उदाहरण वाक्य
मोबाइल
- The genetic control of apomixis can involve a single genetic change that affects all the major developmental components, formation of the megagametophyte, parthenogenesis of the egg cell, and endosperm development.
- In flowering plants, the megagametophyte ( also referred to as the "'embryo sac "') is much smaller and typically consists of only seven cells and eight nuclei.
- In flowering plants, double fertilization occurs, which involves two sperm fertilizing the two gametes inside the megagametophyte ( the egg cell and the central cell ) to produce the embryo and the endosperm.
- Considerable confusion has resulted because diplospory is often defined to involve the megaspore mother cell only, but a number of plant families have a multicellular archesporium and the megagametophyte could originate from another archesporium cell.
- Fossil lycopod megaspores reaching 1 cm in diameter, and surrounded by vegetative tissue, are known ( Lepidocarpon, Achlamydocarpon ); these even germinate into a megagametophyte " in situ ".
- Within the megagametophyte one of the two sperm unites with the egg, forming a zygote, and the second sperm enters the central cell forming the endosperm mother cell, which completes the double fertilization process.
- Each pollen grain accordingly may be seen as a male plant in its own right; it produces a sperm cell and is dramatically different from the female plant, the megagametophyte that produces the female gamete.
- The egg producing gametophyte is known as a "'megagametophyte "', because it is typically larger, and the sperm producing gametophyte is known as a "'microgametophyte " '.
- It also should be borne in mind that every sexually reproducing extant species of vascular plant actually has an alternation of generations; the plants we see about us generally are megagametophytes ( the embryo sacs in the ovules ).
- These earliest ovules had the apical part of the nucellus exposed, from which there was a projection known as a lagenostome ( sometimes also called a salpinx ) that facilitated capture of the pollen and directed it down to the pollen chamber above the megagametophyte.
- Two sperm nuclei from a pollen grain ( the microgametophyte ), rather than a single sperm, enter the archegonium of the megagametophyte; one fuses with the egg nucleus to form the zygote, the other fuses with two other nuclei of the gametophyte to form'endosperm', which nourishes the developing embryo.
- In the families Lycopodiaceae and Huperziaceae, gametophytes are subterranean and mycotrophic, deriving nutrients from symbiosis with fungi . " Isoetes " and " Selaginella ", which are heterosporous, megagametophytes develop inside the megaspores, which crack open at the trilete suture to allow the male gametes to access the egg cells in the archegonia inside.
- Plants generally produce ovules of four shapes : the most common shape is called "'anatropous "', with a curved shape . "'Orthotropous "'ovules are straight with all the parts of the ovule lined up in a long row producing an uncurved seed . "'Campylotropous "'ovules have a curved megagametophyte often giving the seed a tight " C " shape.
- Seed maturity cannot be predicted accurately from cone flotation, cone moisture content, cone specific gravity; but the province of B . C . found embryo occupying 90 % + of the corrosion cavity and megagametophyte being firm and whitish in colour are the best predictors for white spruce in B . C ., and Quebec can forecast seed maturity some weeks in advance by monitoring seed development in relation to heat-sums and the phenological progression of the inflorescence of fireweed ( " Epilobium angustifolium"
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