One Sperm Fertilizes the Egg; Polyspermy Is Actively Blocked
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Once one sperm fuses with the egg, per Bio 3341, the egg triggers a rapid membrane change blocking further sperm, preventing polyspermy.
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The fertilizing sperm's entry triggers egg-surface changes that alter the membrane within seconds.
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"Fertilization takes many sperm," per Bio 3341, ignores this block keeping fertilization to one sperm.