Disaccharide not digested in intestine is –
**Core Concept**
The question is testing the ability to identify a disaccharide that is not digested in the intestine. This requires knowledge of carbohydrate digestion and absorption in the gastrointestinal tract. Disaccharides are simple sugars composed of two monosaccharides linked together, and they are typically digested by enzymes in the small intestine.
**Why the Correct Answer is Right**
The disaccharide lactulose is not digested in the intestine because it is not broken down by any of the enzymes present in the small intestine, such as sucrase, maltase, or lactase. Lactulose is a synthetic disaccharide composed of galactose and fructose molecules, and it is not a natural substrate for any of the intestinal disaccharidases. As a result, lactulose is not absorbed in the intestine and is instead fermented by colonic bacteria, producing short-chain fatty acids and gas.
**Why Each Wrong Option is Incorrect**
**Option A:** Maltose is a disaccharide composed of two glucose molecules, and it is broken down by the enzyme maltase in the small intestine. Therefore, maltose is digested in the intestine.
**Option B:** Sucrose is a disaccharide composed of glucose and fructose molecules, and it is broken down by the enzyme sucrase in the small intestine. Therefore, sucrose is digested in the intestine.
**Option C:** Lactose is a disaccharide composed of glucose and galactose molecules, and it is broken down by the enzyme lactase in the small intestine. However, lactose intolerance is a common condition in which lactase activity is deficient, leading to undigested lactose in the intestine.
**Clinical Pearl / High-Yield Fact**
Lactulose is often used as a laxative to treat constipation because it is not digested in the intestine and is instead fermented by colonic bacteria, producing gas and promoting bowel movements.
**Correct Answer:** C. Lactose