Which of the following is NOT a form of monosaccharide sugar?

Introduction / Context:
Carbohydrates are important biomolecules that can be classified into monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simplest sugars and serve as basic building blocks for more complex carbohydrates. Understanding which sugars are monosaccharides and which are not is fundamental in biochemistry and nutrition. This question asks you to identify the sugar that is not a monosaccharide among the options given.

Given Data / Assumptions:
• The options are galactose, glucose, fructose, and maltose. • The task is to find the sugar that is not a monosaccharide. • Standard classification of carbohydrates is assumed.

Concept / Approach:
Glucose, fructose, and galactose are all monosaccharides, often called simple sugars. They have the general formula C6H12O6 and differ in the arrangement of atoms. Maltose, however, is a disaccharide composed of two glucose units linked together. Disaccharides are formed by condensation of two monosaccharide molecules and can be broken down by hydrolysis. Therefore, maltose is not a monosaccharide, while the other three sugars are monosaccharides.

Step-by-Step Solution:
Step 1: Recall that glucose is a well known monosaccharide and an important energy source in the body. Step 2: Remember that fructose is a monosaccharide commonly found in fruits and honey. Step 3: Recognize that galactose is also a monosaccharide, often found as part of lactose in milk. Step 4: Know that maltose is a disaccharide formed by the combination of two glucose molecules. Step 5: Choose maltose as the sugar that is not a monosaccharide.

Verification / Alternative check:
Biochemistry tables list glucose, fructose, and galactose under monosaccharides, while lactose, sucrose, and maltose are listed under disaccharides. In digestion, enzymes such as maltase break down maltose into two glucose units, clearly demonstrating that maltose is not a single simple sugar. These references support the classification of maltose as a disaccharide and confirm that it is not a monosaccharide.

Why Other Options Are Wrong:
Option A (Galactose) is incorrect because galactose is a monosaccharide with the same molecular formula as glucose and fructose. Option B (Glucose) is incorrect because glucose is the primary monosaccharide used for energy in cells. Option C (Fructose) is incorrect because fructose is a monosaccharide found naturally in many fruits.

Common Pitfalls:
Students sometimes confuse the names of various sugars and may not remember which ones are mono or disaccharides. A helpful method is to recognize that names ending in ose are sugars, but their classification depends on their structure. Remember that maltose, sucrose, and lactose are classic disaccharides, while glucose, fructose, and galactose are classic monosaccharides.

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