Final answer:
The brain is the organ not involved in digestion, as it does not process food but instead controls bodily functions and cognitive processes. Hence, option (d) is correct.
Step-by-step explanation:
The organ not involved in digestion among the options provided is the brain. While the liver, stomach, and pancreas play direct roles in the digestive process, the brain does not process food for digestion. The liver produces bile crucial for fat emulsification, the stomach secretes digestive enzymes and acids to break down food, and the pancreas produces digestive enzymes for the small intestine.
However, the brain's primary functions are related to controlling bodily functions and cognitive processes rather than digestion. The brain is a complex organ that plays a central role in controlling and coordinating various functions of the body.