Final answer:
Bile salts are crucial for digesting fats and work by emulsifying them into smaller droplets in the duodenum, where enzymes like pancreatic lipase can effectively break them down. Option D is correct.
Step-by-step explanation:
Bile Salts and Fat Digestion
Bile salts play a crucial role in the digestion of fats. These salts are produced in the liver and stored in the gallbladder. When you consume food, particularly fats, bile salts are released into the duodenum, the first part of the small intestine.
In the duodenum, bile salts act to emulsify fats, which means they break down large fat droplets into smaller droplets. This process increases the surface area of the fats, allowing pancreatic lipase to more efficiently break the fats down. Emulsification by bile is important because it enables the fat molecules to become more accessible and susceptible to the action of digestive enzymes.
Therefore, the correct answer to the student's question is (d) fat in the duodenum. Bile salts do not act on proteins in the esophagus, gastrin, carbohydrates in the stomach, or fat in the stomach in the way described.