There are several key concepts introduced in this chapter: Structure correlates with function; an animal's body has a hierarchy of organization with emergent properties at each level; and complex bodies have structural adaptations that increase surface area for exchange. Label the tissue layers shown in this section of the small intestine, and describe how this diagram illustrates these three concepts.

The principle of structure correlating with function suggests that the physical form of a biological structure is closely related to its role in the organism. For example, the small intestine's villi and microvilli increase surface area, enhancing nutrient absorption. This relationship is fundamental in biology, as it explains how adaptations arise to meet specific physiological needs.

Biological systems are organized in a hierarchical manner, from cells to tissues, organs, and systems. Each level of this hierarchy exhibits emergent properties, meaning that the whole exhibits characteristics that are not present in its individual parts. In the small intestine, for instance, the arrangement of epithelial cells into layers allows for complex functions like digestion and absorption, which are essential for survival.

Complex bodies often develop structural adaptations that maximize surface area for processes such as exchange and absorption. In the small intestine, the presence of folds, villi, and microvilli significantly increases the surface area available for nutrient absorption. This adaptation is crucial for efficient digestion, allowing the organism to extract maximum nutrients from food.