UPSC CDS 2 2023 GK Paper

Concept:The nucellus is the only diploid ($2n$) tissue in the angiosperm ovule; synergids, egg, and antipodals are all haploid ($n$) cells of the embryo sac.Explanation:In angiosperms, the ovule contains the nucellus (a mass of sporophytic tissue) and the embryo sac (female gametophyte).The nucellus is part of the parent sporophyte, so its cells are diploid ($2n$).It surrounds and provides nourishment to the developing embryo sac.The embryo sac is formed from a megaspore mother cell after meiosis.The megaspore mother cell undergoes meiosis to produce four haploid megaspores; one survives and develops into the embryo sac.The mature embryo sac typically contains seven cells: one egg cell, two synergids, three antipodal cells, and a central cell with two polar nuclei.All these cells (except the central cell which is $2n$ after fusion) are haploid ($n$).Thus, synergids ($n$), egg ($n$), and antipodals ($n$) are all haploid cells.Only the nucellus is not haploid; it is diploid ($2n$).Answer:A. Nucellus