Different tissues are in turn grouped together to form functional units, called organs. Each type of cell, tissue, and organ has a distinct structure and set functions that serve the organism as a whole. The human organism has systems for digestion, respiration, circulation, excretion, movement, control, coordination, and for protection from disease. These systems interact with each other. Disease is a breakdown in structures or functions of an organisms.
Some diseases are the result of intrinsic failures of the system.
Others are the result of damage by infection by other organisms. Safety and security are basic needs of humans. Safety involves freedom from danger, risk, or injury. Security involves feelings of confidence and lack of anxiety and fear. Student understandings include following safety rules for home and school, preventing abuse and neglect, avoiding injury, knowing whom to ask for help, and when and how to say no.