The vitelline layer of animal eggs has species-specific protein receptors that match proteins on the sperm’s outer surface.
These receptors prevent
Select Optionfertilization of the egg by the sperm of another speciessecondary fertilization by additional sperm
, which is especially important in species that practice external fertilization. Once a sperm whose proteins match these receptors has penetrated the vitelline layer, its membrane fuses with the egg's. This fusion triggers the vitelline layer to harden and separate from the egg plasma membrane, preventing
Select Optionfertilization of the egg by the sperm of another species.secondary fertilization by additional sperm.