The document discusses the organization of cells in multicellular life forms. It explains that cells are organized into tissues that work together to perform specific functions, such as muscle tissue for movement. Tissues then combine to form organs like the skin or lungs. Groups of organs that work together on different body functions are called systems, such as the respiratory, circulatory and excretory systems which are involved in nutrient exchange. The document provides examples of the nutrition, interaction and reproduction functions carried out by systems within the human body.