Animals posses nerve networks or nervous systems to respond to their environment. But the single celled Amoeba does not possesses any nerve cell, so how it come to know whether a particle it encounters is gain or sand and not its dinner

Animals possess nerve or nervous systems to respond to their environment. But the single celled amoeba does not possesses any nerve cell , so, how it come to know whether a particle it encounters is a grain of sand and not its dinner by /