Final answer:
The colon is the organ in the GI tract that is primarily responsible for absorbing water and ions, converting liquid chyme into semisolid feces while maintaining fluid balance in the body.
Therefore, the correct answer is: option "the colon".
Step-by-step explanation:
The organ of the gastrointestinal (GI) system that absorbs water and ions is the large intestine, specifically the colon.
The colon processes food, with the help of healthy bacteria, that was not digested by the small intestine. The colon aborbs water, minerals, and vitamins from the food. Finally, the colon forms and stores feces.
Although water and lipids are absorbed throughout the small intestine, including the duodenum and ileum, it's the large intestine, particularly the colon, where significant water reabsorption and mineral salts take place.
The small intestine, including the ileum, absorbs about 90 percent of water ingested, with most of the remaining water being absorbed by the large intestine.
The colon converts the liquid chyme residue into semisolid feces and absorbs mineral salts that aid in this process. The absorbent nature of the colon is essential for maintaining the body's fluid balance and preventing dehydration.