Question

Explain the development of female gametophyte in angiosperm by a well-labeled diagram only.

Answer 1

Hint: The group of plants, which produce flowers and whose seeds are covered by an outer covering is known as Angiosperms. The female gametophyte is a sexual organ of the flower and is typically developed within the ovule.

Complete answer:
The process of development of the female gametophyte starts from a structure called the female megaspore. The female gametophyte also known as the megagametophyte can also be called the embryo sac. This occurs inside the ovule or the megasporangium. The process of formation is through a series of continuous cell division. Within the ovule, a primary cell known as the archesporial cell is present right below the epidermis and at the end of the nucellus. The cell undergoes the first division into an inner primary sporogenous cell and an outer primary parietal cell. The sporogenous cell is the one that gets developed into the megaspore mother cell. The mother cell undergoes mitosis or equational division to produce four megaspores. From the group of four cells, only one cell survives, while the rest of the cells degenerate. The surviving cell is known as the functional megaspore.

The development of the gametophyte is then initiated from the functional megaspore. Four daughter cells are produced from this structure by the process of meiosis, which is the reduction division. Thus the daughter cells formed are haploid. And the arrangement of these cells is known as a linear tetrad. Out of the four, three of the cells are present at the micropylar end of the ovule, and they undergo degeneration, while the one cell present in the chalazal end turns functional. The remaining one functional cell gets converted to the female gametophyte or the embryo sac.

The gametophyte thus formed is seven celled and eight nucleated. The egg cell along with two synergid cells are present at the micropylar end, while three antipodal cells are present at the chalazal pole, and the large cell enclosing is known as the central cell and consists of the polar nuclei.

Note: In angiosperms, there occurs the production of both male and female gametophytes. Like embryo sac which is the female gametophyte, the male gametophyte is represented by the pollen grain, which is developed from the microspore mother cell, and initiated by a process known as the microsporogenesis.