(a) From which end of the ovule, and how does the pollen tube gain its entry into the embryo sac of a Hibiscus flower ?

(b) State the fate of the male nuclei present in the pollen tube.

The correct answer is:
(a) From micropylar end, through the synergids (filiform apparatus) / filiform apparatus (within synergids) guides the entry of pollen tube.
(b) One male nucleus fuses with two polar nuclei to form Primary Endosperm Nucleus (PEN) and termed triple fusion, other male nucleus fuses with egg cell nucleus to form zygote i.e. undergoes Syngamy.

Step-by-Step Explanation:

Part (a): Entry of the Pollen Tube
In a Hibiscus flower, after pollination, the pollen grain germinates on the stigma to produce a pollen tube. This pollen tube grows down through the style and reaches the ovary, eventually entering the ovule. In most angiosperms like Hibiscus, the pollen tube enters the ovule through the micropylar end (a pore-like opening at the tip of the ovule). Within the embryo sac at the micropylar end, there is an egg apparatus consisting of an egg cell and two flanking synergids. The synergids possess special cellular thickenings called the filiform apparatus. The filiform apparatus plays a critical role in guiding the entry of the pollen tube into one of the synergids, facilitating the release of male gametes into the embryo sac.

Part (b): Fate of the Male Nuclei (Double Fertilization)
The pollen tube carries two male gametes (nuclei). Upon entering the embryo sac, these two male nuclei are released, leading to the process of double fertilization:
1. Syngamy: One of the male nuclei moves towards the egg cell and fuses with the egg cell nucleus. This fusion results in the formation of a diploid zygote, which eventually develops into the embryo.
2. Triple Fusion: The second male nucleus moves towards the central cell and fuses with the two haploid polar nuclei. Because this process involves the fusion of three haploid nuclei, it is termed triple fusion. The result of this fusion is the formation of a triploid Primary Endosperm Nucleus (PEN), which develops into the endosperm to provide nourishment to the growing embryo.