A) a single haploid nucleus
B) one diploid and one haploid nuclie
C) two haploid polar nuclei
D) one diploid secondary nucleus
Correct Answer: C
Solution :
A fully developed typical orpolygonum type of embryo sac is large and oval structure consisting of seven cells and eight nuclei. [a] Egg apparatus : This is a group of 3 cells situated at the micropylar end. The centrally located cell is called egg cell. On its sides are present two synergids. Egg cell has a large vacuole at its upper end and a prominent nucleus near its lower end. Synergids show a filiform apparatus attached to their upper wall. It is known to attract and guide the pollen tube. Each of the synergids has a vacuole at its lower end and the nucleus at its upper end. [b] Polar nuclei : These are situated in the centre of the embryo sac representing a large binucleate central cell. Generally, both the polar nuclei fuse before fertilization and form a single diploid nucleus called secondary nucleus or definitive nucleus. [c] Antipodals : The three cells situated at the chalazal end are called antipodals. These cells generally degenerate soon after fertilization. On going to double fertilization the second male gamete fuse with secondary nucleus to form primary endosperm nucleus (3n).
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