A Level Biology Practice Exam

What are carbohydrates primarily composed of?

1. Carbon, hydrogen, and nitrogen

2. Carbon, hydrogen, and oxygen

3. Oxygen, nitrogen, and sulfur

4. Hydrogen, carbon, and phosphorus

The correct answer is: Carbon, hydrogen, and oxygen

Carbohydrates are primarily composed of carbon, hydrogen, and oxygen. The general formula for carbohydrates can often be represented as \( C_n(H_2O)_n \), highlighting the presence of these three elements in a fixed ratio. The carbon forms the backbone of the carbohydrate structure, while the hydrogen and oxygen typically appear in proportions that reflect water molecules. In terms of structure, carbohydrates can exist as simple sugars (monosaccharides like glucose) or more complex forms (disaccharides like sucrose, and polysaccharides like starch and cellulose). Regardless of their complexity, the fundamental composition remains consistent with the inclusion of these three elements. Understanding this composition is crucial in biochemistry, as carbs play vital roles in energy storage, providing structural integrity in cell walls, and serving as important signaling molecules.