Structure of matter - Is it complex?

Turning briefly to the field of zoology, we note that multicellular animals exhibit a hierarchical structure similar to that of plants: Collections of cells form tissues, tissues work together as organs, clusters of organs define systems (such as the digestive system), and so on. We cannot help but again notice God’s awesome economy of expression: The fundamental building block of all animal matter is the cell, just as the cell is the elementary structure of all plant life.

Granted, there are differences between these two. For example, plant cells are enclosed by rigid cellulose walls, but animal cells are not. Notwithstanding these differences, however, both of these structures are undeniably cells. This is an example of commonality that crosses domains. A number of mechanisms above the cellular level are also shared by plant and animal life. For example, both use some sort of vascular system to transport nutrients within the organism, and both exhibit differentiation by sex among members of the same species.