Ovum Layers — Corona Radiata, Zona Pellucida, Perivitelline Space, Plasma Membrane
✅ Asked in NEET 2026Arrange the cell layers/structures around the female gamete from outer to inner: A. Zona pellucida, B. Perivitelline space, C. Corona radiata, D. Plasma membrane of ovum.
Arrange the cell layers/structures around the female gamete from outer to inner: A. Zona pellucida, B. Perivitelline space, C. Corona radiata, D. Plasma membrane of ovum.
Answer & NCERT explanation
Correct answer: C — C, A, B, D
From outer to inner: corona radiata (C) -> zona pellucida (A) -> perivitelline space (B) -> plasma membrane of ovum (D).
Read more NCERT concept on the PYQ
Can you think of any advantage for this? Does the first polar body born out of first meiotic division divide further or degenerate? At present we are not very certain about this. The tertiary follicle further changes into the mature follicle or Graafian follicle. The secondary oocyte forms a new membrane called zona pellucida surrounding it. The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation. Can you identify major differences between spermatogenesis and oogenesis?
The mature female gamete (secondary oocyte/ovum) is surrounded by several layers, arranged FROM OUTSIDE TO INSIDE as follows: (1) CORONA RADIATA — outermost crown of follicular cells. (2) ZONA PELLUCIDA — a thick glycoprotein membrane secreted by the secondary oocyte itself; the species-specific sperm-binding layer. (3) PERIVITELLINE SPACE — narrow fluid-filled gap between the zona pellucida and the ovum's plasma membrane. (4) PLASMA MEMBRANE OF OVUM (oolemma) — the innermost true cell membrane. The tertiary follicle matures into the Graafian follicle, and the Graafian follicle ruptures to release the secondary oocyte by OVULATION.
Memory order from OUTER → INNER: Corona → ZP → Perivitelline → Plasma membrane (C → Z → P → P). NEET 2026 directly tested this sequence. Functional logic: corona radiata supplies nutrients; zona pellucida mediates species-specific sperm recognition and the block to polyspermy; perivitelline space accumulates the second polar body; plasma membrane is the sperm-egg fusion site. Don't confuse zona pellucida (oocyte layer) with chorion (embryonic membrane).
Order from outer to inner: zona pellucida → corona radiata → plasma membrane → perivitelline space.
Order from outer to inner: CORONA RADIATA → ZONA PELLUCIDA → PERIVITELLINE SPACE → PLASMA MEMBRANE of ovum.
Outside-in: Corona (cells), Zona (glycoprotein coat), Perivitelline (space), Plasma membrane (oolemma). C-Z-P-P.
- Order outer → inner: Corona radiata → Zona pellucida → Perivitelline space → Plasma membrane of ovum.
- Zona pellucida is a thick glycoprotein membrane secreted by the secondary oocyte itself.
- Graafian follicle = mature tertiary follicle; ruptures to release secondary oocyte → ovulation.
- First polar body fate is uncertain (may divide further or degenerate) — NCERT explicitly states this.
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