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  • From an evolutionary point of view, retention of the female gametophyte with developing young embryo on the parent sporophyte for some time, is first observed in :  <div class='qna-

From an evolutionary point of view, retention of the female gametophyte with developing young embryo on the parent sporophyte for some time, is first observed in :
 

Option: 1

Liverworts
 


Option: 2

Mosses
 


Option: 3

Pteridophytes
 


Option: 4

Gymnosperms
 


Answers (1)

best_answer

 

 

 

  • The sporangia are formed singly in the axil of sporophylls which aggregate to form cones as in Selaginella and Equisetum or developed on the abaxial surface of leaves in groups called sori as in ferns like Dryopteris.
  • Sporangium may develop from a single cell (Leptosporangiate development) or from a group of cells (Eusporangiate development).
  • The spore mother cells in sporangia give rise to spores by undergoing meiosis.
  •  Pteridophytes can be homosporous or heterosporous. Homosporous pteridophytes produce similar kind of spores. Heterosporous pteridophytes produce two kinds of spores i.e. microspores and megaspores. Microspores develop into male gametophyte and megaspores develop into the female gametophyte.
  • Spores after germination give rise to a microscopic, usually photosynthetic, independent gametophytes known as Prothalli. 
  • Prothallus can be monoecious or dioecious in homosporous species but always dioecious in heterosporous species. 
  • Gametophytes have stalkless (sessile), jacketed multicellular sex organs. The male organ is antheridium and female organ is archegonium.
  • Antheridia give rise to biflagellate (Selaginella, Lycopodium) or multi flagellated (Dryopteris) male gametes.
  • Archegonium possesses jacket at the neck with four rows of jacket cells. Only one egg cell is present in the archegonium.
  • Fertilisation is by Zooidogamous Oogamy.
  • In some pteridophytes, the female gametophyte is retained in the megasporangium of the sporophyte. Fertilization and embryo development takes place in the sporangium itself. This event is considered as a precursor for seed habit.
  • The embryo develops into the sporophyte. 

 

 

From an evolutionary point of view, retention of the female gametophyte with developing young embryo on the parent sporophyte for some time, is first observed in heterosporous Selaginella (pteridophyte).

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shivangi.bhatnagar

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