1 Background Multicellular organisms, such as plants and animals, have various levels of organization within them. Although individual cells can perform specific functions, they become dependent on one another and can work together for the good of the entire organism. The first level, cells, is the simplest level. Cells are the basic structural and functional units in living things. Examples of animal cells include blood cells, bone cells, nerve cells, and skin cells. Examples of plant cells include root cells, guard cells, and sieve tube cells. The next level, tissues, is made up of cells that are similar in structure and function. These cell groups work together to perform a specific activity. Humans, for example, have four basic tissues: connective, epithelial, muscle, and nerve. Plants have three basic tissues: dermal, vascular, and ground. Organs are made up of tissues that work together to perform a specific activity. Examples of this level for a human are the heart, brain, skin, and stomach. Organs found in plants include leaves, stems, and roots. Continue to the next page. Animal Plant cell cell tissue tissue organ organ 6.L 14.1 Organization of Organisms