Biology · Human Reproduction · NEET
From outermost to innermost: corona radiata, then zona pellucida, then perivitelline space, then the plasma membrane of the ovum. NCERT lists the secondary oocyte surrounded by the zona pellucida, with the corona radiata (granulosa cells) lying outside it. NEET has directly asked this order, so learn it as C, A, B, D style sequence (Corona, Zona, Perivitelline space, Plasma membrane).
The corona radiata is the OUTER covering made of granulosa (follicular) cells, so it is cellular. The zona pellucida lies INSIDE the corona radiata and is a clear, non-cellular glycoprotein layer. This is important for NEET because the sperm-binding receptors are on the zona pellucida, not on the corona radiata.
On the zona pellucida. During fertilisation the sperm first contacts the zona pellucida, which carries the receptors for sperm binding and then triggers changes that block polyspermy. This was asked directly in NEET 2021, so the answer is zona pellucida, not corona radiata, perivitelline space or vitelline membrane.
The zona pellucida is a NON-CELLULAR, transparent glycoprotein layer. It is not made of cells, unlike the corona radiata which is a layer of granulosa cells. NEET often traps students by hinting it is a cell layer — remember it is a non-living membrane-like coat.
At ovulation the secondary oocyte released from the Graafian follicle is surrounded by the zona pellucida (external to the plasma membrane), with the corona radiata outside that. In a single-answer NEET question the expected answer is the zona pellucida. It is not the endometrium (uterus lining) or the chorion (an extra-embryonic membrane).
Arrange the following cell layers/structures around the female gamete, from outer to inner side: A. Zona pellucida B. Perivitelline space C. Corona radiata D. Plasma membrane of ovum
Receptors for sperm binding in mammals are present on
The covering of the ovum at ovulation is _________.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the thin fluid-filled gap between the zona pellucida and the plasma membrane of the ovum. In the outer-to-inner order it sits third: corona radiata, zona pellucida, perivitelline space, plasma membrane.
The corona radiata is made of granulosa (follicular) cells that stay attached around the released oocyte. They come from the follicle but travel with the ovum as its outermost covering after ovulation.
The acrosome at the sperm head releases enzymes that help the sperm pass through the corona radiata and the zona pellucida. Contact with the zona pellucida then causes changes that stop other sperm from entering (block to polyspermy).
No. In NEET questions 'zona radiata' is usually a distractor. The correct clear non-cellular covering of the human ovum is the zona pellucida; corona radiata is the separate outer cell layer.
