Completion of the first meiotic division of the primary oocytes takes…

The correct answer is Option (2) → Within the tertiary follicle

The primary oocyte stays stopped in prophase I from foetal life. It completes the first meiotic division inside the tertiary follicle, giving a large secondary oocyte and a tiny first polar body. Q25 of this paper asks the same point.

Option (1) When acrosomal secretion of the sperm enters zona pellucida of the ovum — Incorrect. Sperm entry completes the second meiotic division, of the secondary oocyte, not the first.

Option (2) Within the tertiary follicle — Correct. The first division is completed in the tertiary follicle, before ovulation.

Option (3) When the ovum reaches the ampullary region of the fallopian tube — Incorrect. What reaches the ampulla is already a secondary oocyte; the first division is over by then.

Option (4) During copulation — Incorrect. Copulation only places sperms in the vagina; it does not act on the oocyte.

NCERT Extract:
Gametogenesis – “… The primary follicles get surrounded by more layers of granulosa cells and a new theca and are called secondary follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. It is important to draw your attention that it is at this stage that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body (Figure 2.8b).”

Figure 2.8 Schematic representation of (a) Spermatogenesis; (b) Oogenesis