This document discusses the organizational levels of life, from cells to systems. It states that the cell is the basic structural and functional unit of life, and that plant cells and animal cells have different structures when viewed under a microscope. It also explains that tissues are groups of cells organized to perform specific functions, organs are made of different tissues working together for a function, and systems are groups of organs that work together for a specialized function. Overall, it provides an overview of the hierarchical organization of living things from cells to systems.