Q.The correct order of haploid, diploid and triploid structure in fertilized embryo sac is

In the commonest, monosporic (Polygonum-type) pattern, the single surviving functional megaspore - the first cell of the embryo sac - elongates along the micropylar-chalazal axis and its nucleus divides mitotically without any wall forming; a large central vacuole then appears between the daughter nuclei and pushes them to opposite poles, where each divides twice more, purely by free nuclear division (no walls), to give four nuclei per pole and eight nuclei sharing one cytoplasm. Only after this last division does the sac-shaped cell undergo cellular organisation. At the micropylar end, three of the four nuclei form an egg apparatus - a central egg cell flanked by two synergids, each bearing a filiform apparatus that helps conduct nutrients from the nucellus and chemically guides the incoming pollen tube - while the fourth micropylar nucleus stays free as the upper polar nucleus. At the chalazal end, three nuclei form three antipodal cells and the fourth becomes the lower polar nucleus; the two polar nuclei may remain separate or fuse into a single secondary nucleus of the central cell. The finished structure - …