Question

8-nucleate embryo sac is
a. Monosporic
b. Bisporic
c. Tetrasporic
d. All the above

Answer 1

An Embryo sac represents the female gametophyte of a flowering plant. It consists of a thin-walled sac within the ovule that contains the egg nucleus and other nuclei that form endosperm on fertilization.

Complete answer:
Megaspore is a haploid structure that divides and gives rise to embryo sac which is also known as female gametophyte. Functional megaspore represents the first cell of the female gametophyte. The type of embryo sac development depends on the number of megaspores taking part in the development of embryo sac, a number of divisions occurring in the nucleus of the functional megaspore and the organization of nuclei in the mature embryo. There are three types of embryo sacs, monosporic, bisporic and tetrasporic.

In the monosporic embryo sac, out of the four megaspores, one megaspore at the chalazal end takes part in the formation of the embryo sac. Other three undergo programmed cell death. Nucleus undergoes three mitotic divisions to form 8 nuclei. This type is also called Polygonum type.
In the bisporic embryo sac, two megaspores take part in the formation of the embryo sac. The nucleus of two megaspores undergo two mitotic divisions and thus the resulting embryo sac is 8-nucleate.
In the tetrasporic embryo sac, all the four megaspores take part in the formation of the embryo sac. Here, the meiotic divisions in the megaspore mother cell are not followed by plate formation, so all the four haploid nuclei remain in a common cytoplasm and form a cone megaspore. The final structure of the embryo sac is 8-nucleate.
Thus, the 8-nucleate embryo sac can be monosporic, bisporic and tetrasporic.

So, the correct answer is option D.

Note: The mature embryo sac possesses 7 cells (3 antipodal cells, 2 synergid cells, 1 egg cell and 1 central cell) and 8 nuclei (3 of antipodal cell, 2 of synergid cells, 1 of egg cell and 2 of central cell).