List of levels of organization from simple to most complex.

LEVEL 1 - Cells

* Smallest working unit of structure and function in living things. * May serve a specific function within the organism * Examples- blood cells, nerve cells, bone cells.

LEVEL 5 - Organisms

*Entire living things that can carries out all basic life functions. Meaning they can take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce. *Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protist. *Examples - bacteria, amoeba, mushroom, sunflower, human, and animal.

LEVEL 2 - Tissues

*Made up of cells that are similar in structure and function and which work together to perform a specific job. *Examples - blood, nervous, bone, etc. Humans have 4 basic tissues: connective, epithelial, muscle, and nerve.

LEVEL 3 - Organs

*Made up of similar tissues that work together to perform a specific activity. *Examples - heart, brain, skin, etc.

LEVEL 4 - Organ Systems

Groups of one or more organs that work together to perform function for the organism. Examples - circulatory system, nervous system, skeletal system, etc. The Human body has 11 organ systems - circulatory, digestive, endocrine, excretory (urinary), immune(lymphatic), integumentary, muscular, nervous, reproductive, respiratory, and skeletal.