Sites of Nutrient Digestion in the Alimentary Canal Steps: - Recall that chemical digestion begins in the mouth and stomach, continues in the small intestine (duodenum, jejunum, ileum), and is mostly complete by the ileum. - Identify carbohydrate digestion: starts with salivary amylase in mouth, continues with pancreatic amylase in duodenum, and finishes with brush border enzymes in jejunum/ileum. - Identify protein digestion: starts with pepsin in stomach, continues with pancreatic proteases in duodenum, and completes with intestinal peptidases in ileum. - Eliminate options based on incorrect locations or enzymes for each nutrient. Why C is correct: - Protein digestion is completed in the ileum, where intestinal enzymes like aminopeptidases fully break peptides into amino acids for absorption, as per the sequential enzymatic process in the small intestine. Why the others are wrong: - A: Carbohydrate digestion completes in the small intestine (jejunum/ileum), not the colon, which mainly absorbs water. - B: Humans lack enzymes to digest cellulose (a plant fiber); the duodenum focuses on fats, proteins, and carbs, not cellulose. - D: The stomach secretes pepsin for proteins, not …