Lactose is made up of :

The correct answer is D, Glucose and Galactose. Lactose, the sugar of milk, is a disaccharide formed when one molecule of glucose joins one molecule of galactose. Disaccharides are sugars made of two simple sugar units, or monosaccharides, linked by a glycosidic bond. In the small intestine the enzyme lactase splits lactose back into glucose and galactose, which are then absorbed into the blood. Many adults make less lactase as they grow older, so undigested lactose reaches the large intestine, where bacteria ferment it and cause bloating and discomfort; this is called lactose intolerance. Curd and cheese contain less lactose because bacteria have already used much of it. Option A is wrong because glucose alone makes maltose (two glucose units) or polysaccharides such as starch, not lactose. Option B is wrong because glucose and fructose together form sucrose, the common table sugar from cane and beet. Option C is wrong because sucrose is itself a disaccharide, and lactose contains no sucrose. Exam tip: sucrose is glucose plus fructose, lactose is glucose plus galactose, maltose is glucose plus glucose.