Groups of specialized cells cooperate to form a tissue, such as a muscle. Different tissues are in turn grouped together to form larger functional units, called organs. Each type of cell, tissue, and organ has a distinct structure and set of functions that serve the organism as a whole. The human organism has systems for digestion, respiration, reproduction, circulation, excretion, movement, control and coordination, and for protection from disease. Disease represents a breakdown in structures or functions of an organism.
Some diseases are the result of intrinsic failures of the system.
Others are the result of infection by other organisms. The cell is the basic unit of living things. Content Standard Life Science 6-8 NSES Content Topic Populations And Ecosystems Populations consist of all individuals of a species that occur together at a given place. All of the populations living together and the physical factors with which they interact compose an ecosystem. Populations of organisms can be categorized by the function they serve in an ecosystem.