Which part of the digestive system is responsible for the mechanical digestion of food?

Correct Answer: B

Rationale: The correct answer is B: stomach. The stomach is responsible for mechanical digestion through the churning and mixing of food with gastric juices, breaking it down into smaller particles. The mouth initiates digestion by chewing and mixing food with saliva, but it primarily focuses on chemical digestion through enzymes. The small intestine is where most of the chemical digestion and nutrient absorption occur, not mechanical digestion. The large intestine's main function is water absorption and the formation of feces, not mechanical digestion. Therefore, the stomach is the correct choice for mechanical digestion in the digestive system.

Correct Answer: C

Rationale: The correct answer is C: Liver. The liver produces bile, which plays a crucial role in digestion by breaking down fats. The pancreas (A) produces digestive enzymes, not bile. The gallbladder (B) stores bile produced by the liver but does not produce it. The stomach (D) produces gastric juices, not bile. Therefore, the liver is the only organ that produces bile, making it the correct answer.

Correct Answer: B

Rationale: The correct answer is B because the small intestine is primarily responsible for absorbing nutrients from digested food. It has specialized structures like villi to maximize nutrient absorption. Choice A is incorrect as the pancreas and other organs produce digestive enzymes. Choice C is incorrect as the liver produces bile. Choice D is incorrect as waste is stored in the large intestine, not the small intestine.

Correct Answer: C

Rationale: The correct answer is C: CCK. Cholecystokinin (CCK) is a hormone released by the small intestine in response to the presence of fatty acids and amino acids. It stimulates the release of bile from the gallbladder and increases bile production by the liver cells to aid in digestion. Sympathetic activation (choice A) typically inhibits digestive functions. Secretin (choice B) primarily stimulates pancreatic bicarbonate secretion, not bile production. Bile salts (choice D) are products of bile, not direct stimulators of bile production. Therefore, CCK is the correct choice as it directly influences the production of bile by the liver cells.

Correct Answer: D

Rationale: The correct answer is D: Mainly found in the colon. Intestinal flora, also known as gut microbiota, is primarily located in the colon. This is because the colon provides an ideal environment for the growth and survival of the diverse array of beneficial bacteria that make up the intestinal flora. These bacteria play a crucial role in various physiological functions, such as digestion, immune system regulation, and vitamin production. Choices A, B, and C are incorrect because intestinal flora are predominantly bacteria (not viruses), are not solely located in the duodenum but throughout the gastrointestinal tract, and are essential for normal digestion, not just needed.