The 'Cortical reaction' in the ovum, which prevents polyspermy (entry of multiple sperm), is triggered by:
A. The binding of the first sperm to the corona radiata
B. The fusion of the sperm head with the oocyte plasma membrane
C. The completion of meiosis II
D. The release of enzymes from the acrosome
Answer: Option B
Solution (By JKExamLibrary)
The cortical reaction is a mechanism to prevent polyspermy, ensuring that only one sperm fertilizes the egg. It is triggered immediately after the plasma membrane of the sperm fuses with the plasma membrane of the oocyte. This fusion causes a sudden release of calcium ions inside the oocyte, which triggers the cortical granules (located just beneath the oocyte membrane) to release their contents into the perivitelline space. These enzymes modify the zona pellucida (zona reaction), making it impermeable to other sperm.
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