Correct Answer: D

Rationale: The correct answer is the amino group. Amino acids consist of an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain attached to a central carbon atom. The amino group is essential for the formation of proteins. The carboxyl group is not the base component but another important functional group in amino acids. Carbon chain and radicals are not specific chemical structures that form the base component of an amino acid.

Correct Answer: D

Rationale: The correct answer is D: portal blood system. After absorption, carbohydrates and proteins are transported via the portal blood system to the liver for further processing and distribution to the rest of the body. Choices A, B, and C are incorrect. Enterohepatic circulation refers to the recycling of compounds between the liver and the intestines, not the direct route for absorbed nutrients. Gastrointestinal circulation is a vague and non-specific term, not specifically related to the transport of absorbed nutrients. The common bile duct is involved in transporting bile from the liver and gallbladder to the small intestine, not the end products of carbohydrate and protein digestion.

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: A

Rationale: The correct answer is A: monosaccharides. When macronutrients like carbohydrates are digested, they are broken down into simpler forms. Carbohydrates are broken down into monosaccharides, proteins into amino acids, and fats into fatty acids. Therefore, the end products of carbohydrate digestion are monosaccharides. Choices B, C, and D are incorrect because polysaccharides are larger carbohydrate molecules, enzymes are not the end products of digestion but rather aid in the process, and cholesterol is not a direct end product of macronutrient digestion.

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.