Embryo Sac in Angiosperms

The embryo sac, also known as the megagametophyte, is a critical component of the seed in flowering plants (angiosperms). It is housed within the ovule and contains the female gametophyte, which plays a pivotal role in the reproductive process. Let’s delve into the components of the embryo sac and their functions:

1. Antipodal Cells:

   • Located at the chalazal end of the embryo sac.
   • Their precise function is not entirely understood, but they may play a role in nutrient storage or as a protective barrier.

2. Polar Nuclei:

   • Found at the center of the embryo sac.
   • They are essential for the process of double fertilization.

3. Egg Cell (Ovum):

   • Positioned near the micropylar end of the embryo sac.
   • It is the female gamete that fuses with the male gamete (sperm cell) during fertilization to form the zygote.

4. Synergid Cells:

   • Located near the egg cell.
   • They play a role in guiding the pollen tube to the embryo sac during fertilization.

5. Central Cell:

   • Also known as the secondary nucleus.
   • Contains two polar nuclei.
   • It fuses with a sperm cell during double fertilization to form the triploid endosperm, which nourishes the developing embryo.

6. Egg Apparatus:

   • Comprises the egg cell and synergid cells.
   • Facilitates the entry of pollen tubes into the embryo sac.

The structure and organization of the embryo sac are crucial for successful fertilization and seed development in flowering plants.

Certainly, let’s delve deeper into the structure and functions of the embryo sac, also known as the megagametophyte, in flowering plants (angiosperms):

1. Antipodal Cells:

   • These cells are typically three in number and are located at the chalazal end of the embryo sac, opposite the micropyle.
   • Their function is not fully understood, but they are believed to play a role in nutrient storage, embryo sac development, and possibly as a protective barrier.

2. Polar Nuclei:

   • The polar nuclei are two nuclei located at the center of the embryo sac.
   • They are involved in double fertilization, where one of the polar nuclei fuses with a sperm cell to form the primary endosperm nucleus (PEN), initiating the development of endosperm, which provides nourishment to the developing embryo.

3. Egg Cell (Ovum):

   • The egg cell is the female gamete located near the micropylar end of the embryo sac.
   • During fertilization, the egg cell fuses with a sperm cell to form the zygote, which develops into the embryo.

4. Synergid Cells:

   • Synergid cells are two cells located near the egg cell.
   • They have a role in guiding the pollen tube to the embryo sac during fertilization, facilitating the entry of the sperm cell to the egg cell.

5. Central Cell:

   • The central cell, also known as the secondary nucleus, is located centrally within the embryo sac.
   • It contains two polar nuclei, which fuse with a sperm cell during double fertilization.
   • The fusion of one polar nucleus with a sperm cell forms the triploid primary endosperm nucleus (PEN), which develops into the endosperm, a nutrient-rich tissue that supports the growing embryo.

6. Egg Apparatus:

   • The egg apparatus consists of the egg cell and synergid cells.
   • It plays a crucial role in the fertilization process by attracting and guiding the pollen tube to the embryo sac, ensuring successful sperm-egg fusion.

The embryo sac’s structure and cellular components are intricately involved in the reproductive process of angiosperms, ensuring successful fertilization, embryo development, and seed formation. Understanding these components and their functions sheds light on the complex mechanisms underlying plant reproduction.