Layers surrounding the ovum from outside to inside are:
A. Zona pellucida
B. Vitelline membrane
C. Corona radiata
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → C, A, B
C. Corona radiata — outermost. The ovum is released with a layer of follicle cells around it, the corona radiata.
A. Zona pellucida — middle. Inside the corona lies a non-cellular membrane, the zona pellucida. The sperm must cross it, helped by the acrosome’s enzymes.
B. Vitelline membrane — innermost. The vitelline membrane is the plasma membrane of the ovum itself. A narrow perivitelline space separates it from the zona pellucida.
NCERT Extract:
Fertilisation and Implantation – “… The secondary oocyte forms a new membrane called zona pellucida surrounding it. … During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum (Figure 2.10) and induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilise an ovum. The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane.”
Figure 2.10 Ovum surrounded by few sperms