Question

Polar nuclei are located in
A. Pollen tube
B. Embryo sac
C. Ovule
D. Thalamus

Answer 1

Hint:In angiosperms, the female gametophyte has eight nucleated structures and seven celled structures. The female gametophyte is also known as the embryo sac. Female gametophyte develops in the ovary of the gynoecium.

Complete answer:Gynoecium produces megaspores and each megaspore produces a female gametophyte. Megaspore undergoes three successive mitotic divisions and forms eight nucleated embryo sacs. At maturity, it is a seven celled structure.
In the first mitotic division which is also known as equational division, two nuclei are formed. One moves towards the micropylar end and the other moves towards chalaza. On reaching the extreme ends in megaspore these nuclei divide at the respective ends.
The division is followed by re-division till the eight nuclei stage is attained.
At both the ends i.e. at the micropylar end and chalaza end four nuclei are present.
Two synergid cells are formed and one egg cell is formed at the micropylar end.
Two synergids and an egg cell from an egg apparatus.
Similarly, at the chalaza end, three nuclei are differentiated into antipodal cells.
One nucleus from the micropylar end and one nucleus from the chalaza end move towards the center of the embryo sac. These are called polar nuclei. Polar nuclei are located in the central cell of the female gametophyte.
Therefore at maturity female gametophyte i.e. embryo sac appears to be seven celled eight nucleated structures.
So, the correct answer to the given question is option B. Embryo sac.

Note: Polar nuclei on fusion with one of the nuclei of male gametophyte forms triploid endosperm. Egg cell from the egg apparatus on fusion with the male nucleus forms the zygote.