6. With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
The diagram of 7- celled 8- nucleate embryo sac of plants is as follows:
The female gametophyte of plants is formed from a single functional megaspore with the help of four unequal mitotic divisions. These mitotic divisions give rise to 8 nuclei. Later, these nuclei assemble into 7 cells. To both chalazal and micropylar end three cells each move. The three cells at chalaza are called antipodal cells while those at micropylar end constitute egg apparatus. The egg apparatus includes two larger cells called synergid while the egg is the smallest cell that acts as a female gamete. Two nuclei migrate to the centre and together they form a single cell called the central cell. This central cell consists of two nuclei called polar nuclei. Thus, 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).