In the embryo sac of certain angiosperms, the two polar nuclei of the central cell fuse just before the pollen tube discharges its male gametes into the synergid. What is the specific name and the ploidy of the structure that the second male gamete immediately fuses with in this condition?

Step-by-step solution

In a typical angiosperm embryo sac, the central cell contains two haploid polar nuclei. If these two polar nuclei fuse prior to fertilization (before the arrival of the male gametes), they form a single diploid structure known as the secondary nucleus. Consequently, the second male gamete will immediately fuse with this diploid secondary nucleus to form the triploid primary endosperm nucleus (PEN). Therefore, the target structure just before the male gamete fuses with it is the secondary nucleus, and its ploidy is