Which one of the following sugars is not a monosaccharide and therefore does not belong to the simple sugar group listed?

Introduction / Context:
This question tests your understanding of basic carbohydrate classification. Monosaccharides are single sugar units, whereas disaccharides consist of two monosaccharide units joined together. Recognising which listed sugar is not a monosaccharide is important in biochemistry and nutrition based general knowledge.

Given Data / Assumptions:
- The options include galactose, glucose, fructose, and maltose. - The question asks which is not a monosaccharide sugar. - Standard biochemical definitions of mono and disaccharides are assumed.

Concept / Approach:
Glucose, fructose, and galactose are all hexose monosaccharides, meaning they contain six carbon atoms in a single sugar unit. Maltose, on the other hand, is a disaccharide composed of two glucose molecules linked by a glycosidic bond. Therefore, maltose is not a monosaccharide but a disaccharide, making it the correct answer to this question.

Step-by-Step Solution:
Step 1: Recall that glucose is a common blood sugar and a classic example of a monosaccharide. Step 2: Remember that fructose is a monosaccharide found in fruits and honey and is also a hexose sugar. Step 3: Recognise that galactose is another monosaccharide that combines with glucose to form lactose in milk. Step 4: Note that maltose is formed when two glucose molecules join during starch digestion, so it contains two sugar units. Step 5: Understand that a sugar with two linked units is classified as a disaccharide, not a monosaccharide. Step 6: Conclude that maltose is the sugar that is not a monosaccharide.

Verification / Alternative check:
As a quick verification, think of common disaccharides: sucrose, lactose, and maltose. All of these are known to be composed of two monosaccharide units. By contrast, glucose, fructose, and galactose cannot be split into simpler sugars by hydrolysis. Textbooks and exam tables clearly list maltose as a disaccharide formed from two glucose units. This confirms that maltose is not a monosaccharide and matches the question requirement.

Why Other Options Are Wrong:
Galactose: This is a monosaccharide that, along with glucose, forms lactose in milk and is not a disaccharide. Glucose: This is the primary monosaccharide circulating in blood and serving as a fuel source for cells. Fructose: This simple sugar is a monosaccharide present in fruits and honey and is not formed by joining two sugar units.

Common Pitfalls:
Students sometimes confuse sugar taste or sources with structural classification. For example, they may know that fructose is very sweet and mistakenly think it is complex. Another pitfall is to forget that names ending in ose can refer to both mono and disaccharides. To avoid confusion, memorise that glucose, fructose, and galactose are monosaccharides, whereas sucrose, lactose, and maltose are disaccharides.

Final Answer:
The sugar that is not a monosaccharide is Maltose.