This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Sex Hormones, Subject name: Physiology
[{'content': 'Upon contact between the sperm head and the zona pellucida, penetration of the sperm into the egg is allowed because of: \nSelect and explain. \nA. The acrosome reaction, B. The zona reaction, C. The perivitelline space, D. Pro nuclei formation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A. The acrosome reactionThe acrosome reaction causes a fusion of the plasma membrane and the acrosomal membrane of the sperm, with subsequent release of proteolytic enzymes that help the sperm enter the ovum. The zona reaction and Pro nuclei formation occur after the sperm has entered the ovum. Sperm enter the perivitelline space after penetration; there is no evidence that this space has any role in penetration. Cumulus expansion assists in movement of the sperm through the mass of granulosa cells for the sperm to get to the surface of the zona pellucida. However, the cumulus cells do not assist in actual penetration of the zona.', 'role': 'assistant'}]