Where does the absorption of most nutrients occur?

Correct Answer: B

Rationale: The absorption of most nutrients occurs in the small intestine. This is where digested food is broken down further and absorbed into the bloodstream through the intestinal walls. The large intestine primarily absorbs water and electrolytes, while the stomach mainly aids in digestion by breaking down food with gastric juices. The mouth is responsible for the initial mechanical breakdown of food through chewing and the enzymatic action of saliva, but absorption does not occur there.

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: C

Rationale: The correct answer is H. pylori. This bacterium is known to be associated with the development of peptic ulcers and an increased risk of gastric cancer. Lactobacillus (Choice A) and Bifidobacterium (Choice B) are probiotic bacteria that are beneficial to human health and not associated with causing these conditions. E. coli (Choice D) is a diverse group of bacteria, some of which can be pathogenic, but they are not primarily linked to peptic ulcers and gastric cancer like H. pylori.

Correct Answer: A

Rationale: The correct answer is pinocytosis. Pinocytosis is a process where cells in the small intestine absorb nutrients by engulfing them. This process is different from phagocytosis, which involves engulfing large particles, and excretion, which is the removal of waste products. Electrochemical diffusion is not directly involved in the absorption of food in the small intestine.

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.