[Campbell Biology P.954] In what sense are nutrients from a recently ingested meal not truly... | Practice Question

In what sense are nutrients from a recently ingested meal not truly "inside" an animal's body prior to the absorption stage?

  • A: The digestive tract is considered external to the body's internal environment until absorption occurs, passing substances across a membrane into the body proper.
  • B: Nutrients are only "inside" once they are fully broken down into their smallest molecular forms, regardless of their location.
  • C: The body's immune system recognizes undigested food as foreign, hence it's not truly internal.
  • D: Absorption is a passive process that doesn't fully integrate nutrients into body tissues.

Explanation

The digestive tract, from mouth to anus, is essentially a tube passing through the body. Its lumen is continuous with the outside environment. Nutrients are only considered 'inside' the body when they are absorbed across the epithelial lining of the digestive tract and enter the circulatory or lymphatic system, thereby becoming part of the body's internal fluid environment.