Megasporogenesis MCQ - Practice Questions with Answers

Megasporogenesis:

• In the hypodermal region of the nucellus towards the micropylar end, a primary archesporial cell develops.
• It divided to form an outer primary parietal cell and an inner primary sporogenous cell.
• The primary sporogenous cell functions as diploid megaspore mother cell or megasporocyte.
• The megaspore mother cell divides meiotically to form four haploid megaspores. 
• The megaspore towards the chalazal end remains functional while the rest three of them degenerate. 

Megagametogenesis:

• The functional megaspore enlarges and undergoes three mitotic divisions in which only the karyokinesis occurs.
• Hence, 8 nuclei are formed with common cytoplasm. 
• This method of embryo sac formation from a single megaspore is termed monosporic development. 

Female Gametophyte or Embryo sac:

• After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac.
• Three cells are grouped together at the micropylar end and constitute the egg apparatus. 
• The egg apparatus, in turn, consists of two synergids and one egg cell.
• The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.
• Three cells are at the chalazal end and are called the antipodals. 
• The large central cell has two polar nuclei.
• Thus, a typical angiosperm embryo sac, at maturity, though 8-nucleate is 7-celled.