This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'Ion responsible to prevent polyspermy at the time of feilization in mammals is - \nSelect and explain. \nA. Na, B. K, C. Ca, D. Mg', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans. is 'c' i.e., Ca Only one sperm can enter into oocyte, and fuher entry of sperms is prevented by the activation of ovum. Fusion of membranes of the gametes (sperm and ovum) leads to ovum activation which involves following events:- Membrane potential of ovum decreases (depolarization). Release of calcium ions from intracellular egg reserve leads to exocytosis of coical granules into the perivitelline space. The spread of coical granules along perivitelline membrane prevents fuher entry of sperm into the ovum. This is called vitelline block to polyspermy.", 'role': 'assistant'}]