1. Cells: The basic, fundamental unit of life. They carry out all the essential life processes.
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 perform a major bodily function. Examples include the digestive system, circulatory system, and nervous system.
It's important to remember that these levels are hierarchical, meaning that each level builds upon the previous one. Cells form tissues, tissues form organs, and organs form organ systems. This hierarchical organization allows multicellular organisms to carry out complex functions and maintain homeostasis.
