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Double Fertilization:

  • Fertilization is a essential feature of angiosperms life-cycle.
  • The most common type of embryo sac i.e. polygonum type of embryo sac is formed from a monosporic (singlr nucleus) Megaspore by three successive mitosis divisions follwed by nuclear migration and cell wall formation giving rises to 7 celled, 8 nucleated embryo sac.
  • These cells includes - 3  antipodal cells(nutritive in function) at chalazal end, egg apparatus  at micropyle end (2 synergids for attracting male gametophyte &1 egg cell) and a  central cell formed by fusion of 2 polar nuclei, known as  secondary nucleus.
  • Of the 2 sperms in male gametophyte, one fertilizes the egg cell forming zygote(2n), and othe rfertilizes the secondary nucleus known as triple fusion forming Primary Endopserm Nucleus( 3n), which further divides to form endosperm which provides nutrition to developing embryo.
  • This entire phenomenon is known as double fertization in angiosperms.

therefore, doble fertilization includes:

  • Syngamy(2n) = Egg cell(n) + Spem fusion(n)
  • Triple fusion(3n)= Secondary nucleus(2n)+  another sperm(n).

 

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