Correct Answer: A

Rationale: The parotid, submandibular, and sublingual glands are the main salivary glands located in the mouth. They play a crucial role in producing saliva, which aids in digestion. The stomach (choice B) is where gastric juices are produced, the pancreas (choice C) secretes digestive enzymes into the small intestine, and the duodenum (choice D) is the first part of the small intestine where most chemical digestion occurs. Therefore, the correct answer is the mouth (choice A) as it is where these salivary glands are situated.

Correct Answer: D

Rationale: The correct answer is Glycine. Glycine is indeed one of the simplest amino acids as it consists of just a hydrogen atom as its side chain. Arginine, Valine, and Lysine are all more complex amino acids compared to Glycine, making them incorrect choices for this question.

Correct Answer: D

Rationale: Gas formation in the colon is primarily due to bacterial fermentation of undigested carbohydrates. Choice A, consuming refined foods, is incorrect as gas formation is not directly linked to refined foods but rather undigested carbohydrates. Choice B, drinking excess water, is incorrect as water consumption does not lead to gas formation in the colon. Choice C, swallowing air while eating, is incorrect as this may cause belching but not gas formation in the colon. The correct answer is D because bacterial action on organic compounds, specifically undigested carbohydrates, leads to gas production in the colon.

Correct Answer: C

Rationale: The correct answer is C: water. Water is the main component of blood plasma, interstitial fluid, and intracellular fluid. It plays a crucial role in various bodily functions, including transporting nutrients, regulating body temperature, and maintaining cell structure. Choices A, B, and D are incorrect because while potassium, sodium, and calcium are essential electrolytes found in the body, they are not the main constituents of these fluids as water is.

Correct Answer: A

Rationale: Mucus is produced by the salivary glands to moisten food and aid in swallowing. Additionally, the intestinal glands secrete mucus to protect the lining of the intestines. The other choices, esophageal glands, pineal gland, and islets of Langerhans, are not involved in the production of mucus in the digestive system.