NSES Content Standard C 
Life Science: Structure and function in living systems
Grades 5-8, page 156

Living systems at all levels of organization demonstrate the complementary nature of structure and function. Important levels of organization for structure and function include cells, organs, tissues, organ systems, whole organisms, and ecosystems.

Benchmark 5A The Living Environment: Diversity of Life
Grades 6-8, page 104
Animals and plants have a great variety of body plans and internal structures that contribute to their being able to make or find food and reproduce.