(A) Draw the embryo sac of a flowering plant and label (i) central cell (ii) chalazal end of the embryo sac and (iii ) synergids.
(b) Name the cell that develops into the embryo sac and explain how this cell leads to the formation of embryo sac. Also mention the role played by the various cells of the embryo sac .

Explanation

(a)
(b) One of the nucellus cells develops into embryo sac . The process of formation of megaspores from the megaspore mother cell is called megasporogenesis . The nucleous of the funtional megaspore divides mitotically to form two nuclei which move to the opposite poles forming the 2 nucleate embryo sac. Again one more mitotic division results in the formation of 4 nucleate and later 8 nucleate stage of the embryo sac. Two nuclei present in central cell are called polar nuclei . Three cells grouped together at the microphar end constitute the egg apparatus and synergid . Three cells at the chalazal end are called the antipodals. A typical angiosperm embryo sac at maturity though 8 nucleate is 7 celled.