In the middle grades students expand their knowledge of living systems to include the study of cells, the fundamental units of life.

In grade five students learned about the organs or tissues for respiration, digestion, waste disposal, and transport of materials in plants and animals. They were also first introduced to cellular functions when they studied cellular respiration in animals and plants and photosynthesis in plants. These studies are complemented in grade seven by new material on the cellular organelles responsible for those functions.

The standards in grade six covered ecology, and students in that grade learned how energy in the form of sunlight is transformed by producers into chemical energy through the process of photosynthesis. The study of energy transfer through food webs provided a foundation for a more detailed exploration at the cellular level of how plant chloroplasts capture sunlight energy for photosynthesis and how mitochondria liberate energy for the work that cells do.