PLTW Human Body Systems Practice Test 2026 - Free Human Body Systems Practice Questions and Study Guide

The small intestine plays a crucial role in the digestive system, as it is the primary site for the absorption of digested nutrients. After food is broken down chemically in the stomach, it enters the small intestine where enzymes and bile further aid in digestion. The inner lining of the small intestine is lined with villi and microvilli, which significantly increase the surface area for absorption. This structural adaptation allows for efficient uptake of essential nutrients, such as carbohydrates, proteins, and fats, directly into the bloodstream.

While vitamins and minerals are indeed absorbed in the small intestine as well, the primary focus of this question pertains to the overall absorption of all digested nutrients. Additionally, water and electrolytes are primarily absorbed in the large intestine, while oxygen and carbon dioxide are gases exchanged in the lungs, not absorbed in the digestive tract. Thus, choosing digested nutrients reflects the primary function of the small intestine in the digestive process.