Question

Select the correct statement regarding the structure of a mature embryo sac
$1$. Egg apparatus is situated towards the chalazal end.
$2$. Antipodal cells are situated towards the micropylar end.
$3$. A typical angiosperm embryo sac is $7$ celled, $8$ nucleate at maturity.

A. $1$ only
B. $2$only
C. $3$only
D. $1$, $2$ and $3$

Answer 1

It is a female gametophyte of an angiosperms consisting of cells and nuclei. It looks like an oval structure that is present in the flowering plants. And then it is said to form a haploid megaspore nucleus. It has two haploid nuclei and six haploid cells and does not have a cell wall.

Complete answer:
The formation of the embryo sac takes place in two stages. Its first stage is megasporogenesis that occurs where the haploid of megaspore tetrad takes place due to the meiosis of the single diploid mother cell.
Then the second stage is megagametogenesis, in which the embryo sac is formed due to the mitosis process of the functional haploid megaspore that produces $8$ nucleate and also $7$ celled gametophyte. Then the polar nuclei is moved to the centre part in that all eight nuclei combine to form and also to generate a single diploid at the centre location.
After that the single diploid cell is then fused with the sperm to generate the triploid endosperm and the other three nuclei start to grow into antipodal cells, while two were modified into synergic cells which degenerate gradually. At the time of fertilization , one male nucleus and the egg nucleus are combined for the formation of the zygote that are leading to the development of the embryo.

Hence, the correct answer is option (C).

Note: The importance of angiosperms called the embryo sac are so tiny and also contain only a few nuclei, the cytoplasm is associated with more or less directly interacting with these nuclei that are not partitioned by the cell wall. One of the several nuclei of the embryo sac serves as an egg in the process of sexual reproduction.