**Core Concept**
Glucose is a fundamental monosaccharide, a single sugar molecule that serves as a building block for more complex carbohydrates. Monosaccharides are the simplest form of sugars, consisting of a single sugar unit. They are essential energy sources for cells and play a crucial role in various physiological processes.

**Why the Correct Answer is Right**
Glucose is a monosaccharide because it does not undergo hydrolysis into simpler sugars. Instead, it can be broken down into pyruvate through cellular respiration, releasing energy for the cell. Glucose is a vital energy source for cells, particularly neurons and red blood cells, which rely heavily on glucose for their energy requirements.

**Why Each Wrong Option is Incorrect**
**Option A:** Fructose is a monosaccharide, but it is not the correct answer in this context. Fructose is a type of sugar that is often found in fruits and is primarily metabolized in the liver.
**Option B:** Sucrose is a disaccharide, composed of glucose and fructose molecules bonded together. It is not a monosaccharide.
**Option C:** Maltose is another disaccharide, composed of two glucose molecules bonded together. Like sucrose, it is not a monosaccharide.

**Clinical Pearl / High-Yield Fact**
Glucose is the primary energy source for the brain, accounting for approximately 60% of its energy requirements. This highlights the importance of maintaining normal glucose levels to ensure proper brain function.

**Correct Answer:** C. Glucose