Question

The arrangement of the nuclei in a normal embryo sac in the dicot plants is
A. 2+3+3
B. 3+3+2
C. 2+4+2
D. 3+2+3

Answer 1

Hint: The gametophyte in angiosperms is called the embryo sac. It is tiny and contains only a few (typically eight) nuclei; the cytoplasm is associated more or less directly with these nuclei and is not partitioned by cell walls.

Complete step by step answer: The embryo sac is the female gametophyte of angiosperms that consists of eight nuclei: the egg, short-lived synergids that are near the micropyle (A micropyle is the opening where the pollen nuclei will enter, two central nuclei which will combine with one of the pollen nuclei to form the endosperm) and three antipodal nuclei at the end of the embryo sac opposite to the micropyle. Like synergids, these nuclei degenerate shortly after fertilization. There are 2 synergids, in which each synergid contains one nucleus, and an egg cell also contains one nucleus in it. It is present in the micropyle along with synergid. The total number of nuclei at the micropyle is 3 nuclei. In the middle, the central cell is present which contains 2 polar nuclei. At the Chalazal end, three antipodals are present in which each antipodal contains one nucleus and the total count is 3 nuclei.
Hence, the correct answer is option D.

Note: Based on the number of megaspores, embryo sacs can be divided into three types: monosporic, diasporic and tetrasporic. In the monosporic embryo sac, meiosis of the diploid megaspore mother cell in the nucellus produces four haploid megaspores. In diasporic embryo sacs, meiosis produces only two megaspores, each containing two haploid nuclei, due to the absence of cytokinesis and cell plate formation following the second meiotic division.