Question

A typical angiosperm embryo sac is 8-nucleate and
A. Single celled
B. Seven celled
C. Eight celled
D. Four celled

Answer 1

Angiosperms are the flowering plants that produce seeds covered in seed coat. They are the most diverse group of plants. The embryo sac is the female gametophyte is an oval structure. It is found in the nucleus of the ovule of flowering plants. It is formed by the division of the haploid megaspore nucleus and the site of fertilization of the egg and development of the embryo.

Complete answer:
The embryo sac is a large cell that builds in the ovule of flowering plants. It is similar to the female gametophyte of lower plants but it is very much reduced. It is produced by the division of the haploid megaspore nucleus.
The embryo sac is composed of six haploid cells that don’t have cell walls. Among these six cells, two are synergids, three are antipodal cells, and the remaining one is an egg cell. There are two haploid nuclei or polar nuclei are also present. Sometimes the two haploid cells fuse with polar nuclei and compose a single, endosperm mother cell. During fertilization, one male nucleus fuses with the egg nucleus and generates a zygote, later which turns into the embryo.
The female gametophyte or embryo sac produces from a single functional megaspore. This megaspore goes through three successive mitotic divisions and generates eight nucleate embryo sacs.
At the first mitotic division in the megaspore, two nuclei are produced. One of the two nucleus steps towards the micropylar end and the other nucleus steps towards the chalazal end. After that, these nuclei get divided at their respective ends. Later they divided once again and produced eight nucleate stages. After the complete division, there are four nuclei found at both ends that are four nuclei at the micropylar and four nuclei at the chalazal end of the embryo sac. In the case of the micropylar end, only three out of the four nuclei are divided into two synergids and one egg cell. These synergids and egg cells are together known as the egg apparatus. On the other hand, at the chalazal end, three out of four nuclei got divided into antipodal cells. The rest two cells i.e. one from the micropylar and one from the chalazal end, pass towards the centre, and they are known as the polar nuclei. These nuclei are located in a large central cell. Hence, finally, at the maturation level, the female gametophyte or embryo sac holds a seven-celled structure, but the number of nucleates present in it is eight.

Therefore, the correct option is option B.

Note: The embryo sac is a large cell which is an alternative name for female gametophyte. It is consisting of six haploid cells. This embryo sac is produced from a single functional megaspore, which goes through successive mitotic division. At its matured level, it possesses the structure of seven cells.