Biology · Human Reproduction · NEET
The antrum appears at the TERTIARY follicle stage, NOT the secondary one. NCERT says the secondary follicle 'soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum'. This is a very common NEET trap: many students wrongly link the antrum to the secondary follicle.
A secondary follicle has more layers of granulosa cells and a new theca, but NO antrum. A tertiary follicle has the fluid-filled antrum, and its theca splits into an inner theca interna and outer theca externa. So the antrum is the key marker that separates secondary from tertiary.
They are closely linked but not the same. The tertiary follicle changes into the mature follicle, called the Graafian follicle. In the Graafian follicle the secondary oocyte forms a new membrane called the zona pellucida. The Graafian follicle then ruptures at ovulation to release the secondary oocyte.
At the tertiary follicle stage. NCERT clearly states that it is at the tertiary follicle stage that the primary oocyte grows in size and completes its first meiotic division. This forms a secondary oocyte and the first polar body.
A primary follicle is a primary oocyte surrounded by a single layer of granulosa cells. It forms early: oogonia become primary oocytes (arrested in prophase-I), and each primary oocyte gets wrapped by one layer of granulosa cells to become a primary follicle. At puberty only about 60,000 to 80,000 primary follicles are left in each ovary.
The single theca first appears at the secondary follicle stage. It then gets organised into an inner theca interna and an outer theca externa at the tertiary follicle stage, when the antrum is present.
Given below are two statements regarding oogenesis. Statement I: The primary follicles get surrounded by more layers of granulosa cells, a theca and shows fluid filled cavity antrum. Now it is called secondary follicle. Statement II: Graafian follicle ruptures to release the secondary oocyte from the ovary by the process called ovulation. In the light of the above statements, choose the correct answer:
Match Column-I with Column-II: a. Mons pubis, b. Antrum, c. Trophectoderm, d. Nebenkern with (i) Embryo formation, (ii) Antrum, (iii) Female external genitalia, (iv) Graafian follicle.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Primary follicle to secondary follicle to tertiary follicle to Graafian (mature) follicle. The Graafian follicle then bursts at ovulation to release the secondary oocyte.
The secondary oocyte forms a new membrane called the zona pellucida around itself at the Graafian follicle stage, just before ovulation.
A primary follicle has just a single layer of granulosa cells around the primary oocyte. More layers are added as it becomes a secondary follicle.
A secondary oocyte is released at ovulation. NCERT often calls it the ovum, but strictly it is a secondary oocyte that has not yet finished meiosis-II. Meiosis-II completes only when a sperm enters.
NEET repeatedly tests the exact stage where the antrum and theca layers appear (2016, 2023) and links follicles to ovulation and hormones. One or two marks almost every year depend on knowing that antrum equals tertiary, not secondary.
