1. Cells: The basic unit of life, cells are the smallest structures that can carry out all the processes necessary for life.

2. Tissues: Groups of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, and epithelial tissue.

3. Organs: Structures made up of different tissues that work together to perform a more complex function. Examples include the heart, lungs, and stomach.

4. Organ Systems: Groups of organs that work together to carry out major bodily functions. Examples include the circulatory system, the digestive system, and the nervous system.

5. Organism: A complete living being made up of multiple organ systems that work together to sustain life.

These five levels of organization are hierarchical, meaning that each level builds upon the previous one. This organization is essential for the complexity and efficiency of living organisms.