IB Biology Practice Exam

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically in a ratio that fits the general formula \( C_n(H_2O)_n \). They are primarily recognized as a key source of energy for living organisms, as they can be easily broken down through metabolic processes to release glucose. This glucose can then be utilized by cells for immediate energy or converted to other forms such as glycogen for storage.

In addition to their role as an energy source, carbohydrates also serve structural purposes. For example, cellulose, a type of carbohydrate, forms the structural component of the cell wall in plants, making it vital for maintaining cell shape and integrity. Chitin, another carbohydrate, provides structural support in the exoskeletons of arthropods and cell walls of fungi.

While proteins and lipids can also serve as energy sources, their primary roles involve building and maintaining cellular structures (for proteins) and long-term energy storage and signaling (for lipids). Nucleic acids, on the other hand, are primarily involved in storing and transmitting genetic information rather than serving as a source of energy or structural materials. Thus, carbohydrates hold a central position in both energy provision and structural support in biology.