1. Cell: The basic, fundamental unit of life. All living things are made of cells.
2. Tissue: A group of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, and epithelial tissue.
3. Organ: A structure made up of different tissues that work together to perform a complex function. Examples include the heart, lungs, stomach, and brain.
4. Organ System: A group of organs that work together to carry out major bodily functions. Examples include the digestive system, the circulatory system, and the nervous system.
5. Organism: A complete living being made up of multiple organ systems that work together to maintain life.
Therefore, the correct order from simplest to most complex is:
Cell → Tissue → Organ → Organ System → Organism
