digestion is performed by the digestive system
gastric_digestion is not digestion. gastric_digestion is digestion. digestive_system is system. digestive_system is not system. digestive_system has liver_and_gallbladder digestive_tract is organ_system. digestive_tract is body_part. every_living_human_being has digestive_system digestive_system has do_with_food digestion is learning.