GED Science Practice 2026 – 400 Free Practice Questions to Pass the Exam

Carbohydrates serve as an essential structural component of living cells and are a significant source of energy for animals. In the context of cellular structure, carbohydrates contribute to the formation of cell walls in plants, and they play crucial roles in cellular signaling and recognition processes. For animals, carbohydrates are primarily utilized as a quick source of energy; they are broken down during metabolic processes to provide glucose, which fuels cellular activities.

The other choices do not fulfill both criteria. Carbon dioxide is a waste product of respiration in animals and is used by plants in photosynthesis but does not serve as a structural component or an energy source for animal cells. Carbon monoxide is a toxic gas that can interfere with cellular respiration and does not provide any energy or structural benefits. Cartilage, while an essential part of animal anatomy and providing structural support in joints, is not a general source of energy or a fundamental component of all cells. Thus, carbohydrates are the clear choice for being both an important structural element and a primary energy source for animals.