Embryo sac: Egg + 2 Synergids (micropylar end) + 3 Antipodal cells (chalazal end) + Central cell (2 polar nuclei)
Pollen tube guided by: Synergids (release chemoattractants)
Pollen tube enters one synergid → releases 2 sperm → double fertilisation
Answer: Synergids
Female gametophyte = embryo sac: develops from functional megaspore (after meiosis of megaspore mother cell in ovule). 7-celled, 8-nucleate structure. Micropylar end: egg apparatus (egg + 2 synergids). Chalazal end: 3 antipodal cells. Middle: central cell with 2 polar nuclei.
Pollen lands on stigma → germinates → pollen tube grows through style → enters ovule through micropyle → guided by synergid chemoattractants → enters one synergid → releases sperm → double fertilisation. Pollen tube carries vegetative nucleus at tip (which degenerates) and 2 sperm cells.
Sperm 1 + Egg = Zygote (2n) → Embryo. Sperm 2 + 2 Polar nuclei = Primary endosperm nucleus (3n) → Endosperm. Only angiosperms undergo double fertilisation. Gymnosperms have single fertilisation only.
After fertilisation: zygote → embryo (with suspensor). Endosperm nucleus → endosperm (food reserve). Ovule → seed. Ovary → fruit. Sepals/petals/stamens usually wither. Synergids and antipodals degenerate.
Megaspore mother cell meiosis produces four megaspores, of which only one survives. Three rounds of free nuclear mitosis then give eight nuclei, which organise into seven cells: one egg with two synergids at the micropylar end, three antipodal cells at the chalazal end, and one large central cell containing the two polar nuclei. Eight nuclei but seven cells, because the central cell holds two of them — this is the detail the question always turns on.
The synergids carry a specialised thickening of the cell wall at the micropylar end called the filiform apparatus. It secretes chemical signals that guide the pollen tube into the embryo sac and increases the surface area for absorption. The pollen tube enters through one synergid, not through the egg directly, and releases both male gametes there. Without the filiform apparatus the tube would have no directional cue.
The monosporic Polygonum type described above, in which one megaspore forms the whole sac, is by far the commonest and the one NCERT describes. Bisporic and tetrasporic types also exist, involving two and four nuclei respectively, but the exam expects the monosporic case unless it states otherwise. In all types the mature sac remains haploid throughout, because every division after meiosis is mitotic.
Saying eight cells instead of seven. There are eight nuclei but seven cells, because the central cell contains two polar nuclei.
Thinking the pollen tube enters the egg directly. It enters through a synergid, guided by the filiform apparatus, and discharges both gametes into it.