Answer:
Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma.
Animals require a digestive system because they take food in the form that body cannot directly utilize. The food needs to be broken down into form that body can utilize. Therefore digestive system becomes very important animals. There are various other organisms apart from animals that possess a digestive system For example amoeba has food vacuole that helps in digestion.