Which substance is stored in the gallbladder and aids in fat digestion?

The correct choice is bile, as it is the substance specifically stored in the gallbladder and plays a crucial role in the digestion of fats. Bile is produced by the liver and then concentrated and stored in the gallbladder until it is needed in the digestive process. When fatty foods enter the small intestine, the gallbladder releases bile, which contains bile salts that emulsify fats. This emulsification process breaks down large fat globules into smaller droplets, making it easier for digestive enzymes to further break down fats for absorption into the body.

This function is unique to bile in the context of fat digestion, whereas the other substances listed do not serve the same role in this specific process. Hydrochloric acid is involved in the stomach for protein digestion and creating an acidic environment, pancreatic fluid contains various enzymes for digesting carbohydrates, proteins, and fats, but is not stored in the gallbladder, and saliva primarily aids in the initial stages of digestion through enzymes that break down carbohydrates.