Which organ is involved in ingestion

The mouth is the organ involved in ingestion in the digestive system.

Explanation:

Intake of food into the mouth and break down into small pieces there, is the process of the ingestion. In the ingestion process food is taken into the mouth and crushed and broken down into smaller pieces with the help of teeth. The presence of food triggers nervous reflexes to cause the salivary glands to release a fluid saliva. Saliva also softens and provides moisture to the food in the mouth to make it easier to swallow down to esophagus. It helps in digestion of starches to begin, present in food.