Levels of Organization
Some living things contain one cell that performs all needed functions. Multicellular organisms are made of many parts that are needed for survival. These parts are divided into levels of organization. There are five levels: cells, tissue, organs, organ systems, and organisms.
All living things are made up of cells. This is what distinguishes living things from other objects. Cells are the basic building blocks of all organisms. Although cells are made of smaller parts, none of those parts could survive on their own. Cells are the simplest level of organization.
Many cells working together form tissue. The cells involved are specialized to cooperate with each other to accomplish one common goal. There are many different types of tissue in both plants and animals.
When there are layers of tissue working together, they form an organ. All animals contain organs. In fact, mammals have five vital organs that they cannot live without: kidneys, lungs, liver, heart, and brain.
When organs work together, they form organ systems. Organ systems keep the body regulated and in a stable state. These systems often work together and rarely work in isolation. The human body has 11 organ systems.
Organisms are technically any form that can carry out its own functions such as take material in and push material out. Some fully functioning organisms are made of just one cell. For the purposes of the level of organization, organisms are made up of many organ systems working together.